[ODE] Wheels flipping about perpendicular

[Timothy J. Wood]

   In my car, I had previously omitted code that set the desired value 
for the steering axis.  Without this, when I switch directions on my 
torque, my wheels flip about the Z axis (X is the drive axis and Y is 
the steering axis).  Adding the code to simply specify that I want a 
zero angle about the steering axis stops this flipping, but I'm curious 
as to why this is happening anyway -- shouldn't the hinge-2 constrain 
the axis?

   I suppose that the flip on the Z axis could be just a composite of a 
rotation on the X and Y axis, but only if the drive axis was relative to 
body 1 (the chassis)  instead of body 2 (the wheel) ... or am I 
misunderstanding?

   Not too important since adding the steering axis parameters eliminates 
the flip, but I'd still like to understand why it was failing before.

-tim