Example: CMC arm26

[Maurice Lang]

Hi everyone ,
I'm trying to better understand the CMC tool so after read about it on the User's guide I've done the example- CMC
but I don't find the "arm26_ComputedMuscleControl_ControlConstraints.xml" file :
I understand that this file must contain something about muscles and actuators, but I don't know how to create it, which data must contain etc, the correct sintax, etc....
so I've run the simulation without it.

Then I've Created a New Desired Kinematics ( IK.mot) file with reserve actuator and Tracking Tasks as in the example,
without the file aboutControlConstraints but the simulation failed:

"CMC.computeControls: t = 0.18
CMC::computeControls WARNING- small force range for TRIlong (0 to 0)

CMC::computeControls WARNING- small force range for TRIlat (0 to 0)

CMC::computeControls WARNING- small force range for TRImed (0 to 0)

CMC::computeControls WARNING- small force range for BIClong (0 to 0)

CMC::computeControls WARNING- small force range for BICshort (0 to 0)

CMC::computeControls WARNING- small force range for BRA (0 to 0) "

This message appears from 0.18s until the end and the arm disappear.

Should someone help me to understand the controlConstraints file and my error?
I also load my .mot file .

Thanks

Maurice

[Thomas Uchida]

The control constraints file is described on the "Getting Started with CMC" page in the Confluence documentation (https://simtk-confluence.stanford.edu/d ... d+with+CMC; search for "control constraints"). I suggest looking at other examples that use CMC, such as "The Strength of Simulation: Estimating Leg Muscle Forces in Stance and Swing" (https://simtk-confluence.stanford.edu/d ... +and+Swing).

[Maurice Lang]

Thank you Tom for your reply,
I've read the links you show me and they were very useful.

The only thing is that I don't unserstand if in the ControlConstrain file is enough to write the
<default_min> and <default_max> for my muscles or if I have to insert also the <ControlLinearNode> that descrives to excitation curve.
Because I don't know the excitation curve for the muscles and only with the <default_min> and <default_max> my problem persists.

Thanks, Maurice

[Thomas Uchida]

You don't need to know the exact excitation curve; you can use a ControlConstraints file to specify the bounds over time. I suggest looking at an example from another simulation (e.g., see Sam Hamner's running simulations, available here: https://simtk.org/projects/nmbl_running/).