Corally Rear Wheel Bolts M2.5 !!!!

When I first built my "US Spec" Corally SP12X, I was expecting to fit standard 1/12th wheels with standard imperial bolts. This was not to be the case.

Corally are pasionate about doing this all in metric like the true Europeans they are.... as a result you are going to have to find metric M2.5 hex bolts to secure your wheels to diff and offside hubs.... these are as rare as rocking horse poo and they were ommitted from my kit! Argh!

Tip Number 1. The bolts used on standard brushed motor end bells are M2.6 and these will do the job in an emergency (thanks Pete).

Tip Number 2. I get my M2.5 screws from here http://stores.ebay.co.uk/stainlessbolts

They do 8mm ones but it is REALLY important that you file them down to 7mm long (threaded part) and no longer. If the screws are too long they do through the hub on the diff side and collide with the diff ring which will really mess up your diff action!

Corally SP12X Diff Nut Trick

I have noticed a few people suffering from the diff nut coming loose on the SP12X. Unlike other diffs, the Corally uses a carbon nut on a carbon threaded shaft. There is no lock nut as such and the location of the diff nut is reliant on the nut/thread friction and the grip offered by the serrated locking washer.


The Corally diff is one of the best I have used with a great smooth and reliable action provided by the outer thrust race that comes as standard. I have a tip here that will solve or prevent the diff nut coming loose. Before we start be warned!!!!

Warning 1. The tiny thrust race balls are NOT captive within the spacer and its "game over" if these go on the carpet!

Warning 2. I am going to do stuff with superglue, fingers, carbon parts and tissue paper. We need to make sure that all 4 of these components are separate at the end of the process.

Step 1. Read Warning (1) above and strip your diff down. We want the shaft.

Step 2. Place a small drop of super glue on the threaded part of the shaft and then quickly and evenly wipe it into the thread with tissue paper, forming a smooth and thin (very thin) layer coating of super glue over the thread. Do not allow super glue to touch the non threaded parts of the shaft.






We are not looking to fill up the thread groves with glue here. The objective is to use the glue coating to slightly oversize the thread.

I used a standard viscous super glue off the DIY shop shelf. I would worry about the "Orion" type of watery thin cyano that is popular for mounting rubber tyres. Introduce a drop of this and it can capillary itself all over the the thread, the shaft, your car, your fingers and the work table! That's Warning (3).

Step 3. Wait Wait WAIT for the glue coating to fully dry before you try the nut on the thread. You really do not want to superglue the nut to the shaft here! Try the nut on the shaft, it will now feel tighter. Ideally you want it to fell tight enough to be difficult to turn using your fingers alone but easy with your diff spanner. I repeated step 2 a couple of times until my nut was "locky" enough.

Step 4. You may now find the spur gear bearing will not pass over the thread as you have slightly increased the outer diameter with the super glue coating. This is easy to rectify. Just rotate the shaft by hand while holding the thread with some fine abrasive paper wrapped around it. This will remove some of the super glue and reduce the outer diameter of the shaft whilst keeping the coating in the thread groves.

Job done!

A final tip. I alway loosen the diff off after the end of a meeting. This prevents the O ring being over squashed and distorted.

Cheers


Mark

SP12X T-Bar Setup

Credit for this info to Peter Winton and Roger Manwaring

OK.... the T bar that comes in the Corally SP12X kit as standard is a 2mm piece. This is the one I think most people run in the UK on our "medium bite" carpet conditions but with two minor deviations.

Firstly the more recent Corally 2mm Tbars were strengthened which made them slightly stiffer. I am advising that you modify the T bar by filing away some of the material as shown in black on the following pictures. You can see below with one side only done to reveal the difference.

I use a set of small "diamond" grit files to do this (get them from most craft shops) as carbon and glass fibre ruins carbon steel tools. Keep the curve libe in the T bar as shown so as to not introduce a stress point.

Secondly, when you install the T bar, do not use the glass fibre spacer that comes in the kit. Use two washers of 1.6mm thickness or chop the little round ends off the spacer supplied in the kit to make the "washers". The idea is to keep a little more flex in the rear part of the T-Bar.

Also DO NOT install the centre screw. This stops the flex we want and I have seen the centre screw wreck the motor pod carbon under tray when and if the T-Bar breaks in a crash. Leave it out!

Photo on the left above shows the centre screw out.

Photo on the right. Two spare parts that all SP12X drivers should carry! Mine are as yet unused ;-)

Corally SP12X : Front End

Corally SP12X and the Associated Front End

In the UK we pretty much all use the Associated (AE) front end on the Corally SP12X. To be honest, I have never run the Corally one that comes in the box, pretty as it is! If the AE is what the World Champion uses then thats good enough for me!

I had enough Associated bits left over to build a front end up but you can now purchase the complete front end conversion kit from Corally as a "blueprinted" set. The part number for this is 75950 and its called the "12X WC Front suspension conversion kit". More details are here:

http://international.corally.com/news/news.htm

The chassis is predrilled to take the AE front arms so you will have no problems here.

You do have to drill two new servo mount holes in the chassis 8mm back from the rearmost set that are drilled as standard. To do this you will want a sharp 3mm drill and countersink bit. Remember carbon fibre really kills cutting tools!

The exact lateral (sideways!) location of the holes depends on the servo you use. Try to leave the servo mount posts a little wide (by say 2mm) so you can adjust the servo position to get it exactly in the centre. Think and double check yourself. It is important the the servo drive spline ends up crack on the centre line of the car.

If you need good instructions on how to build an AE front end accurately, you will find then in this blog... read on.

Mark joins Corally Team. SP12X

Changing To Corally

I had to try something different! Since winning the 2005/2006 F2 19T and Modified Championships in the UK, my first year (2006/2007) as an F1 driver was not great to be honest. I like to improve and feel I am making progress but had hit a brick wall. I had a bad Worlds followed by a bad Euros and started to loose confidence.

Going Backwards

I seemed to be going backwards with the CRC. I had the 3.2R with the ABP chassis running really well but the move to GenX was not working for me. In fact I had my best results last year with a CRC T-Fource. There are many many top drivers doing well with the GenX but I think we have a particular problem in the UK with lower traction (compared to the US) which suit’s a T Bar car over a link car.

The Final Straw

The final straw was at the first of the Chesterfield summer events where I left the meeting in an internal frustrated temper before the finals. I have never left an RC race even when having a bad day…..

Watching the Competition

Remember that I am only an ok_to_good driver and I think a lot of the problems ended up in my head. Either way … it was time for a change. I had been watching Roger Manwaring in the UK put the Corally SP12X down and instantly appear to be smooth and precise. I must admit that I am a little influenced by David Spashett also! With other upper mid-field F1 drivers including Rambo (Michael Ramsbottom) and Mark Jewitt doing well (and getting away from me) and rising stars like Chris Kerswell and Matt White making A finals, I decided on the Corally (what a terrible sheep I am!)

So here it is…. I will be updating the 12th blog with more Corally specifics as I learn them.
Many thanks to Pete Winton, Roger Manwaring and David Spashett who have got me hitting the ground running. Two meetings later and I have this huge smile on my face once again.

For people new to 1/12th in the UK (I am meeting quite a few on my travels!), I would point you to Action Model Centre. They support our national series and have all 1/12th stuff in stock. They also do a good price on the SP12X!

http://www.actionmodelcentre.com/

Cheers
Mark

CRC GenX Pro Strut Front End. Review and Building Tips

Detailed Review and Building Tips for the CRC Prostrut Front End

CRC Prostrut Front End

This has to the most radical development introduced on the GenX car. CRC have moved away from taking the Associated OEM front end from the L4 and created a front suspension system with a similar geometry albeit with a many new and unique features.



New Prostrut on the left with the Associated (with CRC Parts!) on the right.

The Prostrut system is totally compatible with the mounting holes of the Associated suspension allowing many (most!) drivers to take advantage of this new development.

