How to fix an issue with chain changing size within animation?

Hello everyone,

I am new to BA and hopefully not making any stupid mistakes here, since this is my first post. If you find errors in my manners etc. pls tell me and I will act as I am supposed to.
To the point…
I have been trying to set up a single rubber chain animation rolling around two gears. You can find my work in

Tried to get to the solution using several methods of setting things up, currently using the parent-child option, where the chain is a child to the curve it is supposed to follow. The chain has also a curve modifier on it in order to make the chain follow the curve. Animation runs, but the chain acts weird, since it changes size between keyframes, even though I have not changed the size in between saving the keyframes (start and ending keyframes only), and the chain somehow flips the inner section of itself to outer section in midst of the animation.

Here are two screenshots of the problem, start of the animation first and the ending second:

What am I doing wrong? Is there a single tick, which I cannot find or what is this ‘noob to Blender, writer of this thread’ not finding? :wink:


If you have any ideas, good or bad, I am more than happy to hear them :slight_smile:

Chain_rollin_finally_maybe_2Fix.blend (3.78 MB)You have a great beginning and a good understanding of how to get this done. You are being tripped up by only a couple of gotcha issues.

First, when creating anything, try as much as possible to keep the origin at a control point (i.e., center of object or desired corner). The origins of your rubber chain and curve are high above.

Second is an error in parenting. Creating a curve modifier for the rubber chain already creates a dependency between the chain and the curve. Also parenting the chain to the curve is a mistake. I do recommend creating an empty and parenting everything to the empty so you can move/copy your finished rig to wherever you like.

Attached is your blend file with the fixes:

  1. Remove belt parenting to curve
  2. Re-establish curve modifier on belt
  3. Re-position belt to fit correctly on curve
    (the objects should really be created with origins at center of geometry)
  4. Create empty and move to center of everything. Parent all to empty
    This allows you to move the whole rig where you want.
  5. Reset driver for x position of belt to -y rotation of gear * 0.46256

Hope this helps shed some light. Keep up the good work.


Brilliant, thank you so much Blurfoot.

Now the chain rolls and I can copy it + move the copy to another location where it rolls just as nicely =)

Note: This thread is now solved. I will mark it solved once I get permission to do that (below 10 msgs still).