Sunday, August 20, 2017

RC12R6 Front End Build Notes Part 2

Moving on to more build detail...

Decide your tyre diameter range

The new RC12R6 front end
The minimum front tyre diameter I will will run down to is in the order of 39.6 mm.  Starting the fronts at 40.8mm. This gives a tyre diameter range of 1.2mm .. which will be around 4-5 runs on 13.5 stock allowing for tyre wear. The ride height shim range will be half of the diameter range, around 0.6mm.

Steel shim kit and 0.5mm spacers will give the needed adjustment.
To facilitate this you will need to be playing with the 0.5mm blue shim washers in the kit and I have purchased the optional metal shims (part 4742) which are 0.2mm each (you get 4 of them in the pack).

The design of the low blue stand off mounting the lower carbon wishbone to the chassis will allow for very small front tyre diameter... down to and beyond the rim if you like!

The reality is that you will be always using the 1mm spacer so why not mount that on top so it is secured in place always.

1mm blue shim always on top of the standoff
The standoff is not deep and takes thread from both sides. The lower side against the chassis will see the most action as continuous adjustments are made for ride height.
Size the top screw correctly.

If you are not careful the screws will meet each other in the standoff before clamping down so watch out!

I ground 4 top screws to 8.25mm to allow enough thread free in the bottom when using a standard 5mm CSK to go up into the standoff from beneath the chassis. This length will allow the perminant location of the 1mm spacer as shown above. 

Consistent front ride height.

I have not changed the approach I have been using for years and this is well documented here.

I suggest giving this a good read as I will still do all of this building a car for the first time.
I have already written all the words over 12 years ago (see the link!) so here it in pictures for the RC12R6.

Hold your wishbone / stand off assemblies against each each other on a flat (very flat) surface and look to compare the ball height.

Height error seen

Mine had an error of around 0.5mm (left is high). Not good. The standoffs+Shim arrangement was not true. It only takes a tiny angle error in the standoff - wishbone mount to make this a problem outboard.

I rotated the standoffs by 180 degrees (on the axis of the screw) on one side and tried it again. This was better. Fiddle with this till you get the best match.

Once mounted on the car. Block the chassis and check the axles are at the same static unloaded height.

Which Spring?

In the UK we run on various carpets but the "ETS" black rug is popular and setup notes below will assume the use of JFT S35 compound all round.

My preference backed up by testing the car at a couple of club meetings is to run the Associated .018 springs on the front end (Part 4144). The kit spring is the 0.020 which I think is a little too hard and immediate resulting in an aggressive immediate steering response followed by washing out a little.

Eliminate almost all front end Droop.

I would recommend taking nearly all of the droop out of the front end springs. I want the car to _just_ and only just sit into the front king pin springs. As recommended in the manual I run two 8425 shims (total 0.8mm) above the steering block.

I then shim above the top king pin ball, firstly to just take all the play out of the king pin so the spring is just touching. I then add a single 0.4mm shim in addition to slightly preload the spring such that static self-weight if the car only just parts the steering block from the lower ball when the car is sat on the pit table.

Finally I set appropriate ride height on a true set of wheels. I remove the rear springs and disconnect the rear dampers. 

I then block under the front axles with 20mm Hudy blocks and check the ride height is the same left and right. 

We really should be close to within 0.2mm. I may add or remove a 0.2mm shim to change the spring preload to make this right.

When you run the car for the first time the springs will compress and you will be chasing this for the first meeting. I use old springs!

Of course I don't use 5.1mm ride height! (see right). This is the effect of blocking the front axles at 20mm.

Finally (finally) I sit the chassis flat on the board and offer up a camber gauge to the steering block to make sure the left and right castor is the same. The RC12R6 block is moulded with a nice straight edge tab that helps with this.

Of course, during this process I have set the camber to 1 degree as a matter of course. many of these steps are iterative. You get the thing built rightly and then progress the accuracy until dead right.

Finally... finally finally.... I did cheat a bit and ended up using a Xenon top ball carrier with a Roche ball in it. I fell out of love with the verticle movement of the Associated one. To be honest I am being way too picky here and would not have bothered if I did not have the bits.

Wednesday, August 16, 2017

RC12R6 Front End Build Notes Part 1

Ok, ok. I had some Yokomo blue turnbukles!

I am a little picky about front end build. For me it is one of the most important as the consistency of the way the car drives is very dependant on it's accuracy.

Lower Wishbones

First, something to get right. The front carbon lower wishbones are NOT symmetrical. There is no Left/Right to worry about but there is a front and back. This is not obvious from the manual.

Here is the manual pic below. Notice the inner mounting hole lower in the picture is more "meaty". This will be towards the front of the car. The thinner part is towards the rear. If you run it the other way around then you will have a longer wheel base than the kit setup.