New Features



1. The kingpins are threaded at the steering block end, allowing the adjustment of kingpin spring preload without the use of shims.

2. The steering arm pivots the king pin in a ball joint pressed into the lower A arm. This is similar to the Associated design but the top of the steering block terminates in a new pillow ball coupling (rather like a small version of the original Xray T1 touring car).



3. Both the top and bottom steering arm joints can be adjusted for wear and "slop".



4. Four castor angle options are available (3 on the Associated) by configuring the three Teflon spacers. These spacers can be moved easily without having to rethread the inner pivot pin. The castor block has a split design that allows this feature.

5. Reactive castor blocks (0, 5 and 10 degree, ala Associated) can be changed without removing the front suspension from the chassis.

6. The front axle diameter is increased to 3/16th inch, this requires different front wheel bearings but is almost impossible to bend.

Associated to CRC Pro Strut Geometry Comparison



Track Width

The picture shows a Pro Strut lower arm bolted to an Associated arm. The objective here is to show that the lower pivot ball location is almost identical. In fact the CRC pivot ball is 0.5mm closer inboard. This can be seen by the slight angle that a pin running through both pivots balls creates.



You may think that this would result in the front track width being 1mm shorter overall with the Prostrut but this is not the case. The CRC steering block places the inner wheel bearing surface 0.4mm further outboard (on each side). The photo below shows the Associated on the left and new CRC block on the right. The result is that although the kingpins are approx 1mm closer together on the Prostrut, the overall front wheel track width will be the same as the Associated setup.



Reactive Castor

The 0 degree, 5 degree and 10 degree reactive castor blocks on the Prostrut mimic the Associated geometry and place the inner top pivot pin at the same relative heights front and back. However, and this is a big difference, the inner upper link pin is much further outboard on the Pro Strut, lying directly over the chassis mounting hole centres. This makes the CRC upper suspension arm shorter by about 5mm on the (37mm for the Associated and 35mm for the Prostrut).



Short Arm

The shorter CRC top arm connects inner and outer pivot points at the same relative heights when compared to the Associated. This means that the top arm is more angled on the CRC (as well as being shorter).

The shorter CRC top arm should result in more camber change as the suspension compresses, as does the increased arm angle. The increased arm angle also lifts the front roll centre higher.

To be honest, I am unsure of the overall effect here. Camber change can be argued to increase grip (at the front) where the raising of the front RC decreases it! I have shown you the difference. Test it and see how it feels!

Castor Options

The GenX manual suggests to start with all Teflon washers forward (minimum castor). I have looked at this with the 0, 5 and 10 degree reactive blocks and the resultant castor angles are as follows (measurements taken with no compression):

All three shims forward ... -3 degrees (the king pin is going FORWARD!!!)
Two forward, one back ... 0 degree castor
One forward, two back ... 3-degree castor
All three shims back... 6-degree castor.

I would normally run the 3 or 6-degree options. To be honest I see no sense in the forward leaning king pin. You have been warned!

The three Associated options (no compression) would be 2,4 or 6 degrees depending on the shim positions.

Springs

The CRC springs are shorter than the Associated ones by around 0.5mm (0.020"). You could run the Associated springs but you will run into problems here if you are not running CRC hi-roller wheels as the extra 0.5mm length adjusted into the king pin fouls the inside of a "standard" front wheel.

The larger CRC hi-roller wheel allows you to run whatever spring you like, CRC or Associated. Personally I run the CRC springs and have settled on the CRC 0.50mm spring which is slightly harder than and Associated 0.020". Note the CRC springs end up being a little harder for the same metal diameter as CRC spring coil density is less (less turns per mm of spring length).

Building The Pro Strut

These tips are in addition to the Gen X Manual.

1. Ident Your Castor Blocks



The reactive blocks are not marked as to 0 degree, 5 degree or 10 degree. As shown, I paint a little white Tipex blob and write on the block angle with a thin marker pen. Hopefully this will help prevent ending up with different blocks on each side (been there, done that).

2. Hand Finishing the Upper "A" Arm



The secret of reliable handling lies in free movement of the front end. It must not stick or bind. I use a 2mm drill (by hand) to ream out the upper arm pivot holes. Work the drill by hand until the pin rotates freely.

3. Finishing the Castor Blocks



I find the split castor block slightly oversized, again causing the upper suspension arm to bind. Assemble the top part of the molding and screw it down. Grind the length down slightly rubbing on abrasive paper. Do this until the upper arm does not bind.

4. Upper "A" Arm Binding Check



When you assemble the upper arm it should drop under its own weight. This is a good test to make sure there is minimal friction here. If it "stays where you put it" its time to revisit step 2 or 3.

5. Teflon Balls

CRC provide a delrin lower pivot ball in the kit. It's fine but I prefer to use the Teflon coated metal ball ( http://rc4less.safeshopper.com/22/389.htm?692 ) that I also used in the Associated front end. Now here lies a problem:



A standard Associated 1/8th inch (0.1250" in theory) king pin measures 0.1240" diameter giving 1 thou of running clearance, the CRC threaded king pin is very accurately ground to exactly 0.1245" resulting in only 0.5 thou of clearance.

The result is that the CRC king pin is perfect in the CRC delrin ball but it binds in the part I want to use! My solution is to polish down the CRC king pin diameter by popping it into my dremel and rotating it in 240grade abrasive paper (lubricate with spit!) followed by 1500 grade finishing with wire wool to put the polish back.

6. Upper Pillow Ball



When assembling the pillow ball upper joint, do not over tighten it. There is no point in doing this. There is nothing wrong with a little suspension slop. Its really nice with the CRC Prostrut to have the adjustment to take out wear but if you overdo it, your suspension will bind up on the track.The GenX manual suggests tightening it up and then working the ball joint by hand to break in the parts. Do this but then remember to slacken the screw out slightly to free up the ball joint. Check this after your first few meetings and readjust once things have worn in.

7. Lower Clamping Screw

The same is true for the clamping screw that takes out the play in the lower A arm ball joint. Do not over tighten this. The manual suggests that there should be "just a little drag" resisting the movement of the lower ball. Sorry but I disagree here, I would suggest you set this for "just a little play". If the lower ball is not free to move it puts a binding load on the movement of the kingpin. Again check after a few meetings and readjust allowing for break-in.

8. Binding Check

Assemble the whole front end as per the manual but don't lock the king pin in place (leave the small set screw loose for now) and don't put the spring or e-clip in place. This will be your final check for binding. The king pin should move freely up and down through the lower ball joint. If you push the king pin through the ball (as if compressing the spring that is absent (!)), the whole steering block/upper arm assembly should drop back into place under its own natural weight, without binding or restriction.

9. Adjusting the Kingpins

Once the suspension is free, its time to put on the springs and e-clips. Using a 0.050" driver screw the kingpin in until the spring just touches the e-clip and the play is taken out of the suspension. Remember this is with no load on the spring as the Prostrut suspension is still in your hands and not on the car!



Compress the spring a few times to "pre shrink" any shortening that often occurs when the springs bed in. Readjust to take out the play.Now it comes to tighten the grub screws that will hold the kingpin in place and prevent it from rotating. A word of warning here:

The original grub screws were steel, threaded into the alloy axle piece and made tight onto the screw thread of the king pin. The risk here is that if you over tighten the grub screws, you damage the threads in the axle block on the kingpin itself.I think CRC changed the grub screw for brass in the second run of kits and these are available as a part here:

http://www.teamcrc.com/crc/modules.php?name=Shopping_Cart&file=product&c_op=viewprod&prodID=7718936

10. Threading the Lower "A" Arms

I have seen reports of people smashing lower A arms in crashes not deemed worthy of breakage. I run unlimited modified class and I have launched the car into various obstacles without problems.

