XRAY - Model racing cars

When you [Tony] talk about flex I'm assuming you are referring to a torsional displacement [twisting] of the chassis.

There are a couple of points I would like to pick up on:

1) You mentioned that designing in flex is important. OK, so as we do with springs we have a range of options for controlling the torsional stiffness of the chassis but what is the sequence from least to most compliant chassis. As far as I can tell there are 4 variables, lower chassis, upper deck, with[out] front posts and with[out] rear posts.

2) You mentioned that there is not a linear relationship ... what are the traits of the car when you are either side of the sweet spot. It is good that a performance increase can be found by experimenting with different settings but how do you know you are headed in the right direction as there is often a trade off between a setting that is quick but difficult to be consistent with and vice-versa. What I'm really asking is what do feel is different through the sticks (wheel/trigger).

I guess the other point to ask is what sort of priority is given to this variable? Do the team drivers decide on a chassis before tyres/diff/springs/dampers or work the other way and use it as fine tuning option?

Coming from a 1:1 racing background I can tell you this. A stiff chassis with a "perfect" set up will be faster than any thinner flexible chassis with it's "perfect" set up. The problem is that we hardly ever have a "perfect" set up under any of our cars. A more flexible chassis will be more forgiving so you have more room for error with your set ups. For most of us it will be a welcome addition to our cars. Just wish I could get one, still waiting for stores to get them.

TeamGP:
Yes we did this many times over the past few years and again with the FK05.

Like polesitter61 indicates theoretically a stiffer chassis should work better, but this is like saying that theoretically less chassis roll will mean more grip. Both true and both essentially useless statements when we look at the dynamics involved in real life.

On the track less chassis roll means more grip, but that doesn't give you anything if the additional grip is insufficient to cope with the additional force put on the tires during cornering. If the additional grip is insufficient the car will slide out. So you change to softer springs, softer damping, more droop or change a host of other setup options to dampen the force put on the tire at the expense of some of the grip the tyre will give. Result, less theoretical (!) corner speed, but better laptimes overall.

A similar argument goes for chassis flex. Theoretically stiff is better. But who cares if you are sliding of the track loosing many seconds each time?

Polesitter61:
While 1:1 setup theories in general apply, we allways need to take into account a couple of important facts. For one thing the track surface is not to scale. We race on the same asphalt the 1:1 cars race on, except our cars are ten times smaller. I.e. bumps, cracks etc have a ten times bigger effect on our cars than on their 1:1 counterparts. Also, on many corners we have corner speeds in excess of 30kph (tight corners) up to 50kph or more (fast corners). I have yet to see 1:1 cars drive through tight corners at 300kph and faster corners at 500kph (ok, Indy cars may come close).

Screswel:
1) Not sure I understand what you are asking here. If you mean what has the biggest effect on torsional stiffness I am not sure I have a clear answer. I'll try anyway. Generally the chassis is the bigger change if only because it takes a lot of time to make the change. So which chassis you run is one of the first choices you need to make. With the chassis change you change torsional flex at both the front and the back. Next comes the top deck. Using the front-posts you can reduce chassis flex at the front of the car and similarly the rear posts have the most effect on the rear of the car. Both we generally use more as fine tuning options, BUT the actual effect can still be fairly large on the car's handling.

2) This is difficult as there are a lot of variables involved. The answer is that it depends. Both if you have too little flex and too much flex you can have a car that feels like it has too little grip. With too much flex this is often augmented by an unstable and especially unresponsive feel to the car while with too little flex the car will feel great until it suddenly breaks traction either at the front, the rear or both. Be carefull though as there are multiple things you can change to get the car to work better that influence the same basic paramenters on the car.

As to the priorities, they are mostly the result of practicality. The choice for a chassis comes first. Once this choice is made you can optimize the setup for that chassis. Next comes tires and tire treatment as these have the biggest influence on grip. After that comes springs and damping.

Hi

i have just got the 2mm chassis

but have a small problem with it

the plastic cap that the steering bearing sits in, now sits below the chassis by 0.5 mm. Did you team drivers have this problem when testing. Will it affect it at all

thanks

chipmunk

Tony V: I understand what you are saying about the track surface, at our local asphalt 1:1 1/4 mile track the 500lb go carts actually get through the corners faster than our fastest 2800lb cars, and they do it with 10in less rubber on the track than we do!

When i ran mine for the first time, to be fair it didnt feel much different, but as i got used to it and tweaked the setup i found the car more stable at high speed, had better traction and i lowered my laptime on a known layout at my local track.

The battery strap will make the car a little more rigid but however I think the biggest problem with the strap is that it will hold a tweak when you hit things. So either way you will get some handling differences with the strap.

I have been using the straping tape and haven't had problems with bending the battieries. You must make sure that they fit all the way in the chassis. And also that they are strapped in tight. I sometimes will double strap them as well just in case of a first corner crash.

One other thing that you can do is use shoe glue in between the cells when you put the packs together. This glue is like rubber when it dries and will hold the cells together and not allow them to bend.
Hope that helps.
KT