1. Have you tried putting a breakpoint in your muscle model function? What are the muscle forces coming out?
2. if the muscle code is being executed are you setting the control value on the path actuator to be the muscle model force?

The order of values is in the underlying SimTK::State object should not be depended on. Adding a constraint or another joint will quickly break any assumed order. To reliably access state values use the services provided by the Component interface. For example: /** * Get all values of the state vari...

Bill, you might want to verify that that the muscle moment-arms of the Arnold 2010 model are valid (at least reasonable) over the complete range of motion you are studying. For example, Edith Arnold herself (http://jeb.biologists.org/content/216/11/2150.full.html) had to adjust the muscle paths of m...

If you are looking at the motion by changing the crank coordinate in the GUI, then it is doing a an assembly at every change in the crank coordinate. An assembly tries to satisfy the current value of the coordinates and your constraints. If there are coordinates you don't care about (you want them t...

A few thoughts: 1) Can the mechanism be assembled to the accuracy specified? It isn't the case that the solution is just out of reach for any value of q considering the precision of the segment lengths? 2) If you know the solution is reachable, what are the initial conditions? Would the violation ha...

You need to get the set of actuators to access yours. You also need to cast to the right actuator type, since you get list of actuators and only you know it is a PathActuator. E.g.: shouldBePathAct = model.getActuators().get('pathAct_LK''); pathAct = PathActuator.safeDownCast(shouldBePathAct); VMT= ...

Why introduce the pedals if you don't want any dof there in the first place? If the foot is effectively welded to the crank are you really expecting the foot to rotate 360 degs and more as the crank goes round? What exactly are you trying to model? If the foot is going around fixed w.r.t. the crank ...

I am currently using LKnee_rz as the position, and LKnee_rz_u as velocity. Is that correct? That does not sound right, unless you are somehow using the change in knee angle to compute muscle length in your code? If your MATLAB muscle code requires muscle length and velocity then you could ask the p...

You need to model the crank and the pedals. A pin joint can be the center of your crank body. Then you could have pedal bodies that are also connected to the crank with pin joints and then weld the feet to the pedals, or you could use point constraints to connect the feet to the crank bodies at a po...

OpenSim requires adequate number of Coordinates be specified with the corresponding Joint type. In your first use of the FreeJoint with the ground had 6 Coordinates specified and the others have none.
I suspect that is the problem.