Bottom line is that I have a pit box full of broken Associated A arms and I am sure there will be some CRC stock to add soon! Keep spares. If this part does not break in a bad crash it will rip itself out of your carbon chassis, I know what I prefer.

However, what does worry me is reports of people splitting the arms around the mounting screw holes as they cut the threads in for the first time. The GenX kit supplies a stainless steel screw to do this and you should use it, but here is a tip:



We are going to use a cutting wheel on a dremil to convert the GenX kit screw into a tapping bit. Simply cut two slots in the thread as shown on opposite sides (180 degrees apart). You could also do this with a needle file and some patience.

Now when you use this tool it will cut a thread rather than "force" a thread. This will reduce the risk of damaging the part while cutting the thread the first time and it will go onto the car without the holes being held in expansion stress.

11. Grinding the carbon ride height spacer

I have stopped using the pretty red ride height collars. Your mileage may vary but I have managed to crush/deform two of them in a bad accident leading to errors in ride height accuracy (readers of my stuff will know I am very anal about these details!).

I would prefer to see a little more alloy in theses but in the meantime: CRC make a must have alternative lowered carbon spacer:

http://www.teamcrc.com/crc/modules.php?name=Shopping_Cart&file=product&c_op=viewprod&prodID=7718937



These spacers will allow you to run smaller front tyres and also are recognised as adding strength to the front end. The picture shows the grinding I do on these before using. Do not use them without such a modification, as they will tweak the front end by putting pressure on the heads of the screws that secure the castor blocks.

12. Attaching the Prostrut

The final step is to attach the front end to the chassis. As with the Associated front end it is important to not over tighten the 8-32 screw otherwise you will deform the alignment of the lower A arms leading to left/right ride height differences. You also risk deforming the chassis carbon around the countersunk holes making accurate seating of the arms more difficult.The screws need to be just tight to hold the suspension without movement and no more. I like the Lunsford titanium screws available here:

http://www.lunsfordracing.com/mm5/merchant.mvc?Screen=PROD&Store_Code=LUNS&Product_Code=A8F0500&Category_Code=STDFLAT

Spektrum DSM Review: KO Vantage Upgrade

Spektrum DSM Radio System Review



Preamble… Before we start… I will tell you that I have converted my KO Esprit Vantage II (Type R) to Spektrum DSM. This is a one-way street, you cannot convert back again, so I had to be sure. Two meetings later and I am very happy…. Here is the longer version.



Well I waited and waited:

On the surface it was an irresistible proposition: No more radio interference, no chance of a frequency clash. No need to carry multiple crystals, no queuing during practice sessions, waiting for a peg. No one from the next heat can turn on and wreck the end of your run…..

But you see, I am a cynic. There had to be a catch:

Well, I saw one catch… cars turning themselves off after collisions. Spektrum themselves document the issues here

http://www.spektrumrc.com/Articles/HobbyWire.aspx

I saw it for myself in the UK with the 2005 “early adopters” and even at the 2006 12th scale Euros back in March 2006 with some cars taking a hit and needing to be turned off and on again to get going again… why would I want that?

But they fixed it. A hardware antenna problem on the transmitter module was identified and a software update followed. Then came the Pro Series with reduced latency and I judged it was time for even old gits (like me!) and late adaptors to take the floor……

I like my Sticks

Since my return to RC racing in 1999 as a more “mature racer”, I bought a KO Vantage (later upgraded to a Vantage II Type R). I need sticks! I like this thing and
I had no desire to loose a friend in the pursuit of advancement.

My path into the world of 2.4Ghz RC was therefore to convert my KO Vantage to Spectrum DSM Pro Series

The One Way Street

The KO Vantage transmitter can be converted to accept the standard DSM transmitter module. This is a conversion (in the UK) that has to be carried out by Helger Racing http://www.helgerracing.com/

The conversion involves the permanent removal of the KO crystal module and it’s internal connectors within the transmitter. You get the module PCB back but the case becomes a blanking plate. The innards are coming home in a plastic bag!



A small backplane connector is installed in the TX and a neat hole is cut into the back of the rear case to take the Spektrum DSM Module.

The transmitter antenna is removed and the resulting hole finished off with a neat blanking plug.



… and that’s it.

Sell all of your old KO receivers because they are now unusable with your converted tranny.

Products

I purchased the SPM1013 Pro package for KO radios consisting of the SM1001 TX Module and Pro Receiver SR3001. The cost of this package in the UK is £165. In addition to this, the cost of the conversion to the Vantage is £47.50.

I also purchased the micro receiver (SR3500), which retails at £65. This goes into my 1/12th car (oh my gosh its small!) and the SR3001 has become the spare or for a second car.

Size Matters



As my comparison photo shows, the Standard SR3001 RX is just a little larger than the KO-301F RX and the micro SR3500 unit is even smaller than the tiny KO-302F. Any of these RX units will fit into a 1/12th car but the SR3500 is something special!



Voltage

The Spectrum system will work right down to 3.2V so even 4 cell 1/12th racing should be no problem.

I prefer to use a 5 cell RX pack in my 1/12th for three reasons:

(1.) I like the extra servo speed

(2.)We have found the brushless system can divert power from the motor at the end of a run with the 4 cell configuration making the car feel soft when in fact there is power to spare.

(3.) We have seen personal transponder counting errors if the loop is placed in a position where 4 cell cars “power up” due to voltage dip.

My choice of running the RX pack hence has nothing to do with the Spektrum system.

In Use



I have used the system at three events now without fault.

In the light of personal transponders, the old hand out units seem obviously outdated, who would want to go back? I think the Spektrum DSM system will do the same thing for crystal radio systems.

Advantages

I don’t have to think about turning on, no one can clash with me and I cannot interfere with anyone else.

It’s fast. I cannot tell the difference. The issue of speed seems irrelevant to me.

Relax between the qualifiers and the finals… there will be no crystals to change!

Apparently it will not glitch and I have no evidence to the contrary.

The SR3500 receiver is very very small. As is its antenna wire.

Disadvantages

I don’t like the balance change to the Vantage transmitter with the antenna missing. I will be fixing it back and running the system with a “dummy” aerial up.

I think it’s a bit expensive! But I’m worth it ;-)

www.spektrumrc.com will tell you all you need to know about the system
www.helgerracing.com for the UK distributer of KO Propo and Spektrum

Preparing 12th Scale Differentials

Building Tips for 1/12th Differentials

In a 1/12th scale diff, we require the balls to rotate between the thrust rings when cornering and not slip under driving torque. If you hold both wheels it should be very hard to force the spur gear around with your thumb yet the diff should feel smooth and free when the spur is held and one wheel is turned by hand (with the other moving in the opposite direction).

I use the large D ring diff that is standard on the CRC CK3.2 and CRC TFource. I am pretty sure this diff is the same basic design used on most of our cars (hmm not sure about Corally!). I tend to use the Kimbrough spurs, they use 12 balls around the outside of the spur.

Basically we want to tighten the diff lock nut just enough to keep the diff action whilst preventing the balls from slipping and compromising acceleration when the power goes down. If you over tighten, you compromise the handling of the car and wear out the differential prematurely.

I have found a few general things that increase the “grip” of the diff (resistance to slipping) while allowing the use of less thrust tension, resulting in better performance, less wear and longer life.

These notes are in two parts: In this part I present general tips for diff building. The second article will look at the add-on outer trust race from Slapmaster Tools.

General Building Tips:

1. It’s All About the Balls

Always degrease the diff balls and thrust rings with motor cleaner. Any residual oil (new parts often carry an oil film to protect against corrosion) will reduce the effectiveness of the silicone diff grease and reduce the “grip” of the diff.

I use ceramic diff balls from http://www.rc4less.com/ (see http://rc4less.safeshopper.com/22/446.htm?32 ) These last for ever and once installed and “run in” (see later), they will probably never need changing.

