29.01.2022 Category: Site news
Episode 4: Tires - ‘round and black ones’ is not good enough for a racing sim…
I remember Ronnie Ton was once asked at a race what tires he was using, he said: ‘round and black ones’. Typical Ronnie. A vast underestimation of the importance and complexity of tires.
In the automotive industry it has taken many years to come up with accurate tire model physics, and this process has surely been accelerated by developments in Formula 1. Tires play such an important role in F1 and in fact all classes of racing. Sim tests have become a critical part of the preparation of F1 teams for a particular track, before an F1 race, and even during a race weekend. The physics models used for F1 are probably developed in close collaboration with tire manufacturer Pirelli and I would not be amazed if all teams use the same tire physics.
But what’s the situation in r/c? R/C tire manufacturers don’t have the means nor the knowledge to set up a serious tire testing development program. In r/c it is very much development by ‘trial and error’. You try a certain rubber compound, test it on a track, take lap times, ask the driver how it ‘feels’: very practical ‘trial and error’ development.
But to develop an r/c racing sim you need to somehow create a physics model that describes very precisely how the tire will work under all circumstances. And it is widely understood by tire experts that with tires nothing is linear, meaning that when you double the load the actual traction forces don’t double but moves along a certain curve, to give just 1 simple example. And these curves determine how the car feels.
Why are tires so complex? There are so many variables:
- Rubber compound
- Grip factor
- Surface structures
- Temperature effects
- Drive forces
- Deformation of the contact surface
- Deformation of side wall (not so much with foam tires)
- Tire wear factor
- Camber angle (changing the contact path)
- Toe-in and -out changes
- Steering angle
- Caster angle changes
There are probably a lot more. I am not an expert in this field, by no means, but this is what I learned from our physics wizard Todd ‘Doc’ Wasson while he was developing the tire physics. It all started with foam tires because that is what was used on 1:8 and 1:10 nitro cars which we developed for VRC v3. Todd made it clear that each type of tire would need its own tire model parameters, rubber tires for 1:10 electric, and rubber tires for off-road cars.
Todd had already some good understanding of tire physics models, but what data to work with, to compare with? We had datalogger data with acceleration curves and cornering speed with different tire compounds from which we could calculate some basic grip data. But as already explained earlier, tires don’t work in a linear way. The only way to find out was to set up a tire testing project. And here yet is another mysterious ‘coincidence’ in our quest to develop realistic physics for VRC v3...
Todd lives in Minneapolis, Minnesota, just a big city, one of thousands in the US, in one of 50 states in the US, right? Before he came to work on the VRC project Todd had already established some contacts with a certain Doug Milleken who is considered to be one of the founders of the science of Vehicle dynamics, a real authority in this field. I believe Doug lived somewhere in the middle of the US and had decide to move to… right: Minnesota. Todd contacted Doug about the VRC project and that he was about to setup a tire testing project to obtain data of these little foam tires for model r/c cars. Doug had probably never seen an r/c car before but apparently was interested in the project. Todd and Doug met and had long discussions on how to approach the testing project. In fact, it came down to building a miniature version of a real tire testing rig or machine as used for full scale tires. The principles are of course very much the same: measure the longitudinal (forward) and lateral (side wards) forces under many different wheel and steering angles, tire loads and tire speeds. This is easier said than done. Todd designed the test rig, we engineered and manufactured it, and Todd added the load sensors to measure these forces and wrote the software to capture and analyze the data. The longitudinal measurements were dropped as it was too complex to measure accurately. Because foam tires are so small and relative ridged Todd had to cope with issues like jitter which he had to filter out of the data.
We sent loads of different foam tires, compounds, shore hardness, diameters, front tires and rears, and in a later stage 1:10 electric rubber tires. Todd and Doug did numerous tests and finetuned the testing rig to finally produce the data needed to start modeling the tires. Without this data it would not have been possible to make the virtual cars behave like real cars. All the forces between the track surface and car go through the tires. These forces affect the suspension, roll, pitch, jaw, the chassis movement), the shock absorbers and anti-roll or sway bars resist the chassis movements, transfer forces from one side to the other, from front to rear and back. Vehicle dynamics at work!
I owe Todd and Doug Milliken my gratitude for doing this essential research on the tires. Without it VRC would never have become such a realistic r/c racing sim. How realistic? It can and will never be 100%, it is after all a simulation of reality, and reality is extremely complex as we all know. But we have come close with VRC, damn close!
Feel...
In the next episode I will zoom in a bit more on the actual tires physics model Todd created, what sort of variables (parameters) we work with. And remember, the sim software must calculate 350 or 500 times (for 1:12) per second the result of all these forces and thus how the car behaves, feels. ‘Feel’ is an essential factor in r/c, strange as you can’t 'feel' anything. It’s the translation of the visual input from the screen into your brain that creates the feel, it is what you expect to happen just like what you expect from a real r/c car. For Todd this meant a totally new challenge, he had never seen or driven a 1:8 nitro car before, talking about ‘feel’…
Tire physics and developing ‘feel’ is next.
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Jose M MModerator
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Ronnie showed a great sense of humor with his answer about tires.
Yes, Pieter, feeling is essential to be a top rider, although some riders feel, but they don't know how to explain it properly.
That feeling, accompanied by a lot of talent, makes a pilot one of the chosen few.
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