Inverse Muscular Dynamics

Kris Hauser
December 2001
CS 294-c Final Project

Abstract:
While dynamics uses forces to create an animation, inverse dynamics uses an animation to attempt to find the forces behind the motion. In this project, inverse dynamics is used to try to find the muscular forces that a character would have to exert in order to perform a motion. Such data could be used to drive muscle and skin deformation for realistic characters. My method works for small systems, but things go awry on complicated (e.g. human) ones.

Details:
A powerpoint presentation, detailing the methods used: invdyn.ppt (Powerpoint, 52 kb).

Examples:
If you have a Windows computer, you can download the executable and some test files here (zip, 348 kb). Run a playXXXX.bat file, and press 'z' to start/stop the animation. Dragging with the left mouse button rotates, the middle button zooms, and the right button translates. 'f' toggles showing the joint/collision forces. The red lines are muscles. They get thicker as they pull harder, and when they are inactive, they are in dark red.

If not, you can watch some movies of those test files.

Simple test. Simulating an arm/bicep/tricep.
Springy. Another simple test.
Bounce. Solving collision forces.
2 Support. Two-legged support, with only a few muscles.
2 Support 2. The same, but with opposing muscles. Notice how the results get more odd.
Box Carry. Another failure. This is an ill-conditioned system.
Pushup. A pushup, with many torso muscles.
Pushup 2. The same, with the ground. Somehow, the results seem worse.
Balance. A test of supporting muscles in a complex torso/lower body model. The results don't seem correct.
Squat. The same model as above, performing a sort of squat.
Kick. The same model as above, performing a kick.

Contact:
Questions? Comments? Suggestions? Contact me at hauser@uclink.berkeley.edu.