When your diff gets rough and feels “notchy” it is generally not the balls or thrust rings that are at fault. The most common reason for bad diff action is the failure of the outer hub bearing. I will discuss this in section 3 below.

2. Feelin’ Groovy



First I take the polish out of the surface of the thrust rings. Find a flat surface and lay down a sheet of 600 grade wet and dry abrasive paper. Work the D ring around in circles on the abrasive paper until you have a consistent finish around the orbit that the balls will travel. This is not new info here and the IRS site suggests this approach http://www.teamirsrc.com/techtips.html

The thrust D rings are pressed out during manufacture and you will find most of them are slightly concave. You will notice this when grinding them on the abrasive paper. The side you want to select to run against the balls will be the side where the grinding wear starts on the outer diameter of the ring working in rather than from the centre working out.



Before and after surface preparation

Ceramics



Ceramic Balls Fitted.

If like me, you go for the ceramic balls, I have found that these may not grip on the thrust rings when brand new. The ceramic balls are so hard that they can just skim over the surface of the thrust rings resulting in less diff “grip”. If you are not careful here you can make the mistake of over tightening the diff to prevent slipping and damage the outer hub bearing.


The way I fix this is to build up the diff with a smear of “T Cut” car body restorer temporarily used in place of the silicone grease. T Cut is a light abrasive liquid suspension. Apply this to the thrust rings and the balls but do not get any in the centre ball race that locates the spur on the axle (or anywhere else other than the balls and thrust rings).





Lightly tighten the diff, just enough to get some diff action. It is going to feel a bit nasty… it’s full of T Cut! Now start to work the diff by hand for a few minutes. Force the spur gear around a few times against the action of the diff. While you do all of this, the T Cut abrasive is causing the ceramic balls to form a fine groove in the thrust rings. The surface area of the ball to ring contact patch is being ground in and increased.



Photo above shows ground ring contact patch.

After 5 mins of working the diff by hand, strip it down and clean out all of the T Cut. You need to remove the balls and wash out every trace of T Cut . Degrease the balls, rings and spur gear with motor cleaner. Rebuild the diff with a fine smear of silicone diff grease on the thrust rings and try it again by hand. You should now be able to achieve acceptable diff “grip” with much less thrust tension.

3. The Outer Bearing is the Weak Point

Now… the standard diff balls you get in the kit tend work well from the start, the ceramic balls may need to be “ground in” (above) but once prepared, they will last you all year. Either way, when your diff gets rough it is generally not the balls or thrust rings that are at fault. The most common reason for bad diff action is the failure of the outer bearing located in the diff hub.

As we tighten the diff, the thrust load is applied to the balls and rings via the outer hub bearing. This bearing was never designed to take this kind of lateral force. This misuse is bad enough but it is made worse when you hit the boards with your rear wheels and send a shock load to the already compromised and stressed bearing.

My advice is to use a ceramic bearing on the outside of the hub, again from http://www.rc4less.com/ see http://rc4less.safeshopper.com/22/386.htm?32

I have found that my diffs build up smoother and last for longer using this bearing. Unfortunately you will still have to change the bearing out every forth meeting or so to preserve optimum diff action. If you take a big hit on the rear axle, the outer bearing can still fail at any point, even if you do use a ceramic.

I was around when Cecil Schumacher invented the ball differential (yep I’m getting on a bit ;-) This was at a time when 1/12th scale was the only electric racing class. The original Schumacher ball diff used a thrust race on the inside of the wheel and did not place any lateral loads on any bearings (hmmm to be honest I don’t think it had any bearings!).



Slapmaster Thrust Race Fitted (more later!)

Next I would like to review the Slapmaster Tools thrust race that can be added to the Associated type diffs that we all use today. This upgrade removes the lateral load on the outer hub bearing and creates a diff that will last “forever” (apperently!). More on this later, I hope to test this part at our UK worlds warm up meeting and I will report back.

Going Brushless; Report from 1/12th Scale 2006 European Champs

Going Brushless: Report from 1/12th Scale 2006 Euros

During the 2006 European 1/12th Scale Championships in Gran Caneria, I had the chance to test out the new LRP Sphere Competition Brushless ESC in combination with the LRP 4 Star Vector Brushless Motor.



For more information on the 2006 1/12th Euros see http://www.ec2006.org/
For background spec and technical info on the LRP Sphere/Vector Brushless system see http://www.lrp-electronic.de

Currently in the UK 2005/2006 season, BRCA sanctioned events for 1/12th scale do not allow the use of Brushless systems. As a result of this not many UK 1/12th racers have gained any significant brushless experience so the Euros were going to be a watershed.

The Base Modified setup

I arrived for the Friday practice sessions with my standard setup for modified loaded into the car. I use a KO VFS Competition ESC with various motor options. My most used motor has to be the Corally Black Series 10*2. This motor seems to have the best run time for me when timed around 11 degrees and pulling 40mm/rev.



As you can see, the brusless setup is 28 grams heavier than my modified brushed setup.

Drive Smooth

By nature I am a smooth driver. I tend to not throttle jam and being a bit of an “old man” I like to allow the car to roll around for the first 2 mins at least. I will use the sweeper at the end of the straight to save energy and try not to feel the end of the sick too much until the last 4 mins.

End of Season Cells

We all know that cells loose capacity as they age with charge/discharge cycles. I must admit that I aimed to compete with “end of season” GP3700 cells. These cells have lasted me the whole UK BRCA national series running both 19T and modified events.

I do keep an eye on things and I know that from testing all my packs prior to the event , they charge to around 4200 mAh (4.5A charge 0.04 pack delta on a ProTrak charger). Discharge capacity for the 20A cycle on the Protrack is in the order of 3600 mAh (0.9V per cell cutoff). Hence these cells are not the best but they are not garbage either.

Run Time Issues

As the grip came up during Friday practice and by the 4th round with my brushed setup I started to dump! It became obvious to me that run time was going to become a major stress for me.

After the first grading round I was 21st overall (this was not going to last! I am one of those drivers cursed with the ability to drive a new track reasonably quickly but then not improve!)

The Euros track was as large as we see on the UK scene with the top pace being around 37 laps.

I realised that my duration situation was just going to get worse…….

LRP to the Rescue!


I had already arranged the possibility of testing the LRP Sphere/Vector system in association with Helgar Racing (the UK distributor of LRP) and LRP. The LRP Company had Reto Konig (R&D Manager at LRP) in attendance giving technical support to drivers at the meeting.

Reto hooked me up with the Sphere Competition ESC and the 4 Star version of the Vector brushless motor. I only had the time between adjacent timed practice rounds to fit the combo to my CRC Carpet Knife!

Fitting the System

Reto had already fitted a thinner 16 AWG wire loom more suited to 4 cell 1/12th scale cars. None of us would want to run the 13 AWG wire that the system is supplied with (suitable for TC racing), there would be too many tweak issues to the Motor pod on a 1/12th scale car.

The ESC also had a small 470uF 16V power capacitor pre fitted to small power wires coming from the side of the unit.

My first fitting attempt was a failure (!) mainly down to me rushing to get the car turned around for the next qualifying session. Less haste and more speed was required.

In the end I settled for the layout you see in the pictures with the sense wire running under the tweak brace and the three motor power cables following the centre line of the car.




LRP make the sense wire in two lengths (Part no 81920 is 100mm and 81910 is 200mm). I had the shorter 100mm harness which is just right but only just long enough, you have to fit the ESC as I have shown or the short sense wire will not reach.

I made sure the motor wires did not obstruct the damper tubes, restrict rear pod movement or catch on the underside of the body in any way.

The LRP Sphere Competition controller is the lowest profile brushless unit available and does not need a fan or heatsink for 4 cell 1/12th cars. This is good news as it just fits under the Parma Zytek shell that I tend to use. This shell is one of the lowest shells at the sides so if this works for me it will work for any body I think.

