That's a good book indeed. I had lunch with the author once at a convention
Indycars were on my mind since I'm going to the race again this year
This link below is just a quick example of some of the lap times. They do a 4 lap qualifier there and fairly often the first lap is the quickest. They do also run an outlap and a warmup lap prior to deciding whether to go for it or wave off the attempt, so there's a fact that could be used against me
http://www.autoracing1.com/article.asp?id=360
I think you'll find the same thing in Nascar and other series where they only run a couple of laps to qualify, but would have to double check that to be sure. A friend of mine works as a simulation/dynamics guy for Nascar and insists that tire pressure has a whole lot more to do with grip than the core temperature does. They need to be careful not to get too hot, but they aren't shooting for a particular operating temperature necessarily that produces the best grip. Pressure yes, temperature no...
Fair enough. I'll leave that one alone
Last edited by jtw62074, .
Here's a thought to ponder:
If cold tires have less grip than hot ones, why is the very first lap on a qualifying run so frequently the fastest lap those tires will ever do, even in a series where tire warmers are not used? All they do is crank up the tire pressure and off they go immediately with the very fastest possible, albeit ambient temperature, cold tires.
150C is absolutely possible, btw.. Nascar sees core temperatures in excess of that regularly. Surface temps can run a lot hotter in some situations. I was told of an Indycar tire test where a fellow saw 370C momentarily on infrared during an extreme braking test (high slip ratio, but not locked). Quite a bit of smoke though probably
If cold tires have less grip than hot ones, why is the very first lap on a qualifying run so frequently the fastest lap those tires will ever do, even in a series where tire warmers are not used? All they do is crank up the tire pressure and off they go immediately with the very fastest possible, albeit ambient temperature, cold tires.
150C is absolutely possible, btw.. Nascar sees core temperatures in excess of that regularly. Surface temps can run a lot hotter in some situations. I was told of an Indycar tire test where a fellow saw 370C momentarily on infrared during an extreme braking test (high slip ratio, but not locked). Quite a bit of smoke though probably
Good to hear, YoYo and Flyby. I don't have a working wheel at the moment so can't try it out. Does the steering torque drop to nothing around or passed the limit?
I don't have a working wheel at the moment so can't try it out. Does the steering torque drop to nothing around or passed the limit?This is indeed similar to self aligning torque. However, strictly speaking, "self aligning torque" is the torque that exists strictly in the tire's coordinate system around an axis going straight down through the top of the tire to the ground, dead center in the middle of the contact patch.
http://www.performancesimulations.com/files/sat4.JPG
Self aligning torque is illustrated by the left column of pictures. The little red circle is the center of the contact patch (or any point along that line that is sticking out of the screen at you). The lateral force (cornering force) is the red line. At different slip angles the center of force moves around a bit, which is why you get self aligning torque at the tire (as opposed to the steering wheel) that changes with the total force and slip angle. When you see results from a tire force test where (self) "aligning torque" is shown, you are looking essentially at the blue line multiplied by the red line. This is only part of the force feedback picture, however, and many sims miss this entirely (not all sim programmers are vehicle dynamics experts) which is largely why these discussions happen at all
What you're really talking about in your comment above is "steering torque," which is what you feel at the steering wheel. The "self aligning torque" is part of this, but not the entire picture. Generally it's only a small part of it, really. Many sims only seem to pay attention to the "self aligning torque" part. When you drive a sim and find that changing the caster angle has no effect on the "steering torque" (what you feel at the wheel; the actual force feedback), and more importantly, if you find that the steering torque gets stronger to a point and then suddenly drops off to nearly nothing as you get to the cornering force limit, you're most likely looking at a model that is using nothing but the self aligning torque (the part measured only at the tire). rFactor and NetKar seem to be good examples of this. However, to be fair, if the caster angle is 0 this is largely correct.
