thirtyfive

I am curious if any "factory" drivers (or anyone else for that matter) would like to comment on the level of development going into your RC cars. It has been a while since I was into RC racing, but from what I gathered during my involvement with the sport, most suspension tuning, motor selection, etc. was based on intuition and rules of thumb as opposed to a deeper level of analysis.

Do RC car engineers use tire models? I would think that the investment to create a tire testing machine that measures lateral force, longitudinal force, aligning torque, slip angle, slip ratio, camber, temps, etc. would be well worth the valuable data that it would produce. In fact, I don't know how you would design a race car (RC or otherwise) without that data.

With good tire data, sufficient kinematic analysis with the car and dynamic analysis with something like ADAMS you should be able to develop your car and tailor your setups for every track surface you encounter. Hell with cars this small even a full K&C rig wouldn't be crazy expensive. So I suppose my question is...do the factory guys do this?

Pardon the long thread.

DS Motorsport

iTrader: (2)

Well i'm not involved in a rc factory, but I do know a couple of things about the subject.

The ''RC Engineers'' do use a very simple tire model, at least the manufacturer I spoken to.
They don't use a program like ADAMS, because it is way too expensive for such a small company.
The thing they will do is some basic calculations with some math models, like rollcentre calculations, camber change, ackerman, caster change.

Currently i'm busy with designing a rc car while making use of the advanced simulation programs like ADAMS, Matlab/Simulink and some other motorsport specific programs.
I have the possibility to do this because the university I study at has all the various licenses for these programs.
I'm currently still testing with a stock Xray NT1 suspension to test the program because it is quite hard to accurately simulate an rc car.
I'm also planning to do some CFD work to test different rear wings and maybe do some underbody aero, trying to create some downforce.
The manufacturer was quite interested in what I am doing, so when I have some results he would like to see them.

It would be cool to have a full rig to test the cars, but for the rig to fully work you will probably need some track data/telemetry. Otherwise you can only do some basic shock testing.
If only AIM or any other would make a miniature data recording set, with shock potentiometers, load cells, ride height measurement.

thirtyfive

Very informative, thank you!

Without tire data I don't know how you would choose your parameters. Obviously your camber curves are going to look a lot different with a rubber tire compared to a foam tire on carpet. And tire load sensitivity is the whole basis for car setup in the first place.

Don't forget about compliance...with these cars there is a lot of it.

Good luck in your endeavor. I've heard of some people using Solidworks in lieu of more tailored software to kinematically model their car. If you find that ADAMS has too steep of a learning curve you may start with kinematic analysis and then move to something more powerful like ADAMS (dynamic, transient, etc.).

timmig

iTrader: (25)

I don't know if they still have it--but I helped design 1/12 scale cars for Roger Curtis and Gene Hustings at Associated in the 80's--Roger built what he called--the "Earthquake machine". It was a table with a steel roller set in at one end--looked a little like a chassis dyno-- the roller was powered to spin with an electric motor--and the roller--was mounted--"off center" by about an 1/8 of an inch. So you could place either the front--or the rear of the car on the roller--and then spin it up to see how the suspension reacted to the "bump"!! It was terrific to tell us which end of the car was working better--it also showed vibration and its effects throughout the car. If the tires were smooth on the roller--you knew the suspension was doing it's job--any car that passed the roller test was definitely smoother to drive on the track!! I put all my designs through this test before they hit the track--it helped a lot for it's simple feedback.
FYI
Tim

thirtyfive

Bump

Chris-s

You can write your own suspension analysis programs in excel, you dont need to spend huge amounts of money on Lotus/Adams/Etc. You can also write your own lap simulator in excel. I'm in the process of doing both, teaches you a lot about vehicle dynamics.

The other part to consider is there is quite a lot of compliance in an RC car, both in stiffness and the fit of components (slop). Not that helpful when trying to model the suspension.

The biggest problem with telemetry is the cost, as miniaturising a data logger wont be easy or cheap, or all the measurement equipment. Unless you were to model certain corners, and just use trailing cables to a labview/data logger setup.

-Rotary potentiometers rather than linear (I've never seen linear ones small enough), use the rotaries and attach an arm attached to the suspension with a drop link.
-You could measure wheel load by adding a link between the shock and tower and adding strain gauges.
-Strain gauge the chassis to measure chassis twist.
-G sensing with the internals of a Wii remote
- Wheel speed would be easy to do, ferrous dots glued to the inside of the wheels, hall effect sensors mounted to the hubs.

ffreitas

I have recently concluded a series of CFD simulations of a Kyosho Mini-Z rear wing.

I posted the results at my blog: haagringnews.blogspot.com