We are running the kit setting here. Meaty/fatter bit forward. We are also running the kit setting for a narrow front track using the 3 dot insert as shown.

Orientate these correctly!

Thinner part to REAR of car

Fatter part to FRONT of car

Tight Ball Syndrome?
Next I feel that the lower ball carrier is too tight in the wishbone (tolerances will vary). Insert the ball and feel that it is free in the carrier. It's a nice fit and all is well but.... when I then inset this into the wishbone, the carrier is compressed and the ball becomes tight.

You don't want "tight ball syndrome" in your undercarriage, it will restrict your shaft movement later :-) Seriously. The king pin angle changes under spring compression in a reactive castor front end and this ball has to move to allow it. If the ball is restricted, it binds the king pin.

So I open it up a little with a file till the carrier is snug but not overly tight. Free your balls!

There is no way I am using the O ring supplied in the kit to secure the call carrier in place, it will move around. Follow the "racer tip" in the manual and glue it in there. I just dab a little super glue onto the flange (this is the lower side). It will capillary around and into the material joins.

At this point (before gluing!) really make sure you have orientated your wishbones so you know your left from right and top from bottom otherwise you are going to glue something in wrongly that is not coming out again without damage.

Tuesday, August 15, 2017

RC12R6 First Impressions and Build Tips.

Centre Pivot Genius

The first thing you are going to notice the the ingenious centre pivot. The pivot ball push-clicks into a holder that is then slides into an alloy surround that is bolted to the main chassis.

Associated Genius Centre Pivot

The alloy outer allows the ball carrier freedom to move forward and backward slightly without creating a locking force on the pivot. Now the rear pod has correct, unbinding rotation. The shortening effect of the side links can no longer lock the pod and a crash cannot tweak it.

David Spashett designed the Delrin "Zen Slot" for LMP cars that was a fair attempt at this idea. However I found that under a big hit this would pull itself out and damage the ball holder so I gave in on it.

The original Zen Slot

The new Associated push in ball worried me at first for similar reasons but once inserted into the alloy holder the flex needed to pop the ball out is eliminated and it is not coming out.

12th racers spend half their "sad pit lives" chasing pod tweak around so this is going to be a revelation for all.

Zen Racing have made a retrofit alloy outer that has the standard "Associated" hole centres, this is purchased with the Associated AS4728 carrier to make this solution available to most link cars.

New Zen carrier suits all cars with Associated spacing
Part ZENA118

Sunday, August 06, 2017

Associated RC12R6

Well its been a long time since my last 12th scale updates.

The Build is about to start
I have been racing on and off since the last 12th posts and must admit the influx of new, young talent in the UK has had me on the back foot! Work commitments in 2015 and 2016 very much compromised the time I could give to racing racing but the 2017/18 season is approaching in the UK and I am raring to go.

We have lovely 12th community here in "Blighty" and I am privilidged to be racing with Zen Racing and CML Distribution.

Associated RC12R6
I get a lot of people still commenting that this blog has helped them with 12th setup even after all this time so I have decided to give it a set of updates as I learn and develop with the Associated RC12R6!

Happy reading!


Sunday, November 28, 2010

Up-rated 7075 Serpent 120 Rear Pod Bulkheads from On Point Racing

On Point Car with Orange Bulkheads
 Left is Paul Ciccarello's car featuring strenghtened 7075 alloy rear pob bulkheads in orange.

The standard kit S120 bulkheads are a work of art but are not made from the strongest alloy from what I can tell. The motor side plate is prone to bending. I have had some success in bending them back but it is tricky to get right.

Comparing Standard (silver) and On Point (black) parts
 The On Point parts are available in black or orange. The rear brace is I think just the Serpent part re-anodised but the real deal is with the pod plates themselves.

The pic left shows that the On Point parts have thicker webs, especially around the motor mount holes. They are also made from the best 7075 T6 alloy.

My car with On Point pods fitted.
Paul Ciccerello from On Point Racing (USA) manufactures specialist parts for the Serpent 120L car including damper tube conversion kits, a dedicated LIPO Chassis and stonger uprated rear pod bulkheads.

Paul can be contacted at

European distribution of Paul's On Point products is via Markus Mobers at Markus is at

On Point Racing Damper Tube Conversion for Serpent 120L

Paul Ciccerello from On Point Racing (USA) manufactures specialist parts for the Serpent 120L car including damper tube conversion kits, a dedicated LIPO Chassis and stonger uprated rear pod bulkheads.