This isn't all as complicated as it might sound. All you really have in the end is a force at the tire (or you can consider them to be 3 components of the same force: lateral/right/left, longitudinal/forward/backward, and vertical), and a torque arm. When attached to a car, the tire doesn't really steer around the center of the tire contact patch like you see in the left column of the sat4.jpg diagram. Instead, it steers around an invisible axis in space between the upper and lower steering knuckles on the suspension. More programmer art:
http://www.performancesimulati ... m/files/steeringaxis2.JPG
The red lines are (supposed to be
) the upper and lower suspension arms. The black line connecting them is the steering axis. The tire steers around this. In the diagram on the right side, there is a longitudinal (forward or backward) force from the throttle/brakes. This force does indeed cause a "steering torque" since it's offset from that steering axis by some distance. In a RWD car you only get a force here generally when you're using the brakes, so it's not nearly as noticeable as it is in a FWD car. In the above diagram, it's not hard to imagine that if you pushed forward on the back of the tire it would try to steer to the left, and vice versa if you pulled backward on it. This is the same diagram basically, but showing steering axis along with the kingpin and caster angle:
http://www.performancesimulations.com/files/steeringaxis.JPG
In the end, you just have a force at the tire and a distance to that steering axis, basically. This is where the "steering torque" comes from. There is also a bit more modification to this as a result of the steering linkages that connect the tire ultimately to the steering wheel through the tie rods and so on, but it isn't all that necessary to understand that in this discussion so far.
In the sat4.jpg picture, the steering axis is represented by the green circle in the picture on the right. For the sake of this discussion it would be good to draw a third column with the steering axis offset to the left or right some amount too. Then one could see how the forward/rearward forces also contribute to the "steering torque."
Great work, Vinny! Keep it up. Looking forward to seeing more
Interesting. Didn't know that. Thanks for the info.
Oh, right... That 600 was for the tires only when the main engine was at 300 back then. I just checked and currently (I was wrong) the main engine runs at 250Hz with the tires running 500Hz most of the time. At low speed the tires switch to 1000Hz. The RC car tires have almost 0 inertia so you need to run them at a pretty high frequency as you can imagine. The 30,000Hz was overkill. At one point I think I had them running at 60,000Hz. A bit unnecessary
Just like Bob said, it's smoother.
Literally what you're doing in a simulator is calculating the new position, speed, etc., (let's call it the "state") of the car over and over. You can say "the car's speed is now 100 km/h, so where will it be x seconds from now at that speed?"
The "x seconds" is where the frequency comes in. If you calculate the new position/velocity (state) for 1 second from now, the engine is running at 1Hz (cycles per second). That's not very good because nothing you do over the course of an entire second will effect the car at all. The suspension and other forces won't do anything either during that time, so you're better off calculating everything much more often.
In my case on Virtual RC Racing, I say "the car is here now, so let's calculate where it will be 1/250th of a second from now." That's 250Hz. The tire rotational speeds are calculated 2 times during each step, so the frequency there is double: 500Hz.
At some point you don't notice any difference. I can't tell a difference between 250 and 1000 or 10000 Hz in my stuff (I've tried them all), although some people might. Running 1000 versus 250 takes 4 times the processing power though, which means you have that much less available for graphics, sound, AI, etc., so the name of the game is to run as low a frequency as you can get away with while still maintaining good accuracy and response.
Not sure where the 600Hz came from. It was 300Hz originally and somewhere in the middle I changed it to 250Hz in one of the updates around V2 or V3. The 30,000Hz was only very briefly many years ago (well before Virtual RC Racing was ever released; possibly before I even started work on it) and that was only for the tire model.
Anyway, it's 250Hz now with the tire model running at 1000Hz. Nobody ever noticed the change from 300 to 250, btw.. Up until now I was the only person on the planet that knew
Don't get too excited about Runge-Kutta solvers. That doesn't make something work like it's 400Hz instead of 100Hz. Just a bunch of marketing BS really...
360Hz is an odd one along with a couple of the others. You could use any frequency you want of course, but if you follow the practice of using milliseconds for timing things then you'll wind up using a multiple of 1/milliseconds. I.e., 1ms = 1000Hz, 2ms = 500Hz, 3ms = 333Hz, 4ms = 250Hz, 5 ms = 200Hz, etc.. That's not a requirement at all, but that's why you'll frequently see these familiar numbers popping up in different sims whether they're racing, flying, boating, first person shooters, and so on.
I thought I'd read way back on rec.autos.simulators that GPL ran at 333Hz. I could be wrong though of course.
Last edited by jtw62074, .
I always thought it just ran at half the refresh rate. So 60Hz would give you 30fps max. I didn't know there were CRT's that went to 150
I don't have an NDA (I'm not a beta tester or involved in the slightest). Just something I was told by a little birdie. If they ever discuss it publically I'll come back and say what it was
People like this should just be dragged into the street and shot. :bandit:
I expect it to be really good and worth the money for many die hard simmers. They're doing at least one very important thing that no sim developer has done yet and I'm sure it will show..
