[ODE] Brakes and rotational damping

[Graham Fyffe]

ODE does a full solve for contact friction forces in the sense that itwill never introduce backlash.  However, it would be hard to futz thisto get the desired braking effect for a rolling body.  It might bepossible to add a little bit to the "motion" parameter of the contactbased on the direction of spin tangent to the contact, so that thefriction fights both the actual spin as well as some additional"virtual" spin.  Ideally you could add to the ODE code itself to addrolling friction to contacts, to produce the same result without thefeeling of being a hack.  This is even closer to real life in onesense, since the braking is actually introduced at the contact point.But that's going to be tricky.  If you're talking about an arbitraryrotating body, like a ball for example, I would suggest going withyour "sort of" heat bleeding model.  I would only investigate thefriction hijacking method if the heat bleeding method isunsatisfactory.
If you're talking about a car wheel, then you can work the brakinginto the motor joint controlling the wheel.  The simple car demo doesthis within the hinge2 joint used for the wheel motor.
- Graham Fyffe

On 2/8/06, Matthew Harmon <matt at ev-interactive.com> wrote:> Hi all:>> What is a good scheme for applying "brakes" or other damping to a rotating> body?  We've tried a few things but would love some recommendations:>>   - Velocity-Based Damping: Grab the angular velocity, reduce it, and put it> back.  This is easy, avoids "backlash", but probably isn't kosher and I> imagine may result in non-physical behavior in ODE.  However, this is "sort> of" how brakes behave – they simply reduce any existing rotational velocity> bleeding it off into heat.>>   - Add "counter-torque": Apply a torque opposing the current angle of> rotation.  This works, but has the "backlash" problem where applying too> much torque will cause the body to reverse it's spin.  We check for backlash> and "lock" the body if it switches direction… but this feels a little like a> hack.>>   - Add a contact friction joint: This seems to be the most realistic model,> but probably overkill.  Since, I believe, ODE simply adds little forces for> contact joints, it may have a "backlash" effect also.>> Any recommendations or best practices here?>>> _______________________________________________> ODE mailing list> ODE at q12.org> http://q12.org/mailman/listinfo/ode>