Re: Pod balance:

As already mentioned, the rear pod imbalance has a dynamic effect only. It is possible (within reasonable limits) to correct the imbalance with a combination of component/weight placement on the main chassis and tweak screw adjustments for STATIC corner weights on a tweak board or scales. But when the pod encounters a bump, the greater inertia of the heavy side of the pod will put more instantaneous pressure on the tire on that side. Since the imbalance is usually small, and our tracks are usually very smooth, then the effect can usually be ignored.

There are some racers that still run cars with rear pods designed for brushed motors, but using heavier brushless motors, and do quite well with them.

Hey guys and gals. Can somebody please help answer a couple questions for me? 1) what is the advantage or disadvantage to running the battery inline on the chassis and electronics inline (like onpoint) compared to the battery being ran across the back (transverse?) 2) What is the ideal front to rear weight ratio you would want with 17.5 stock racing?

Thanks!

ihmo
I would not recommend balancing chassis electronics with the rear pod connected, unless the rear pod is also balanced, which could be seen as pushing the ball up-hill to no benefit

Weight on the pod is spread across a solid axle, weight on the chassis is not

Any imbalance of the rear pod will further skew chassis balance, if one were to corner weight the car as a whole, or on balance pins

I've given up on pod balance, now preferring to just have the least weight on the pod as possible
Choose the tires your club mates run to start
Yokomo-3Racing offer a nice portable truer at a fair price

I think In-Line vs: Transverse is a tuning option
There is no one way that may work best everywhere, on every car

In-line for more mass centralization
Transverse can have more rear weight bias

Most 1/12 cars are around 60/40 bias

With my SpeedMerchants, Transverse is very good on lower grip, tight club tracks, but Inline was much easier to drive on a super high-grip flowing track like at iic

The rev8 is built for all lipo positions

Here's the Slapmaster take on pod balance:

I use an old Delta tweak board and balance pins. Both of these check the car as a "whole". So if the motor weight is one side or the other in the pod whether it be by design or by motor manufacturer, you will have a natural tendency to correct it by the tweak screws. It's easy to see. Tweak the car with the rear axle on the tweak bar side, front tires on the stationary side. Now rotate the car around putting the rear tires on the stationary side, tap it out, see where your bubble is. If its "on", you are good. If it's "off", something is out of balance in the car.

If it's off, I start by taking the motor pod off with the motor in it. I find some scrap of wire and solder on to best represent what was there if the car was whole. You have to make some assumption to what is a proper amount at the motor and what would be part of the chassis. Pinion on. Just like it was ready to run. Put that on your balance pins and see what that looks like. Different motors have their stators in different locations in the can which is really difficult to balance. I have machined up spacers that go with each motor manufacture just to get it right.

Of course, check your chassis (minus the motor pod) in the same way. Shift your electronics until it's balanced.

Now reassemble your car as if its ready to run, put it back on the tweak board. If you are blown away by how far off your tweak screws are, you will be more excited to hit the track!

By correcting this, what I would feel is how the car would handle chicanes and similar driving arcs. With an imbalanced pod, I would see a wgt car lift an inside wheel which of course is wheel spin. I have had 12th scales turn slightly better one way vs the other when it bubbles out. Balance it, whoa!, runs the same both ways. You can spend hours fixing this, but it's worth every minute.

I have also seen guys rest their chassis about 50% perpendicular off the edge of a set up board, front tires off. Put just a little pressure on the front until the rear tires come off and then visually look to see if the gap between the board the rear tires are the same. It's a quick and dirty way to check for tweak and balance. BTW: I feel this only works if your front end springs and downstops are all correct.

Brian

I was curious about the new Rev.8 and went to the SpeedMerchant site...I found this pic of Josh Cyrul's Rev.8 with a mysterious black box in front of his ESC:

What is that thing?

Looks like a receiver battery

The Rx pack is behind his esc, the box in front of his ESC is a fan. He said he needed the fan due to the heat on his mod car.

Isn't that behind his ESC?

Sorry, I think it is a fan (kave beat me to it)

A fan is always a good idea for mod, especially where you have 160+ track temps

The rev8 mod 1/12, with Josh at the wheel was turning laps nearly 2s faster than Mod TC at the Nats

Wow, ran, and won, on a surface hot enough to cook a steak on and didn't even puff the battery. That is impressive.

Speculation by an expert is sometimes all you need. Theory is fine, but it doesn't always work in practice!

The issue with a 12th car is that it is a racing chassis with a hinge in the middle. Much of one's perceived wisdom about weight distribution therefore goes out of the window.

RedBull - thanks firstly for finding Mike's original post. After ten frustrating minutes I couldn't! Thanks secondly for pointing out the key difference between balancing the front and rear of the car, and how it should (not!) be done.

Each end of the car is sitting on three points. At the rear, those three points are solidly connected through the axle and the bottom pod plate. Generally speaking, all the weight inside those three points (the two tyres and the centre pivot) will even out over the there points giving an even weight distribution across all three. the comments about dynamic imbalance still apply, but balancing the car is a static event, not a dynamic one.

The situation with the main chassis is different. The three points are disconnected because the front tyres are sitting on two springs independently pivoted from the main chassis. The weight in the chassis will unevenly distribute itself across the front tyres because each can accommodate a different weight as it pivots independently from the main chassis.

If you take the pod off the car and balance the main chassis with all its elements fitted you will evenly distribute its load across the front axle. Ignore the rear pod - within the limits of the different motors' weight distribution the weight will be pretty much even across the rear tyres.

Now reconnect the chassis to the pod and set it up on the tweak screws using whatever method takes your fancy - tweak station or coin-drop test. If you do that and then put it on the corner-weight balances, you will find it is within a couple of percent from side to side on the front wheels. That's what I do and I get within 1% most of the time.

For this to be accurate you need tyre sizes exactly the same on each side of each axle. As they never are, there is always some imbalance. You don't stop halfway through a race to swop your tyres over, so don't sweat the chassis balance too much on the bench. HTH

Hi
Couple of questions.
How do you calculate the roll centre of the rear pod?
How does the centre of gravity of the rear pod affect the roll if it is off centre?
Is the system really connected by a pivot, this sounds silly but if the the side springs are sufficiently compressed i would say its no longer a freely moving pivot.
Interested in your views.
Marc

Can 1/12 pan car perform on concrete ?