Paul can be contacted at

European distribution of Paul's On Point products is via Markus Mobers at Markus is at


It is commonly accepted that link cars have a narrower setup window compared to T-Bar cars. In the move to LIPO power we have pretty much ditched all the T-Bar cars which is a shame. It turns out it is pretty much impossible to end up with a well balanced car with the lipo down one side and the rest of the kit on the other, allowing the T-Bar in the middle. As light as a LIPO is, the rest of the kit is still lighter by some 40 grams. You cannot balance it statically and even with added weight (who wants to do that?) the dynamic balance is lost.... so pretty much every car we now see on the track is a link type.

I think the problem for the Serpent 120L was that the Mono-Shock providing side to side damping was just not working in the Link/Lipo config. Once the natural damping of the T-Bar was removed, we needed more damping from the shock and there was less moment acting on it with the reduced cell weight.

We tried to get more damping by going up in oil weight to 2000 or 3000 CST and beyond in the Mono-Shock. The result I think was a tendency for the oil to "lock" or "pack" in the shock leading to inconsistent handing and the "wheel lifting" we hate in the modern lipo/link era. Also with the Serpent Mono-Shock so low down in the chassis there is very little movement to turn into meaningfull linear damping.

... so ...By the time the 2010 Worlds came along Markus Mobers has already moved away from the Mono-Shock and was sporting a 120L with the familiar damper tube configuration. The damper tube approach holds the damping oil in shear, the damping cannot "pack". The movement generating damping is increased by being further away from the pivot point. We can get more damping with lighter oils.

Waiting for 120L Evo

As I write we are waiting for the Serpent 120L "Evo" which will incorporate this change as standard in the kit. For now I am posting pictures of the On Point Racing conversion on my car which is available now.

On Point Kits

The minimum you will need is the OP101 kit which includes 3 modified pieces of carbon, i.e the bottom and top pod plates and the chassis cross brace.

On Point also supply the OP103 Damper Tube kit (you will need to add balls and ball ends). I used these and added HotBodies balls from a HB12X (having first shortened each ball cup by 4mm).

Paul also makes the OP100 conversion kit that adds a main LIPO only chassis plate (very stiff!) in addition to the OP101 rear bits. This is drilled for a laydown servo (Futaba or JR) and will need the centre pivot assembly from an Associated R5.

Notice the OP chassis has the wider spacing for the R5 pivot. The Serpent part will not fit.

Rebalanced Motor PodThe upper and lower carbon plates move the motor closer to the diff side wheel by 1.5mm. This was a decision made by Markus Mobers I think. The idea is to better balance the pod for BL motors.

What this means is that you are likely to need a shortened outer diff hub to get the axle centred on the pod. I am using the CRC 4227 part for this. Also until Serpent come out with a new rear axle in the Evo car I use the standard IRS axle as the original serpent axle was too short.

Serpent supply the IRS axle as follows:

Now Markus is an LRP modified driver at core. He has balanced the pod perfectly for an LRP/Nosram X12 mod. However, if you run GM motors (Spec or Mod) then correct balance will be achieved by spacing the motor away from the bulkhead by 1mm. If we are going to be pedantic about this, lets be fully pendantic! We could argue it was in the right place in the first place....

 1mm shims used to space GM 10.5 motor away from bulkhead.

Build Details

I have dropped the level of the cross brace by using a pair of shorter ally standoffs from a HB12X. You dont have to do this. In fact I have packed up the outer balls becuase of this. I like a bit more room under the tubes to get the motor sensor wire through.

Also I have drilled out the On Point parts and used some Corally 3mm ally threaded inserts. You need a 4mm drill and a steady hand to do this. Of course you also need some old donor Corally T Bars to raid the studs from.

Saturday, April 03, 2010

Serpent Diff and Axle Tips


If you are using anything other than zero offset wheels then I think (like me) that you will find the short length of the Serpent axle a bit frustating. He I have pictured it next to a HB 12X axle for comparison.

We really need the longer axle to allow the use of shims to widen the rear track width when we use Jaco or Parma tyres etc. If you use the Serpent part there is not going to be much axle "meat" left in the clamping hub. My solution for now is to use the HB axle shown above. The D rings are just the same. I think the CRC axle would work also. I hope Serpent will sort this issue and change the part. Another 10mm will do the trick! Thankyou!

Watch out! Trust Race Order

Serpent have used the original (and best!) Slapmaster type outer thrust race. The manual does not explain or show that the two thrust washers are different. The inner washer has a larger internal dia of approx 4.25mm and the outer washer is smaller with an ID of 3.97mm. Make sure you put them in the correct order. The axle needs to rotate inside the inner washer without touching or binding on it. This is why it is larger in terms of internal Dia.

