Gravity Test Failure in Released-from-Ground Model (MoBL-ARMS)

[Johnathan Ford]

Gravity simulations failed in the MoBL-ARMS upper extremity arm model in the "released from ground" variations for both 3.3 and 4.1. However, the gravity tests for the "fixed to ground" variations ran successfully.

The attached models are ready for simulation (no modifications necessary), but the testing steps are included below for your information. The only change needed is to update the simulation time in OpenSim 3.3 to 5.0 seconds since it is not the default.

GRAVITY TEST STEPS

Verify that all muscles and other forces are disabled.

Verify that all coordinates are locked except for "shoulder_elv". Note that the "released from ground" version contains six additional coordinates (3 translation, 3 rotation) for the torso, which also must be locked.

Verify that "shoulder_elv" is set to 60 degrees.

Set simulation time to 5.0 seconds, then click "Simulate".

In the "fixed to ground" models, the simulation time should be nearly instantaneous (slightly longer for 4.1 than 3.3). However, the simulation is expected to fail for the "released from ground" models. The simulation will either run very slowly with inaccurate motion or remain stuck at 0.0%.