Quote - Muralist,

That will work, but that is not the real way that a train wheel set-up behaves. Piston A should be parented to the wheel as well.

If you want the locomotive I rigged to see the set-up, just let me know.

Helgard

Thanks, Helgard, I bought it at www.VanishingPoint.biz a while ago.  I've been digging into it all day.

I've now parented Piston A to the LocoPivotMid (which is in turn parented to LocoWheelMid) and after fixing the joint params its looking good!  All that remains is to get Piston to move now.  I'm rendering a test now; I'll post it in a bit.