Reference Frames, Inertia Expressions, Body Definitions

[Ali Khalilianmotamed Bonab]

To Whom it may concern,
I have some very important questions about OpenSim that are very necessary for my research so I would appreciate if anyone can help me with them.

1) When we are running the RRA it generates joint moments and some other data. I want to know the reference frame that has been assigned for this data or more explicitly, what is the reference frame for Joint Moments Data.

2) We are defining two different torque actuators which are acting from body A to body B and body C to D and torque is not global, I want to express both of the torques in the same reference frame (A). How can I do these transformations?.

3) When we are deriving the Muscles moment, what is the reference frame for expressing the moment and if I am, for example, expressing muscles acting on Hip joint, are all the muscles have the same reference frame? Secondly, if Muscle Moments for each joint has different reference frames, how I can express Muscles Moment in the same reference frame like the ground?

4) About the TorqueActuator, When I am assigning for instance from the femur to tibia, is it affecting the knee and ankle joint or is it just acting on the joint between two bodies? More clearly, In the mentioned configuration, Does it actuate all the joints related to the bodies like ankle hip and knee?

5) About Body Definition on the Opensim, I want to define a Body on the specific joints, For instance, I want to have a body on the Knee Joint, I am defining it as a weld joint which connected to Tibia or femur, then I am using the Transformation matrix to transform it on the joint.

- Is this the correct way of assigning the body on the joints?
- The assigned body has mass and inertia, are they affecting on the assigned location or they just acting on the parent
body

6) Inertia Calculations on the OpenSim, As it is explained, I have some bodies defined in the lower limbs and from the parallel theorem, we know that they will reflect on the upper bodies, Are these reflected inertias automatically calculated by OpenSim or we have to manually change inertias on affected bodies?

The questions may seem to be very basic but fundamental and important for me because they cause serious difficulty for me, So, I would be grateful if you can not only answer these questions but also introduce references for OpenSim that explains all these fundamental properties clearer than OpenSim API.


Looking forward to getting the answer of my questions as soon as possible.
Many Thanks,
Ali.

[Ali Khalilianmotamed Bonab]

Dear Opensim Developer,
I would kindly appreciate you if you can help me with the mentioned issues, I have read some papers but I really need to make sure about this issue to be able to have correct interpretations about our results.
Sincerely,
Ali.

[Thomas Uchida]

6) Inertia Calculations on the OpenSim, As it is explained, I have some bodies defined in the lower limbs and from the parallel theorem, we know that they will reflect on the upper bodies, Are these reflected inertias automatically calculated by OpenSim or we have to manually change inertias on affected bodies?

Please see the publications listed here: https://simtk-confluence.stanford.edu/d ... ics+Theory.