Joint in Opensim Model

[Hilary Cheng]

Hi,

I would like to know how the Custom Joint relating to Spacial transform in terms of formulation. Is there any paper talking about that?

In Opensim GUI, I found that a coordinate(elv_angle) is trying to Rotate the axis of another coordinate(shoulder_elv).
When I read the attached .osim file, I cannot identify the pattern for the above relationship. Which part of the .osim file stated the relationship between joints/coordinates?

Thanks!!

Regards,
Hilary

[Dimitar Stanev]

A custom joint is a wrapper around Simbody's function based mobilizer:

https://simbody.github.io/simbody-3.6-d ... ml#details
https://simbody.github.io/simbody-3.6-d ... ml#details

Doxygen:

"When you create it, you specify the number of generalized coordinates, and six Function objects which calculate the spatial rotations and translations based on those coordinates."

publication:

https://simtk.org/docman/view.php/47/15 ... 2-p291.pdf

Then you can also create relationships between the general coordinates. This is achieved through constraints (e.g., CoordinateCouplerConstraint).

[Ajay Seth]

The SpatialTransform in OpenSim describes how the Child frame moves with respect to the Parent frame of a CustomJoint. It specifies the permissible movement (by user provided functions) on 6 axes (3 rotational and 3 translational TransformAxes) parameterized by generalized coordinates (the joint's coordinates). See: https://simtk-confluence.stanford.edu:8 ... els-Joints