Equations of motion for a rotational system

[theone]

Homework Statement

http://postimg.org/image/9fw7awqov/
The question is to write the Laplace transformed equations of motion for the system

Homework Equations

The Attempt at a Solution

I am confused about a couple of things: why is an angle is not defined for the rotation of J2. Does it means J2 does not have linearly independent motion?And the fourth equation of motion (for the second J=0), I can understand the theta 4 term being due to the torques associated with it's motion but I don't get the other term.

 

[OldEngr63]

I think I would suggest that you start by ignoring the thetas as defined, and simply define absolute rotations, phi1, phi2, etc. for each body. Then write the equations of motion. At that point, you will be in a better position to back into the equations you gave previously in terms of theta1, theta2, etc.