For all the guys running the rc12r5.2 chassis , there is a transverse conversion made by reflex racing that uses a oring to hold the lipo in like a crc and includes a new shock mount that allows you to run multiple shock lengths i have been running it for about 2 weeks and it is great

http://www.reflexracing.net/RSD-AE-1...it_p_2367.html

Do you have any photos of your car with the conversion?

Hi Marc, thanks for your interest.

To all intents and purposes, the rear roll centre is the height of the rear pivot ball. Arguably the diameter of the rear tyres plays a role in this, but for all practical purposes the height of the ball is it.

You can buy a set of pivot balls that are reduced in height by about 0.5mm (but you must lower the plastic 'bridge' by the same amount, and I've never seen them sold!) to give more rear grip. That works well on low-grip surfaces.

The roll is not affected by the rear pod weight being off centre. The rear pod doesn't roll, only the chassis does. Remember the pivot in the middle of the chassis? It's there to allow the rear pod to stay flat while the main chassis rolls as the weight transfers.

That's not to say there isn't weight transfer across the rear axle; there is. That's why we said in earlier posts that dynamically it's a different ball game. That also applies to the diff, which has most of its weight offset to one side - the drive side. If we were really worried about weight distribution in the rear pod, why has no one come up with a heavier left side drive to offset the heavier diff side drive. Answer, because it doesn't matter statically! And dynamically, what we have works. It ain't broke, so don't fix it!

Don't confuse the free movement of the pivot with a mechanical stop that prevents it moving beyond a certain point - when the springs are fully compressed. During racing the chassis does't roll more than 2mm (otherwise it would touch down all the time) and that is limited more by the front springs than the rear. At that point the springs are not compressed and there is no mechanical stop in play. The chassis rolls freely from side to side as the car moves from one corner to the other.

When I am asked to help people get their car to handle, nine times out of ten the problem is a rear pivot wrongly set and preventing free roll of the main chassis. The pivot must not have any resistance or 'steps' in its movement. I usually leave about .005" of vertical play in the setting to allow for the fact that the side links are pulling the rear pod forwards and backwards when they move through their arc. HTH :)

Good stuff as always Mr. SlowerOne

Tamiya went to the extent of designing a left rear Counterweight for their F1, it floats freely on bearings

Jury is out on results of that experiment...

http://thumbs2.ebaystatic.com/d/l225...NgHL6YPdQg.jpg
http://www.tamiyausa.com/images/prod...ustom_head.jpg

Hi slowerone

Thanks for the great answer. As an engineer I am fascinated with these great little cars. I guess the flex of the rim and the compression of the tire create some room for roll but it would be marginal. The point about the pivot being the roll centre in hind sight is obvious but I never though of it in that way. I now understand why the freedom of movement is so important, guess its time for a rebuild :)

Marc

I'll post some pictures by tonight. We did the development on Cmunro's car. I really like how it drives. It is very forgiving and incredibly smooth.

To follow on with this and a post of yours quoted further up the page from a different thread.

In a static mode the pod weight distribution will affect the weight on each tyre, broken down to it's simplest form the pod by itself is a simply supported beam (the tyres being the supports), now assuming for a moment the motor is the only thing that has any weight.
If you put the motor directly over one tyre then that tyre has 100% of the load.
Put in the centre each tyre gets 50% of the load.
1/4 of the way across, one gets 75% the other gets 25%.

Could you please clarify the last sentence?

Are you saying you leave the plastic pivot housing that bolts to the chassis slightly loose so it can move about slightly?

here are the pictures of Charlie's Car:

https://reflexracing.3dcartstores.co...nsverse_01.jpg
https://reflexracing.3dcartstores.co...nsverse_02.jpg
https://reflexracing.3dcartstores.co...nsverse_03.jpg
https://reflexracing.3dcartstores.co...nsverse_04.jpg

Since the rear pod runs on a solid axle and has no suspension.

One could say that:

A - The rear pod influences on the main chassis' handling is marginal? It only contributes to forward and aft weight transfer to the main chassis via the central damper?

B - The main chassis is the main component where the majority of the suspension is at work. Front springs, central damper, and side springs.

So really, when it comes to tuning a 1/12th, we are finding a balance between the front and rear end of the main chassis?

Sorry, it all sounds silly, but I'm just trying to express my ideas to further understand this class. :)

I'm shopping for a 17.5 to run with 1s on asphalt. What do you guys recommend?

Double post, see below.

I'm in the final stages of assembling a RC12R5.2 kit and I hit a little snag. Using a Futaba S9650 servo and a small Kimgrough servo saver, one of the ballcups attached to the back of the saver hits the servo when the wheels are turned to the left. If I adjust the ballcup to be perfectly vertical it clears the servo, but if it twists a bit the edge of it hits the servo case.

Is there a good fix or trick for this?

Assuming I understand your explanation correctly, I would just recommend setting your steering throw so that the endpoint is just before the ballcup hits the servo case. You should still have plenty of steering throw.

(This is what I have done on every one of my 12th scales...)

I don't agree with this statement. The next time you have some practice time, try placing some lead weights on your lower pod plate (not much, even 7g will make a difference.) You should notice a pretty big difference in how the car feels.

My take on this whole thing is that because the pod is unsuspended, it is an especially vital part of the car to get right. Weight and CG of the pod both contribute immensely to making sure the car doesn't hike and the rear stays flat when cornering.

The length of the pod (distance from pivot to rear axle) will have a huge impact on how the car feels. Hell, even just changing rear ride height, and thus changing the point of mesh between the spur and the pinion, has a huge impact on car feel.

EDIT: My usage of the term 'huge' is debatable, so feel free to insert whatever term you might prefer. I would recommend trying it first, though, before claiming it doesn't have much of an effect ;)