You could contact the owners of that project: https://simtk.org/projects/c3d2opensim
Or you could search the forum to find similar questions and answers: viewtopicPhpbb.php?f=91&t=10025&p=0&start=0&view=

The SpatialTransform in OpenSim describes how the Child frame moves with respect to the Parent frame of a CustomJoint. It specifies the permissible movement (by user provided functions) on 6 axes (3 rotational and 3 translational TransformAxes) parameterized by generalized coordinates (the joint's c...

Consider posting on the CEINMS forum: indexPhpbb.php?group_id=840&pluginname=phpBB

You do not need additional actuators to lock a joint. You either a.) care about the coordinate force necessary to enforce the lock (that is what ID provides now) or b.) you don't, in which case can simply ignore what ID computes. Adding an actuator to enforce the lock (to result in zero residual) wo...

It could be helpful to see the command(s) you entered in the scripting shell. Some guesses are that you may not be providing the complete path to library and/or you a providing the library's file extension.

Adding PrescribedForces seems like the right way to go if you want apply external forces at known points on the model as functions of time. If it is point forces between bodies in the model, then use a variant of a PointToPointForce (Spring, ExpressionBased or Actuator).

A couple of things come time mind: 1. Is it possible that the handle is imparting large moments on the hand that requires very large shoulder internal rotation and forearm pronation moments (e.g. to twist the handle) to oppose it? How is the handle modeled and which "r_z" coordinate was limited and ...

Plugins (MacOSX, WinX64) for 4.0 were just added to the SimTK page for the SacpulothoracicJoint: https://simtk.org/frs/download_confirm. ... oup_id=986

Validating muscles that control the scapulothoracic joint is a work in progress. Which muscles are you interested in?