I just managed to turn the electrics refit around in time. The rest of my tyre and car prep was a bit of a disaster due to time pressure but I managed to do it all in the one hour available. To be honest, people have said that fitting brushless to a 1/12h car is a stress, I did not find this to be true. Give me two hours not under meeting pressure and I would have a neat job done and time for a cup of tea and a sandwich.

The Basic Settings

The Sphere programming user interface is similar to the Quantum QC3 and Nosram clones so it was familiar to me even without the manual.

Reto had preconfigured the speedo with the following settings which I did not change.

Mode 1: Auto Cell System Setting 2 = NiMH 4-7 Cell racing mode
Mode 2: ADPC Power Profile Setting 3 from 6 Levels increasing punch
Mode 3: Initial Brake Setting 2 from 6 Levels increasing initial brake
Mode 4: Automatic Break Setting 2 from 7 (0-6) Levels increasing drag break

I don’t use breaks in 1/12th scale so the Mode 3 setting was irrelevant to me. This is not true of the Mode 4 setting. Brushless motors do not magnetically “cog” so it is important to simulate the natural breaking of a modified motor to create the same weight transfer and slowing as you lift off the throttle. LRP (Reto) advised me that the Auto Brake setting of 2 would be like a “standard” modified motor so I went with that.

Gearing

I was advised to start at 30mm/rev (wow.. that’s low!) so I did exactly that. I had to buy a few new pinions and ended up on around 21/96 on 45mm dia tyres. Remember that this is the 4 Star motor here.

In Use

I took it easy for the first two laps…. Then started to push….. oh its fast! Feels like my 10*2 … more top end speed with a really smooth power delivery. The auto break felt no different to my brushed motor and I was straight onto my previous lap times.

So… after 4 laps I decided to “drive it like I stole it” just to see what would happen. I nailed the thing for the remaining 7 mins. It was not pretty and I am not proud of myself ;-) but I had a lot of fun.

The car just ran and ran to the end. I lifted it off the track and the motor was warm but not hot to touch. The post race discharge (now there is a novelty) showed me coming back with 300mAh left in the tank. Oh Joy.

Now…. through Saturday (qualifying) and Sunday (finals) I did not touch the motor or even think about it. I did not dump once and in fact, I won the first leg of my final (from 5th) in the last lap as the leader dumped in front of me ;-) I had legs to the end.

After 3 legs I was 3rd overall in the D final. Not bad seeing Marc Rheinard had come out to play with the CRC trinity and the 12 disciples thrown in for good measure.

In hindsight maybe increasing the Mode 2 power profile from 3 to 4 may have been interesting .. oh well, next time.

Conclusion

To my mind the LRP Sphere/Vector Brushless system is a total winner. I spent an enjoyable two days of competitive racing at the Euros without the anxiety of dumping and I did zero motor maintenance.

I was left in peace to think about racing lines, car setup and tyre choice.

It is true that the top three cars in the A final (Team CRC!) were running brushed motors and maybe it can be argued that with brand new top class cells and Oscar Jansen sat at your pit table brushed is very fast indeed. I am mature enough to realise that my failure to make B and A finals at this level has nothing to do with horsepower. I am simply not good enough, and this may never change. I just want to keep on learning and enjoying my racing. The Sphere/Vector combo just added to my enjoyment of the whole weekend.

I really hope we pass Brushless for the 2006/2007 BRCA season. I know how I will be voting.

In preparation for the last UK modified national at Chesterfield I have taken the LRP system out again and it is sitting in front of me without a car. Oh well. Better charge the comm lathe pack again……

Many thanks and regards to

Helgar Racing http://www.helgerracing.com/
LRP Electronic http://www.lrp-electronic.de/
Reto Konig
David Splashett

Preventing and Repairing Rear Tyre Chunks

Preventing and Repairing Rear Tyre Chunks

One of the things I like about 1/12th scale racing on foam tyres is that the grip remains consistent independent of the age of the tyres or the number of runs they have done.

In the UK we only run odorless additives which are less aggressive to the rubber, the track and the health of the people at the meeting! I have completed a whole meeting on one set of foams for example. Readers of this article may want to argue about the benefits of rotating to a fresh set of tyres every run within the racing day to prevent the tyres from becoming over soft.

My objective in this article however is to demonstrate how “chunked” rear tyres can be prevented and even repaired. Tyres are expensive and I hate the feeling when you come back from a heat or final with the outside edge of your precious foam rubber with huge bites out of them.

All it takes is a little care and time. You can save yourself some serious beer money!

Preventing Chunking in the First Place

Well the first rule is not to hit anything and do not get hit! Failing this, tyre checking and maintenance is going to be required after every run.

In general only the rear tyres will have chunks ripped out of them. The fronts normally come back chunk free but it still pays to check them over.

Try to peel back the tyre from the wheel on the outside edge using pressure with your finger or thumb against the side wall. If there are any gaps developing between the tyre and wheel (even small ones), you must repair these now. Failure to do this will result in further damage in this “peel” area and eventually whole bits of the unsupported foam rubber will be ripped away from the tyre resulting in the dreaded chunking.








Use the right Glue

Squeeze some contact adhesive (I use Evostick) into the gap and then work it around with the end of a knife or miniature screw driver. Do not use superglue! With foam tyres we need glue that will flex with the tyre. If you use a super glue or cyano type adhesive you will create hard spots in the side wall and the tyre will rip around these spots again.

If you have made a large repair, it might be a good idea to apply some light pressure around the outside of the tyre while the glue sets. I use a strip of “Velcro” to do this but a rubber band will do just as well.



Leave the tyre for a good 30mins before you run it again.



Chunk Repair

Ok, when I explained this trick some of my racing friends; they simply did not believe me! So I have laid it out for you step by step. Unlike my most of my "improvement targets" in the A final , I do not get given tyres so this is all very important to my wallet!

To do this level of repair you are going to need a a tyre truer, a scapel knife, Evostick type contact adhesive and some nasty chunked rear tyres. I persnally find I have the latter in plentiful supply.

You will notice my patient tyre has two nasty chunks which I will repair at the same time (because I am that good nurse!). These chunks are quite small but to be honest, the smaller ones are harder to repair.






Step 1

Glue under any gaps between the damaged wheel and the damaged tyre. There may be small tears in the tyre that you are left with so you need to repair these with contact adhesive before we move on to addressing the bits of foam that are missing.

Step 2

Choose a donor tyre. This needs to be a scrap tyre of the same compound as the one under repair. It also needs to be slightly larger in diameter than the current patient also. This one donor will repair many patients!

With a scalpel knife carve a chunk out of the donor tyre that is a similar shape but slightly oversized compared to the missing bit in the repair tyre. You will be surprised just how bad this match can be! Providing it is “sort of right”, we are going to be able to cram it on in there later! Try to match slants and features in the patient’s “hole” buy cutting these features in the donor chunk. Again do not worry too much but do make sure the donor piece is oversized.




Step 3



Apply Evostick contact adhesive to both the surfaces of the chunk hole in the patient tyre and the donor repair chunk. Make sure all surfaces that will finally come together when the chunk is pushed into place are well coated.

Do not over glue here. We are looking of a shiny glue finish on both parts. Wipe off excess glue. Do not bring the pieces together yet! We need to glue to dry off. This will take around 5-10 mins. Go make a cup of tea.

The idea of a contact adhesive is that the two parts are “tacky” dry before we bring them together.


Step 4

Now fix the repair piece into place. You only get one shot at this:

Hold the repair piece over the hole with slightly too much material than will fit, ready to be pushed into place. Start the contact point from the outside rim of the tyre working in. Really compress the repair piece into place. The contact adhesive (if dry enough) will grip it and hold it fast.

Now wait again. A good 30 mins is needed for the glue to go off. Go make a sandwich!









