Applying External Loads_Squat in ZeroGravity

[Satya Sri Mummidivarapu]

Hello all,
I’m trying to simulate squat in Zero gravity to understand Muscle forces and Joint reactions. I want to apply constant force at the shoulders of the Model during the activity. Since I’m performing simulations in zero gravity, without a constraint my model keeps falling down (while running without ground reaction forces at foot as in 1g) and shooting up (with ground reaction forces as in 1g). I have used two Weld constraints one each between COM of toes and ground.
How can I apply constant force at the shoulders to the model?
I have tried the following, but looks like I’m applying these shoulder forces improperly or they are not getting translated to the lower limbs.
Issue 1: I have tried giving shoulder loads in the External loads.mot file where Fx = Fz= 0 and Fy = -250N and the position is given as rAcr and lAcr positions with respect to ground. Also, while editing the forces in External forces.xml file I have applied force on the torso (forces and points expressed in ground). This method did not help me, using preview of experimental data for external loads.mot file I could see the forces are acting near opensim coordinate axes origin but my model has translated along x axis. Can someone help me identify what I’m missing here?
Issue 2: The results looked similar applying shoulder loads and without applying them which they are not supposed to.
Can I model this constant load in the model using Point Actuator? What would be the difference between using a point actuator and as External Loads? How can I change the control values in Point Actuator code to always output constant load?
Can someone point me to the addition documentation on editing Actuators, Tasks and Control Constraints xml files if there is any? I have been fiddling to edit them unsuccessfully, which points me to the errors like, “Not all degrees of freedom are actuated” or “One of the coordinates are fixed” (which they are not) or something like Unidentified Coordinate
I apologize for the length of the question and any responses in this regard are golden. Thanks a bunch.

Best regards
Satya

[jimmy d]

You can set gravity in the model. Have you set it to zero?

[Satya Sri Mummidivarapu]

yeah! I have set the gravity to 0 with in the model.