[ODE] Brakes and rotational damping

[Matthew Harmon]

>> Yes, there is a problem with simply reducing angular velocity, because
brakes *do* produce "counter-torque". <<

Ahhh... very good point.  It won't make much of a difference in my situation
(very light wheels, very heavy chassis) but that clearly exposes a problem
with the velocity-based system.  Thanks for pointing it out!  I think the
AMotor handles that correctly, but I totally neglected it when I switched to
applying the torques to the wheel myself.

So, to do a brake correctly it must apply a torque both to the wheel AND
equal and opposite to the chassis at the point where the brake would be
connected.  I guess that makes sense.

Thanks again.