Re: RE: Problem attaching motion path in MAYA

Sorry, it's very difficult to offer suggestions in a case like this because we have no idea how that script works or what your hierarchy is like. For example, the script might be tracking the wheels' world position, or it might be reading their translate values directly. Those two behaviours will work completely differently depending on whether or not the wheels are part of a hierarchy, constrained to something else, etc.

Starting from scratch, I would try this:

1. Assemble your tractor hierarchy. This means do all your parenting FIRST. No expressions, motion paths, or animation.
2. Make sure you have an extra transform above each wheel. You can do this just by grouping each wheel to itself.
3. Put another empty transform above the entire tractor (i.e. above the top node in its hierarchy).
4. Attach this new transform to the motion path, using whatever settings you want. This should bring the tractor around on the path while still leaving you the freedom to animate the tractor (and the wheels themselves) separately.
5. Now apply your script to the wheels. Depending on what the script actually does, as I mentioned above, this may or may not work. But if it doesn't work you should be free to try other scripts or just keyframe the wheels by hand.

The thing to remember is that attributes can only be controlled by one input at a time. That means if something is controlled by a motion path, it can't also be controlled by an expression, for example, or if something is controlled by a constraint, it can't also be controlled by keyframes. However, hierarchies allow child nodes to inherit the transformation of their parents, so you use extra transforms to have multiple levels of control over an object.

The classic example of this is a hovering droid that flies along a motion path, while still being free to bob up and down and rotate as it goes. In that case you create a transform above the droid's top node, and attach that transform to the path--this will create the smooth flight. But it also leaves free the droid's original top node, which you can animate with keyframes or expressions to create the bobbing motion. The two patterns of motion will be layered together to produce the final animation.

Hope that helps!