Question

On problem 3 part b should the instantaneous body velocity be a 4x1 matrix. But when I do the work it is still a 4x4 matrix?

Answer 1

To get the instantaneous body velocity you multiply the body Jacobean (6x5) by the joint velocity vector (5x1). That would give you a 6x1.

Answer 2

Is there an easy way to go from body velocity to spatial velocity?

Answer 3

Yes just take the adjoint of the body velocity with ge.