Here, I have derived by hand the equations of motion for a rolling disc. The scanned document at the bottom shows the steps I went through.
This is to show what PyDy (my Google Summer of Code 2011 project, under SymPy) will be doing; by using SymPy’s symbolic manipulation abilities, one can use the functions in PyDy to derive equations of motion symbolically. A simple system like the rolling disc can be done by hand easily but for larger, multibody systems you will need some computational assistance.
PyDy is primarily built around Kane’s Method 1 , but will be able to work with Lagrange’s Method or Newton-Euler.
Edit: PDF removed for now until I fix an error….
1. Kane, T. R. and Levinson, D. A. (1985) Dynamics: Theory and Applications. MacGraw-Hill Series in Mechanical Engineering. MacGraw-Hill Book Company, NewYork.