Step 5

A disclaimer, especially for my international friends some of which have a certain reputation for “compensation culture” attitudes….. Placing your hands near fast spinning objects is dangerous. Do not attempt this unless you are a consenting adult and you have assessed your own risks. I take no responsibility whatsoever!



Place your tyre on your truer and wind the tool in over the repair area until it just starts to cut the oversized replacement chunks. Slowly grind these down until you are at the same diameter as the rest of the tyre. Take a final small cut on the whole tyre.




Now using glass paper, true the side walls very slowly cutting back the protruding repair chunks until the side wall is flat.

Finally round off the edge of the tyre with a small radius as normal.




Congratulations! As the before and after images show. You just saved yourself the equivalent of £14.

Cheers

Mark Payne

CRC Carpet Knife 3.2R Total Tweak Guide

Total Tweak Guide for the CRC Carpet Knife 3.2R

Essential Reading and Prerequisites

In my previous posts on statically balancing the CRC Carpet Knife, setting good ride height and correctly building the Associated reactive castor front end, I was trying to lay the foundations for ending up with a totally tweak free car.

The following three articles are hence prerequisite procedures before moving on to the steps detailed below:



Please note that I only have experience of the CRC Carpet Knife 3.2R. Obviously the Associated front end is common to many cars but my total “system” assumes you have rear pivot ball and side spring type rear end.

Read these first:

http://markpayneblog.blogspot.com/2005/12/building-associated-l4-type-front-end.html

http://markpayneblog.blogspot.com/2005/12/crc-32r-chassis-setup-static-balance.html

http://markpayneblog.blogspot.com/2005/12/measuring-ride-height-on-crc-32r.html

The Coin Trick is Not Enough

Most people use the coin trick on the front tyres whereby you lift the front off the ground via the front center point and adjust rear tweak screws for a simultaneous coin drop. In fact I will end this article with the coin trick as a final tweak check BUT… the validity of the “coin trick” is dependant on other things being right first.

With the coin trick, what you are doing is setting the rear tweak screws to equate the downstops (limit of upward front suspension travel) of the front suspension. This is a factor of how accurate the front lower arms are and the ride height spacers included under them. Why would we set the tweak on the rear springs to fix a potential error in the front arms? The rear tweak should adjust the springs when the chassis is LOADED onto the springs all round, not unloaded at the front.

Don’t worry… if you don’t get this yet… we will go through the whole thing here.

Lets Start

I am assuming you have done the following checks (read the previous posts above):

A. You have a well built front end with all the slack just shimmed out of the king pins.

B. You have a fresh ground set of accurate and equal tyres on the car. The left and right tyres are exactly the same size measured with your calipers.

C. You have set the ride height to 4mm all round using the “five points” system.

Step 1

Remove the whole rear tweak bar assembly and damping tubes. We will be setting up the front end first. Load the car with a set of cells. You will notice that I tape cells into the car. I do not use the CRC “rubber band” cell retention as I believe this can tweak the car.

Now that the tweak bar is off, it is a good time to check the chassis pod is rotating freely. When a CRC car takes a crash, the centre pivot plate can be shifted out of line causing the rear pod action to bind. I now tend to check this every run at important meetings.

Video: Checking Pod Movement

If in doubt, loosen the two pivot plate screws and retighten them with the pod aligned with the main chassis. Recheck the pod action again.







Step 2

Spend some time and make sure the camber on the front wheels is set to 1 degree and is the same left and right. I use a protractor that I have had since my school days (its old!) but there are plenty of camber gauges on the market.



Step 3

Take the front wheels off.
I put the chassis on 5mm blocks. Hudy make these http://www.hudy.net/xhudy/products/proddesc.php?prod_id=153&kategoria=64


Make sure the chassis itself is on the blocks and not any protruding screw heads, cells or cell tape. If the blocks are parallel to each other there should be no “rocking” evident. If the chassis rocks on the blocks then it is twisted. You will never tweak this car out with a twisted chassis.






Now use your calipers as shown to make sure the front axles are at exactly the same height off the glass. If they are not I grind the front A arms until I have the a perfect match. If you have followed my previous front end instructions then there should be no issues here and this is just a sanity check. If the axles are not at the same height to within 0.25 mm (0.01 in) then you have a problem that you must address.

Step 4

Put the rear tyres on (fresh ground). The rear tweak bar and side dampers are still removed. The centre shock and spring is on as normal.

I now place 10mm blocks under the front axles (ok, I use whatever I have at hand to make an accurate 10mm block). The rear end cannot impose any tweak on the chassis as there are no side springs. Even if there is a slight error in the rear tyres, this cannot be transferred through to the front end. The lateral balance of the chassis is now purely a function of the front springs only. You statically balanced the chassis already right? (I do hope you have read the prerequisite steps ;-).


Something to be aware of … we balanced the chassis as a whole earlier but right now the front springs are subject to the full running weight of the car but the weight balance is being imposed by the front part of the chassis only.

I asked myself .. “ what if there is a balance error in the rear pod that we correct in the front (main) part of the chassis?” … Let me save you some time. I took the rear pod off and measured it’s balance complete with motor and pinion etc, it is crack on. An engineering thing that Calandra have got 100% right.

Step 5



Now with the chassis loaded onto the springs at the front, any left/right differences in loaded spring length will result in the chassis not being laterally parallel to the glass. This error will be maximized at the back of the main chassis near where the tweak mounting pods are attached; this is where I measure using a “wedge” type ride height gauge.



Add or remove one or two king pin shims until the left and right reads exactly the same. You will be taking a shim out on the high side or placing a shim in on the low side.

Assuming you (just) shimmed out the slack in the king pins earlier, if you now have to add or remove more than two shims on either side to get things right at the back… alarm bells should be ringing. Something else is wrong here. Go back and check the build of the front end (separate post) and the previous steps in this section.

I generally only accept the addition or removal of one shim on one side or the other at this point to level things up.

Step 6

Its time to put the tweak brace back onto the car. But before we do this I have some tedious details to discuss!

Motor Wire Warning

Be careful. The wires going to the motor can tweak the rear pod, resisting it’s free movement. To help with this I use 14 AWG wire, not the 12 AWG I have in my kit from 1/10th scale touring cars!

I take the wires under the tweak brace. If you go over the top they can catch on the body, again introducing tweak.

Which Side Spings?

I generally use the red side spring as a starting point. I go to the white spring (softer) for less direct steering. There are two main things I have learnt about adjusting these springs.



The first point is to make sure the spring sits on axis with the tweak screw and mounting. If it is off centre, you get unpredictable changes as the tweak screws are adjusted.

Now attach the tweak brace and I will come to the second point:

Start with the tweak screws wound right out (springs tight against the brace). Now wind down the same amount on both sides until the springs just touch the balls. I have read CRC setup notes where it has been recommended that this is how you should run the car. Ie. With the springs just resting on the balls when the chassis is flat. But…. My second main point is that I have found the car much more predictable if I load two full turns of spring tension beyond the “touch down” point.


Leave the side dampers off for now. The front end is still on the the 10mm blocks.

Now look from the rear and lift the rear pod off the ground using the centre point. I adjust the rear tweak screws to ensure both REAR wheels lift at the same time. If you are adjusting the tweak springs by more than ½ a turn on either side, alarm bells should be going off again. Go back and recheck everything because something is wrong.

Step 7

Now look from the front and sanity check the action of the front suspension. As you lift and release the suspension up and down using the centre hole at the front, you should see the same spring compression and expansion working equally on both sides.

Video: Comparing Left and Right Front Spring Action

Well done! You car is now corner weighted and applying balanced pressure left to right.

Step 8

Now comes the “coin trick”!

Why are we doing this?

To be honest, if you have carried out all the steps above, you don’t really need to do this. Remember your car is tweaked out evenly on the springs and the “coin trick” is going to lift the whole front suspension off the springs. Is this how the car drives? I think not. You already know the front axles lift off at the same height, because you checked this at Step 3.

