Dear sir,

I would try the function of AnyBody as a multi-body dynamics solver.

Because I’m interested in designing some fitness equipments.

I made a anybody script file which includes the four-bar links. It’s very famous.

Numbers of bodies = 4

Numbers of Joints = 4 revolute Joints + 1 Fixed Joint

Numbers of Drivers = 1

#DOF = 4 X 6 = 24

#CONSTRAINTS = 4 X 5 + 1 X 6 + 1 X 1 = 27

So if I use these joints, this system can be kinematically over-constrained system. Then I could not perform any simulation.

Then, I changed joint construction.

-> 2 revolute joints, 1 cylindrical joint, 1 spherical joint, 1 fixed joint

Then, #CONSTRAINTS = 2 X 5 + 1 X 4 + 3 X 1 + 1 X 6 + 1 X 1 = 24

Then #DOF is same as #CONSTRAINTS, so I could perform the simulation.

I attached twe anyscript files. “WorkingModel.zip” and “RedundantModel.zip”

But in CAD system, even there are four revolute joints in the model, CAD system can perform a kinematic analysis.

I think if there are redundant constraints in model, the jacobian matrix becomes singular, so kinematic analysis can’t be performed. Is it right?

I heard that some dynamic solver like ADAMS, can handle redundant constraints. Its strategy is to modify joint types. But it seems heuristic.

I saw that new version of anybody can handle kinematic over-constrained problems due to motion capture markers. Then, can new version of anybody handle models that are kinematically over-constrained due to joints?

- John Jung