Physics: Rotating in place (not in a good way)

I've got the basics of my engine in and every thing seems happy except (and this is a big except) if steering inputs are applied while the car is stopped, it rotates in place (more or less around its own center). Once the car has some speed, this behaviour seems to go away (but steering inputs seem VERY sluggish, especially at high speeds where it is almost impossible to turn...could these problems be related)? I realise that this is pretty vague, but can anyone point me in the right direction? Aaron

Aaron Liebling wrote:

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> > I've got the basics of my engine in and every thing seems happy except > (and this is a big except) if steering inputs are applied while the > car is stopped, it rotates in place (more or less around its own > center). > > Once the car has some speed, this behaviour seems to go away (but > steering inputs seem VERY sluggish, especially at high speeds where it > is almost impossible to turn...could these problems be related)? > > I realise that this is pretty vague, but can anyone point me in the > right direction? > > Aaron

Without knowing what forces you have simulated it would be hard to suggest where to look. If you have a kinematic simulation (modeling the trajectory) then the vehicle should "turn" slower at higher speeds, if by turning you mean the rate of rotation of the velocity assuming you have implemented limits on lateral acceleration. (With the same lateral acceleration, the turning rate will be 2 times lower when twice as fast.) - Matt

On Tue, 20 Aug 2002 04:08:53 GMT, "Matthew V. Jessick" <[email hidden]> wrote:

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>Aaron Liebling wrote: >> >> I've got the basics of my engine in and every thing seems happy except >> (and this is a big except) if steering inputs are applied while the >> car is stopped, it rotates in place (more or less around its own >> center). >> >> Once the car has some speed, this behaviour seems to go away (but >> steering inputs seem VERY sluggish, especially at high speeds where it >> is almost impossible to turn...could these problems be related)? >> >> I realise that this is pretty vague, but can anyone point me in the >> right direction? >> >> Aaron > >Without knowing what forces you have simulated it would be >hard to suggest where to look.

And how, indeed. If you're using forces at all check why it's generating lateral forces. You might use slip angles, which become non-zero when you rotate the steering wheel. In that case, you need to keep the slipangle low at low speeds, or do some other low-speed trick (there are lots and that is a long discussion, but search RAS on 'SAE 950311' on you'll get into the game). Ruud van Gaal Free car sim: http://www.racer.nl/ Pencil art : http://www.marketgraph.nl/gallery/

That looks like the problem. I have some low speed checking to make sure that the slip angle == 0 at very low speeds, but it seems that I'm still getting too much "shaking" in my model when I'm sitting still, so the low speed check always fails. I guess I'll have to try and figure out where the error is coming from and get the car calmed down (at which point the low speed checking should kick in and prevent rotation). To confirm that this was the problem, I bumped up the threshold of what was considered a low speed (and therefore slip angle should be 0) and the rotating in place went away. Aaron Ruud van Gaal <[email hidden]> wrote: : If you're using forces at all check why it's generating lateral : forces. You might use slip angles, which become non-zero when you : rotate the steering wheel. In that case, you need to keep the : slipangle low at low speeds, or do some other low-speed trick (there : are lots and that is a long discussion, but search RAS on 'SAE 950311' : on you'll get into the game).