Notice that the grove track in each washer should face the thrust ball race. I know this sounds obvious but I have spotted people rebuilding the diff in the pits and missing this point already!.
Do it Like Slapmaster

Now onto another problem. The orange spacer that sits between the hub ball race and the inner thrust race washer could be better designed. The original Slapmaster system used a black plastic spacer that had a locating lip machined onto it. This lip centred the spacer on the hub via the bub ball race without it touching or binding on the axle that was free to rotate inside it. The Serpent part unfortunately has two issues:
1. The orange spacer internal dia is too tight and needs opening out to about 4.25mm. This is easy to fix with a Dremel!

2. There is no locating lip centering the spacer to keep it off the axle.

Left to Right: Standard Orange Serpent : Slapmaster : My Modification

hmmmm: I have two possible solutions here.

First I used my lathe to machine a lip on the spacer as shown right. Ok this is not possible for everyone and to be honest I did not make that good a job of it so....
My second idea was to super glue the orange spacer onto the hub ball race. Now this needs a deft hand, some degreasing and a very light application of cyano. Get this wrong and you will super glue up the ball race (done that! the first one went in the bin).

I have shown below a little trick using paper to ensure the oversized spacer is still centred on the axle as you bring it into contact with the ball race flange (pre-painted with a thin film of glue). Apply your thin film of cyano to the outer flange (only!) of the ball race, then slide the orange guy down the paper'ed shaft to meet it. Apply some pressure while the glue takes.
Now you can remove the paper. The hub ball race and the orange spacer should now be one and the same part. The orange spacer cannot shift to bind on the axle as it is held centre via the positioning of the ball race.
Now follow my old general diff building tips (posted here ages ago!) and you should have a great diff.

Friday, April 02, 2010

Serpent S120 Link Build Tips: Dont Tweak The Tweak Brace!

My tips for mounting the mono shock to the cross brace are as follows.
1. Make sure the alloy carriers are an easy fit onto the cross brace. Open up the the holes in the carbon if neccesary to enure the ally carriers "fall" into place without forcing.
2. Ensure the mono shock shaft fits between the carriers without any twisting or stress. The shaft should locate in the carrier indents without bending the carbon brace in any way. Work the tollerences by opening up the location holes and screw holes with a file if things are tight.
3. Find some plastic washers as shown above to clamp down onto the shaft. This will allow the shaft to seat without being twisted as you tighten down the clamp screws.

Accurate Side Spring Placement. The Tweak Bar

It seems to be the case that the correct starting point for the side spring position on the link car is to just have it touching down onto the link arms.

To achieve a predictable "touch down" it is important to have the spring's tweak screw nice and true to the cross brace. If the tweak screw goes in square to the brace then there is a chance the spring will be square to the chassis and link arm.

What I do is to use an M3 die to form an accurate positioning tool for the tweak screw.

This is laid down on the tweak brace as I thread the screw down it to ensure I start to cut the thread at right angles to the brace. A little black grease is used on the thread to aid a clean cut into the carbon.

See the result?..... Nice! If you can do this by eye, then good luck to you!

Serpent S120 Link Build: Link Love

I have two tips with regards to the chassis-to-pod link arms.

First I would advise that you open up the internal diameter of the top of the hole for the ball just a little. The ball is going to be inserted from the bottom anyway. I am taking about 0.1 to 0.2mm away here with a body reamer.

The objective is to be able to tip the link moulding from left to right without the top flange of the hole binding on the upper surface of the metal ball.

Secondly.... The link clamp screws MUST clear the material on the outside of the moulding and thread into the material on the inside. If this screw is threading into the plastic both sides of the slit then it is never going to act as a clamp.

So what I am doing is using a drill or other tool to just open up the hole on the outside of the slit so that the thread will only bite on the inside. In this way you will get a clamping action with minimal effort on the screw. If you dont do this, you will strip the fine hex head sooner or later... I have warned you!



Serpent S120 Link Build: Getting the Main Pivot Just Right

I am tring to get two things right here.
Firstly I found that the main chassis was sitting higher than the rear pod in terms of ride height. The error was about 0.3mm in my case. To get this just right and end up with a "flat" chassis including the pod, I decided to grind a little off of the pivot ball.

As a check I am suggesting that the target for the overall length of the ball and shoulder is 4.70 mm as seen below.

Secondly, in my opinion there is too much play in the seating of the ball in the pivot mouldings. I want to be able to use the clamping screws "just" tighten down onto the ball and then back off a fraction. To get this a little more accurate I am grinding away the top surface of the main lower moulding and taking some off the lip of the lower moulding to create a tighter fit as shown.

I found I needed to get the top moulding down to about 3.50mm for it to sit into the lower moulding. Remember I have also removed material from the top of the lower moulding.

Sorry if this is all a bit picky but it is in my nature!