However, assuming that you have laid the foundations by doing all of the above, the “coin trick” is the quickest way of re-tweaking the car to allow for the errors that creep into the tyre diameters after a run. No track imposes even left/right tire wear and we have to reset for this each run.

I swap the left and right tyres over each run to balance the wear rate up. After doing this I will re-tweak using the coin trick rather than do through the total “system” from scratch.

The Coin Trick

UK readers will want to find two 20p pieces or two £1 coins if you are feeling rich! As the CRC CK 3.2R is such a well engineered American car, I like to use $1 coins….. also this prevents me from spending my tweak tools at the tea bar on race day :-)

Attach the front wheels (fresh ground, the same size!) and place the car on your level flat surface.

Now place your money on the top of both front wheels, just slightly beyond the apex (by the same amount). Now lever the car up using the front centre hole s l o w l y.
The wheel that lifts first will drop the coin first. This is the high side.

Video: Coin drop on a car with bad tweak

Correct the high side (coin dropped first on the left here) by winding the tweak screw down on the opposite side (clockwise turn on the right in this case). Alternatively back off the tweak screw (anticlock) on the same side as the “early drop” coin. Adjust by no more than 1/8th of a turn at a time. If you are using more than ½ a turn either way then something is wrong or it is time to re-true your tyres.


Video : Coin Drop with good tweak

Conclusion

If you join me at this point then I congratulate you! You are as “sad” as I am :-)
… but I am confident that you car is going to go straight when you power up!

Happy racing!

Building the Associated L4 Type Front End

Introduction

I use the Calandra CRC Carpet Knife 3.2R but the following build note apply to any car using the Associated reactive castor "L4" type front end.

I am heading towards explaining how to fully tweak out the CRC Carpet Knife 3.2R chassis. Before we look at the final tuning of the whole car it is important that the Associated front end is built as consistently and accurately as possible.

Get it right!

Fractional errors and “left to right” differences in spring lengths, shimming, block moldings and general alignment within the front end will cause unpredictable handing on the track.

It took me a whole season of 1/12th racing to realise that the driving the car is hard enough on its own without the thing wanting to pull right or left under acceleration. I am not an “inch perfect” driver but I am learning to build and inch perfect car. Unfortunately, predictability measured in inches on the track needs accuracy down to fractions of a millimeter or 1/100th of an inch .. or better!

You are going to need a set of vernier calipers to make the required measurements. I use a digital one from Mitutoyo http://www.mitutoyo.co.jp/eng/products/nogisu/hyojyun_01.html

Step 1 Checking the Lower Arms

Using your flat surface (I use a 2.5 sq ft safety glass offcut), make sure the Associated left and right lower arms are the same height. You will be surprised how different these things can be. I have had two arms from the same packet as different as 1mm (0.04 in).






If there is a difference, you will need to “grind” the high one down until they match. To do this, lay a new flat piece of 200-300 grade abrasive paper on your flat surface and apply an even pressure, keeping the molding parallel to the surface. It is important that you do not grind an angle into the block as you remove the material.



In measuring here, the critical height is from the glass plane to the upper surface of the arm where the ball gets inserted.







Step 2 Choose your balls

I have found a much better king pin pivot ball than the standard kit part.
The suspension balls I use are Teflon coated. You will end up with a much freer suspension using these parts while keeping the suspension free of play.

http://rc4less.safeshopper.com/22/389.htm?692

I think IRS do these also. Not cheap but worth it… trust me.



Finally, when you push the balls into the moldings, make sure the collar is orientated towards the steering block. The collar will be pointing up in the lower arm and down in the top ball joint.

If you use pliers to force the balls into location, do use some folded paper to prevent the pliers from causing damage.

Step 3 Trim the lower arms

If you use the CRC front axles (as I am sure you do.. the titanium ones are great!) the securing nut on the inside of the front block will hit the lower arm on full lock so some trimming is needed here. The two photos below show this trim.



Also when the suspension is built the steering block must ride top and bottom on the metal pivot balls, not the lower arm or the upper ball joint plastic moldings.

The castor of the steering block (as a result of the king pin angle) tends to make it bind on back edge of the lower arm while steering, lifting it off the lower ball. To stop this, trim some material off of the lower as shown.











Step 4 Polish the king pins

It’s a simple thing to do but it makes a real difference to the feel of the suspension. Make sure the king pins move freely in the pivot balls. I use a house hold metal polish to do this. After polishing it is important that all residue is removed. If you fail to do this the polish grit itself will become a binding agent in your suspension.

The king pin may be burred where the slot for the E clip has been machined. This makes the king pin slightly oversized and it may scratch the ball as you push it through. A light touch with abrasive paper around the ends followed by a polish will solve this problem.

The king pin moves through the lower arm ball like a piston as the suspension compresses on the spring so it is important to make sure this area runs especially free.

It is also important for the king pin to move freely through the steering block. I use the optional Delrin CRC block. This is more accurate than the stock Associated molding.

http://www.teamcrc.com/crc/modules.php?name=Shopping_Cart&file=product&c_op=viewprod&prodID=7718834

… the reaming for the king pin is really nice and free… but…. There is a problem here. The Delrin blocks include stock axles but if you screw in the CRC threaded axles, the king pin hole tightens up and the suspension will bind.

After screwing in the CRC axles it is necessary to ream out the king pin hole to an accurate 1/8th fitting again. You can do this by hand using a 1/8th drill or (even better) a 1/8th reamer. Alternatively, just stick with the stock axles that come with the blocks.

Step 5 Polish the upper pivot pins

I have started to use the CRC optional Delrin upper arms as they are more accurate than the standard associated ones.

http://www.teamcrc.com/crc/modules.php?name=Shopping_Cart&file=product&c_op=viewprod&prodID=7718833

The upper pivot pin can bind on these arms, mainly because the tolerances in the pivot hole on the CRC part is tighter.



Polish the pivot pins, especially at the ends where the bearing surface is made with the upper arms. You do not need to get the pin to run free in the reactive castor angle block (the 0 degree, 5 degree, 10 degree part), you will probably want to lock the pin in place with a grub screw here anyway to hold the pin fast.

When assembled, the top arm should pivot around the pin with no noticeable friction, damping or binding.

Handling note

I normally run the 10 degree reactive castor block which does offer the most aggressive steering out of the three (10, 5 and 0 degrees). I will reduce to the 5 degree block if the car is too snappy on the front.

Step 6 Shim and Spring the King Pins

Handling note

My starting point is to work with the 0.020 in. front spring. The spring number is referring to the diameter of the wire used to form the coil. The higher the number, the thicker the wire and stiffer the spring. Optional springs are as follows:

0.018 in. Soft
0.020 in. Medium
0.022 in. Hard
0.024 in. very Hard!

Spring Errors



First pick two springs with the same thickness and measure them with your calipers to double check yourself. I know this sounds stupid but I have made mistakes in the past and ended up running different springs left and right!

It is also important that both the springs are the same length to within 0.01 in (0.25 mm) which is the thickness around two shims. If the springs differ by more than this I would assume that one has collapsed and is damaged. Get a new pair.

Adding Shims

I like to shim the king pins so the play is just taken out of the assembly when there is no load on the suspension. The shims are applied to the top of the king pin between the top ball and the upper E clip. Do not use motor shims as their outside diameter is too large and they will bind up in top ball joint molding.
The correct shims for this job have an outside diameter of 4.92mm (0.1940 in).



The two shims sizes I have are 0.11 mm (0.0045 in) and double that at 0.22 mm (0.0090 in).

If you use the Teflon coated balls (as mentioned above) with the 0.020 spring and have trimmed the back part of the lower arm also, a good starting point for the shim stack is 2.22mm (0.0870 in). The problem with giving this measurement is that there are so many variables including the balls, steering arm, king pin length and even the E clip thickness.

Step 7 Final Check

Finally mount the front end on the car.