I'll certainly be running it for awhile at least. Maybe longer
I'll certainly be running it for awhile at least. Maybe longer
3D glasses liquidation sale $10 each
I haven't tried these, but for $10 instead of $100 you can't go wrong. Be careful to read the article. They work only on CRT monitors and need an NVidia card.
http://xforce3d.com/
http://xforce3d.com/
I explained how this works in quite some detail here:
http://www.lfsforum.net/showthread.php?p=539489#post539489
Throw away that graph. It has no bearing on tires. The dynamic friction of tire rubber is higher when it's sliding at some velocity than when it's not
Almost. It does tend to flatten out which may give an impression that it drops just because it stops increasing, but there is some measurable drop in steering torque as the aligning torque drops. It's just not vanishing completely because there is mechanical trail in addition to pneumatic trail per my post.
A FWD under hard power is different from a RWD, though. There are forward/rearward forces involved there that aren't present in the RWD case.
As someone else mentioned, power steering changes the whole game. You can make a power steering system give whatever kind of torque response on the steering wheel you want these days.
As someone else mentioned, power steering changes the whole game. You can make a power steering system give whatever kind of torque response on the steering wheel you want these days.
I don't think there's been a sim in many years that works any other way. Even most of the ones that people call arcade use rigid body dynamics.
I'd like to see it too, but good luck. Not many sim developers discuss those types of details publically.
If that graph is vertical tire load, I'd guess the oscillations are primarily a tire spring effect. If you lower the air pressure a bunch the frequency should get reduced if that is the case.
Interesting. I wasn't aware the thermal sensor bit was being done either, but am not all too surprised. Calspan does this at their tire testing facility. There are three sensors just after the contact patch.
Someone told me about an IR camera that was mounted to an Indycar pointed at one of the tires for testing at the Indianapolis Motor Speedway. I don't know how common that is or when it was done, but he said the videos were very interesting. This wasn't for sorting out the car setup like the sensors you describe are probably for, but rather for the tire engineers to look at.
Granted, the temperatures you see with both of these systems are surface temperatures rather than the pyrometer readings down near the cord, but still a very useful thing to have, especially for the tire compounding guys. I wonder if there are any cheap types with reasonable accuracy to play with on a road car.
Someone told me about an IR camera that was mounted to an Indycar pointed at one of the tires for testing at the Indianapolis Motor Speedway. I don't know how common that is or when it was done, but he said the videos were very interesting. This wasn't for sorting out the car setup like the sensors you describe are probably for, but rather for the tire engineers to look at.
Granted, the temperatures you see with both of these systems are surface temperatures rather than the pyrometer readings down near the cord, but still a very useful thing to have, especially for the tire compounding guys. I wonder if there are any cheap types with reasonable accuracy to play with on a road car.
No. Kart Champions is a different sim. We have nothing to do with it.
Tire deformation - Slip angle test
Hi guys,
Rather than dig up an old thread that might not remain entirely on topic I thought I'd make a new one. For those of you that have never seen a tire test, check this out from the Delft facility:
http://www.youtube.com/watch?v=mrp97ImbKBc&fmt=18
This is one way that engineers come up with the slip angle versus lateral force curves for real tires. Here we see a "drum test," named after the large steel drum the tire is rolling on. Other tests include flat belt tests where there's no curvature; sort of like a giant belt sander with treated steel sheet (a little more accurate), and tests where the tire is towed on a big trailer over a real road surface.
For racing sim developers, this is a great way to get a look at tire deformation in controlled circumstances too
Rather than dig up an old thread that might not remain entirely on topic I thought I'd make a new one. For those of you that have never seen a tire test, check this out from the Delft facility:
http://www.youtube.com/watch?v=mrp97ImbKBc&fmt=18
This is one way that engineers come up with the slip angle versus lateral force curves for real tires. Here we see a "drum test," named after the large steel drum the tire is rolling on. Other tests include flat belt tests where there's no curvature; sort of like a giant belt sander with treated steel sheet (a little more accurate), and tests where the tire is towed on a big trailer over a real road surface.
For racing sim developers, this is a great way to get a look at tire deformation in controlled circumstances too
Proper collision response is really hard to do. I spent the better part of the last year working on a new system for mine, and it's not perfect by any means. I'd rather see the LFS guys doing other things, personally. Good drivers don't crash too often
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