Information on how actuator excitation magnitude is related to force, torque

[D T]

Hi,

I would like to know where I can find more information on how muscle or joint actuator activation magnitudes (usually excitation between -1 and 1) can be converted or calculated as force (N) and torque (Nm). More specifically, I am working with SCONE to create an ankle joint actuator that converts parameters given for the gastroc, soleus, and tibia anterior muslces to a direct joint actuator. My question is specific to OpenSim however.

For example, the aforementioned muscles when given certain parameters (such as a length feedback gain or offset) will produce some effective torque about the right ankle joint. This torque could instead be generated by a DOF actuator, if given the correct actuation when the muscles are set to false output.

Is there a way I can "convert" a specified torque to a specified excitation magnitude? Is this related to the actuator's "optimal force"? Also, is there documentation of how the total force of a muscle is calculated based on its values for speed, length, etc.? If not, is there a way in OpenSim that I can easily test different excitations of muscles and joint actuators to find what force/torque they produce?

Thank you for any and all information.

[Carmichael Ong]

Yes, there is documentation for our muscle classes and how force is calculated from the muscle state. A few examples from the most common muscle types:

Thelen2003Muscle:
https://simtk-confluence.stanford.edu/d ... scle+Model
https://simtk.org/api_docs/opensim/api_ ... ml#details

Millard2012EquilibriumMuscle and Millard2012AccelerationMuscle:
https://simtk-confluence.stanford.edu/d ... cle+Models
https://simtk.org/api_docs/opensim/api_ ... uscle.html
https://simtk.org/api_docs/opensim/api_ ... uscle.html