Box2D robot arm simulation

Just a little scene to get my feet wet with using keyframes to animate segmented limbs by setting the motor speeds. For now, each keyframe is a separate json file which contains the entire world, but only the 3 angles of the arm are actually used.
This scene was set up in about 3 hours using the R.U.B.E editor.
Code available here:
The control in this video is entirely automatic, which was quite handy because touching the testbed window seems to make XVidCap crash #&"#$&!!!