simtk.org

To whom it may concern,

I add a torque actuator to my model with tibia as a body A and femur as a body B. I am running RRA and then CMC to get torque that has been used by this actuator. I have some questions about this torque expression:
1) What is the reference frame for this TorqueActuator's expressed torque? What I know based on OpenSim API, it is expressed on femur's body coordinate called generalized coordinate of the knee joint. Is this correct or not?

2) To validate my results, I am getting joint moment from RRA and from AnalyzeTool, I am getting the MusclesMoment around the Knee Joint. Then we have: JointMoment [Knee Coordinate] = MusclesMoment[Knee Coordinate] + TorqueActuator_Moment[Knee Coordinate]
and since I have Joint Moment and muscles moment, I can easily derive the actuator's moment:
2.1) when we are extracting the MusclesMoment by Analyzetool, Are the muscle moment expressed on local coordinates like knee joint
coordinates or it is expressed based on global coordinates?

2.2) I was expecting the same TorqueActuator's moment which was derived by CMC directly, However, they have considerable differences.
I could not explain these differences between two torques which were expected to be the same. Could you please give me a
reasonable explanation on this difference?

I am looking forward to hearing from you as soon as possible,
Many thanks,
Ali.

Dear All,
Since it is a little bit urgent for me, I would be very grateful if one of the OpenSim developers or someone who knows the OpenSim in advance can help me or guide to get the answer.
Sincerely,
Ali.

Hi Ali,

Thanks for your message. It seems you are aiming to compare the muscle-generated joint moments + your added torque-actuator-generated moments to the inverse dynamics moments for the same motion. I did something similar for a previous project. There are some scripts here that might be a good starting place for you. Check out the "ModelWithSampleSimulations" download; there is a 'scripts' folder that includes Matlab scripts to load results from a CMC or MuscleAnalysis, compute quantities like those you are interested in, and plot results. The README.pdf can help you navigate the various files.

Cheers,
Apoorva

Hi Apoorva,

In your project, you call functions such as "setMassOfBodiesUsingRRAMassChange", or "setMaxContractionVelocityAllMuscles", but I cannot seem to find where they are defined. Are they available in the "ModelWithSampleSimulations" download ?

Thank you in advance,

Rodrigo Mateus