Adjust the servo links for Zero degrees toe. Then use a camber guage to get to set 1 degree of negative camber.

Always remember, when using the turnbuckles to adjust the front camber, ensure the top ball joint part finishes inline with the king pin. That will mean that it is angled back slightly.

Finally check that the shims have just taken out all of the king pin play and that the suspension has the same free feel when you compare left to right.



Cheers

Mark

CRC 3.2R Centre Shock, Spring and Pod Droop

Centre Shock, Spring and Pod Droop



The VCS centre shock and its spring controls the “bend” in the chassis (around the rear pivot point) when power is applied by the motor. Under throttle this spring is going to compress. It will also compress over the bumps.

There is no limit to the compression of this spring other than the chassis bottoming out. I guess you could fit a limit cylinder on the shock shaft but I have never tried this. My gut feel is that the compression evident with the car on the track is a few mm at most.

We do however limit the backward movement of the pod using the length of the VCS shock and its ball joints. The trick is to get the shock length just right according to your required backward movement. This back tilt allows “lift” in the chassis height above the static setting, maximised around the cell area.

I have read recommendations that this allowed “lift” should be around 1mm, however, I have been tuning for no lift at all. I find that the rear end is more predictable this way.

Broken Shocks

The pod back tilt or lift is limited by the shock shaft itself. If you tune for no lift or only 1mm, a crash can cause the chassis to pull the innards of the shock out, which is not good! With the standard Associated VCS shock, the only thing holding the shock together is the plastic “E” clip.

I have started to use the CRC Dura Shock which solves this problem http://www.teamcrc.com/crc/modules.php?name=Shopping_Cart&file=category&category_id=24

I have never had a crash failure with this type of shock.

Improving Shock Balls

Removal of the battery pack can require the removal of one end of the VCS shock. I see people in the pits killing the ball joints with pliers. This cannot be good for the reliability and accuracy in this area.



I use the threaded stud type of ball joint used on XRAY touring cars. These are the 303220 and 303240 parts found here:
http://www.teamxray.com/teamxray/products/proddesc.php?prod_id=394&kategoria=1290

Measuring ride height on a CRC 3.2R

Measuring ride height

Before we can do a fine adjustment on chassis tweak we need to get the basic ride height and rear pod droop set roughly right.




I measure ride height in 5 places as shown in the pictures. These 5 locations tell you a lot about the car. You will need a “wedge” type ride height gauge, not a stepped one. The wedge gauge will allow you to measure ride heights to within 0.2mm. This is the one I own: http://www.hudy.net/xhudy/products/proddesc.php?prod_id=157&kategoria=64

A word about chassis rounding: I notice many people round off the edges of the chassis for a smooth look. Yes ok, this looks nice but you loose the accurate edge against which you can measure ride height…. So I don’t bother.

As you can see in the pictures (4mm ride height intended), I expect to be able to tweak the car out (full instructions later!) and end up with a ride height that is equall from left to right within 01. to 0.2 mm.

Starting Tyre Size

Accurate ride height and setup can only be achieved if you have accurately ground tyres. A good starting point is with 50mm rears and 45mm fronts on the CRC. I like to race nationals with tyres much smaller than this but I start here for club meetings. If you don’t have access to a tyre truer then your ability to set up a 1/12th car is going to be severely limited.

True your tyres and use the rear pod axle spacers and front block shims to get the ride height around 4mm as a starting point. I tend to run ride heights between 3-4mm depending on the quality of the track.

A warning about front block shims.

I use the Fibre Lyte shims http://www.fibre-lyte.co.uk/fl/cars/callandra/calspa.html
The idea is that you can push in the shims in just by loosening the front block screws but there are problems here.

I have found that the “U” shape of the shim allows the block to distort into the open part of the U…. and no, I do not over tighten the screws. This leads to unpredictable geometry at the front.


Bad Good

My solution is to cut the shims into four separate “U’s” and turn them through 90 degrees so the block material inboard and outboard of the screw is supported.

CRC 3.2R Chassis Setup. Static Balance

Chassis Balance

Tweaking out the chassis for predictable handling on a 1/12th car is going to be dependant on a good static balance from left to right as a starting point.

Start with a flat surface which is level on your workbench. I use a piece of safety glass (pop down to your local glazing company for an off cut). Level the glass out with a spirit level.



The chassis will need indentations or small holes at the front and back on the centre line of the car to allow the correct location of balancing pins. The rear hole needs to be located on the back cord of the rear pod. I cannot remember if the CRC rear bottom plate has this hole and the front definitely does not.

Use a set of calipers referenced off the inner edge of the rear wheels to find the centre line of the rear pod, the whole pod is off centre so this is the only reference that makes sense. The centre line at the front is easier to scribe from the edges of the chassis.

Now comes the balancing bit

Set the car up with all your gear, wheels/tyres on and set for correct ride height and rear pod droop (more on this later). Batteries in, pinion on and wiring all plugged up ready to go. Just don’t stick any of your electronics in yet.

The variable items that can be moved around will be the speedo, radio receiver, RX battery pack (if you use one) and Personal Transponder (PT). I place the PT last to fine tune the chassis balance by moving it between the steering blocks at the front.

I have made a pair of alloy balancing pins which locate into the holes made earlier in this discussion. HUDY make these things if you have need http://www.hudy.net/xhudy/products/proddesc.php?prod_id=173&kategoria=64




Place the car on the pins and use a spirit level over the back tyres to locate the car parallel to your flat surface. Now when you remove the sprit level, the car will obviously fall over on the heavy side. You can now move your electronics around until the car balances perfectly on the pins.


Finally locate all your gear and stick it down. You are now ready to move on the next part of the chassis setup.

Brushless Update Nov 2006

Here we have a problem, the approach above is valid for your brushed modified and 19T motors. This is becuase the rear motor pod is almost perfectly balanced with "traditional" motors. However...... brushless motors carry a weight unbalance where the pinion side is light compared to the connection side.

You may be tempted to try and correct this by shifting weight around in the font part of the chassis. This is an error in my opinion. The front part of the chassis should be statically balanced independant of the rear pod.

A full discussion of this can be found here: http://www.rcracechat.com/vb/showthread.php?t=23696 ... some of my collegues are arguing with me here which is generally a lost cause ;-) so I will reprint the main points below:

*************

Set the scene: If you take your rear pod off your car and keep it complete with rear axle, wheels, average 10 turn modified motor and pinion and then pop it in balancing posts.... it will balance (left to righ lateral balance), pretty much spot on. So.... join the car up again and put the whole thing on the balancing posts and balance it out by the arrangement of the electrics and you have a tricked out car. I have already documented this all in www.12thrc.com Now the brushless: Ooooh ... interesting (come on, if you are down this far you are interested) again my brushless post on 12thrc tell us that my LRP brushless setup is about 30g heavier than the brushed. This is not news but the balance of the motor is different. There is a lot more weight at the (I was about to say commutator end!) ... at the sensor wire/connection end, away from the pinion. This unbalances the pod. As a result, if you then correct this in the front part of the car you end up shifting weight over to the pinion side of the car. In fact, I can only achieve overall balance by adding a 5 cell RX pack right over on the pinion side. So.... I am left thinking... is this the right thing to do? When this lot sits down on the deck the front chassis is applying a slight twisting force through the tweak springs to corner weight the rear tyres. So I have decided to remove the pack which balances the front part the the chassis (take off the tweak brace and you can pivot the chassis around your front end lifting point and the rear pivot ball) but leave the car overall with an inbalance due to the pod.I think the real fix would be a modified pod with the bulkheads moved over to the pinion side (yes resulting in a shorter diff side axle offset and a longer offset on the other side). However this is really NOT an easy win.Also in Worlds brushless trim without my pack the car is at 885g (that is with my 3700s in!). The limit is 865g. If I were to run the pack and the 4300's I am going to be well over 900g.