[ODE] Balancing a bike

[James Steele]

I'm in the middle of trying to implement the dynamics required for a 
motorcycle and currently, am working on ways to balance the bike also 
cause it to lean into a turn.

To get a quick and dirty version going, I just applied a fixed torque 
value multiplied by the inner-product between the up-vector of the 
body's rotation and a unit y-vector.  To avoid unwanted oscillations (as 
this was essentially a spring) I dampened the torque by a force 
multiplied by the angular velocity around the body's at-vector.

While this does work, it's rather limited.  What I really need is to 
specify a desired "up-vector"  for the body, and use a  joint motor to 
control the torque required to orient the body correctly. So my question 
is; is there an existing joint in ODE that will allow me to constrain 
ONLY THE ROTATION around one-axis of a single body?

If not, how easy would it be to implement a joint in ODE that does 
this?  Is there anybody who can give me some hints on this? 

thanks in advance!
James