[ODE] Problem with slider joint

[Gib Bogle]

I haven't had much luck in getting responses to any of my ODE questions, 
in fact I've had no luck at all.  In this situation, it's hard to know 
the reason: am I asking a stupid question, is the question ill-posed, is 
it a good question that no-one knows the answer to, is it just of no 
interest to anyone else?  I'd appreciate clarification of this point in 
regard to the last question I posted, which concerned the fluctuation in 
reaction force that I see at a slider joint, compared with using a 
ball-and-socket joint in its place.  In my last tests I've set the Lo 
and Hi parameters of the joint to the same value, i.e. eliminated any 
movement in the joint, but I still see the same variability.  In case it 
appears inappropriate to put a ball-and-socket joint in place of a 
slider, I must point out that in this application (because of the 
geometry) there is no flexing occurring at the joint, the forces being 
in line with the axes of the two connected bodies, and it wouldn't make 
any difference to the motion what kind of joint was being used.

I'd be grateful if a reader who is well versed in all the features of 
ODE could tell me which of the four classes (mentioned above) my query 
falls in.  This would help me to decide what to try next.

Thanks
Gib