Jacobian between two joints

[Ali Khalilianmotamed Bonab]

Dear OpenSim Experts,
I assigned an actuator to the torso and now want to get its torque profile in another frame.
I would be grateful if you could help me with the following issue:
Is any specific command in OpenSim API to do this transformation? If there is no such command, is it possible to get the jacobian between two joints to do this transformation?
Many Thanks,
Ali.

[Dimitar Stanev]

Hi,

The question is a bit fuzzy (what do you mean by joint Jacobian?). I will assume that you are interested in calculating the Jacobian that relates a task space force and generalized forces or the their kinematic counterpart:

tau = J^T f or x_dot = J q_dot

If you know the point of application and the body then you can calculate the Jacobian:

https://simbody.github.io/simbody-3.6-d ... 71101927f3

You can see examples that make use of these Jacobians in the following repository:

https://github.com/mitkof6/task-space/b ... icTask.cpp

[Thomas Uchida]

The following resources may also be useful:
- "Interactive Operational-Space Controller for OpenSim" (a student project): https://simtk-confluence.stanford.edu/d ... or+OpenSim
- "Operational-Space Controller API Tutorial", which includes example code (in the "Get the API files" section): https://simtk-confluence.stanford.edu/d ... I+Tutorial