I have modeled a machine with tank treads. The treads follow a bezier circle. When I animate the bezier curve by moving it along the “x” axis, I run into trouble. The treads follow the shape of the bezier curve and “rotate” around it, but the motion of the treads will randomly change directions at various points in the animation where NO KEYFRAMES are inserted. I have tried changing the direction of the arrows on the bezier curve in edit mode, but run into the same problem when I go back to animate it. I have tried messing with the animation graph, but that did not work eithor. I have even tried deleting all other animation in the scene, to make sure that absolutely no other animation was causing the problem, and even with everything else perfectily stationary, the tracks still go crazy. I went ahead and rendered it to make sure it wasn’t a preview bug, and the tracks appeared the same in the test render as they did in the preview. What I don’t understand why the tracks are moving backward and foward at random both in preview mode and in the render when the arrows on the bezier curve should limit the motion of the treads to eithor clockwise or counter clockwise. Is this a Bug that someone else is experiencing or is it user error on my behalf? Does anybody out there have any ideas on how to fix this problem?
if you have a good enough connection … go here…
and see that guys tank tread tutorial…
IMHO it’s the best tank tread turorial I have seen…
Thanks for your help. I pretty much did everything in the tutorial and am still running into the same problem. When I “scrub” back and foward without adding in any keyframes, the tank treads behave (both before and after I did the tutorial). However, as soon as I add in the keyframes to get the bezier curve (and therefore the tracks) to move from point “a” to point “b” along the positive “x” axis, the treads will move clockwise around the bezier curve for a bit and then randomly between keyframes decide to slow down and move counter-clockwise for a bit. This will happen multiple times between the keyframes. Any more advice?
Try this…
Create an empty Object… Parent everything to the Empty… Use the Empty as your over all “Move” Object… (don’t move the curve)
If that doesn’t work get back to me…
Here’s a guy who used bones to control movement of the track…
Tank Track Rigg
Heres a quick anim of what I think your wanting to do…
http://http://www.youtube.com/watch?v=pCQZ-UufD9I
Here’s the blender file
[ATTACH]166802[/ATTACH]
The quick animation you did is EXACTLY what I am trying to do. I have been working on a different project the past two days and am coming back to this one today. I am about to try what you reccomended and will get back to you on whether it works or not. Thanks again for all your help!
Ffiinnaallllyy!!! It works!! 
thank you so much!!
Okay… well… note that my set up was not quite the same as some of the other videos…
I don’t move the Curv’s cause I because they I can’t use them to rotate when I want my tank to make a turn… so the Box Object… or Tank Hull… is the overall parent to the curves and the TrackLinks… so the Hull does the turns… then I move the Track links to make the tracks move… It’s not as kwell to have to do it that way but it works… so… you just have to look at the animation play back with the Graph Editor open to adjust everything such the tracks don’t look like they are playing ‘slipin slide’ on the ground… doesn’t take too long to adjust… so…
Glad that helped…