Tuesday, August 29, 2017

RC12R6 Chassis Balancing

RC12R6 Chassis Balancing

On the whole, I think people worry too much about this but if you are going to worry about it then do it right:

You cannot/should not balance the chassis as a whole without thinking.

My RC12R6 using latest electronics and a (very light) Muchmore 17.5 Fleta ZX V2 and Hobbywing XR10 Pro 1S is 25 grams underweight (730g is our minimum).

What to do with that weight I need to add?

Rear Pod Errors

Most rear pods are balanced or not balanced based on the motor you are running.

Modified motors are lighter (in general) than spec motors and the latest generations of spec 13.5's or 17.5 or whatever are lighter than the old stuff. If you care, then balance your motor in your pod.

Be aware that you cannot (and should not) correct unbalance in your rear pod buy moving stuff around in the front part of the chassis by ESC and radio gear placement. If you drop your car on the balance pins and try doing the thing as one then you will unkowingly fall into the trap.

When the car is on all 4 wheels on the ground, weight placement in the main chassis has NO effect on the rear pod. Any weight correction is NOT passed through the side springs.

The front main chassis is supported in three places by the front springs via the king pins and the main shock spring via the rear centre pivot. Its a triangle with the single point at the back.

Balance the rear pod on it's own first. 

Here you can see I need 10g of lead strip over opposite to the motor to balance the pod.

So I chop that up and pop it on the back rear corner of the pod under the axle. I glue it directly to the lower pod plate. As low as I can get it without getting in the way of motor movement.

I will need to put 15g somewhere else to bring the car to minimum weight once the balance is done.

Update.... Now, one of our "longest serving" 12th racers in the UK is Fred Hatfield. His critique is this:
I don't think it's a good idea to add weight to the rear pod to balance it because the pod is the unsprung part of the car , better to shim the motor over if you can. Not being critical just a comment .

Well Fred I think is right.... I used to shim the motor over also: I just feel uncomfortable with it in the modern era of the "bottom only" motor screws. And its only 10g... and this motor is already 10g lighter than anything I have seen... and the COG is lower than it would have been with the heavier motor.... and ... I don't like the longer shaft length before pinion that this would cause. All excuses because I do think Fred is right.

Balance the Front

Next I get the isolated front part of the chassis in balance. Our RC12R6 chassis has centre balance pin holes for both the pod and main plate to help with this.

The motor wires are lying in the right place(ish!) and the lose stuff is symmetrical.

The ESC position is tweaked lightly to the left of centre to get the balance. Job done.

Put it all together and check it as a whole (it must be right).

Finally. I cut another 15g of lead and popped it half and half either side of the battery front stop to bring the car to weight.

Small tyres are on. Lightest shell I have (no clips!). I would rather be 5g over than lose a round in tech.

And another sad and final update on this subject!

Kit Associated Clamping Hub
My OCD did not like the stick on weight and I was thinking of other ways to get more weight opposite the diff side.

Then it occurred to me that I had an unused Zen Racing "spider" clamping hub. This is about 4.5g heavier and goes as outboard as you can get so its balance correction is maximised.

I tested the pod balance and with lighter ceramic balls in the diff side it all worked out "good enough". I ditched the stick on weight. OK... its 4.5g of more rotational axle weight but I think its a neater solution.

Would I bother with the Zen piece if I did not have one in stock? .... Nope!

This became one of those things you start that you wish you had not!

Zen Spider Hub

1 comment:

Darren Ford said...

Awesome knowledgeable guy. Great advice thanks again.