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Hello, I am trying to link an otrhosis to the lower limb of an OpenSim model. As my aim is to simulate the most realistic interaction between the leg and the orthosis I was thinking of implementing a spring, which properties would be able to mimic some kind of skin and soft tissue movement.

I do not want to model the interaction as a weld joint or weld constraint, I would like a PathSpring or another type of Spring between the point of the orthosis and the point of the leg that I want to link. My question is the following

Is there a way to define a spring between 2 point of my choice and not along a muscle or a body?

All the examples I have seen in the documentation define the PathSpring along a muscle and use its geometry, so I do not know if I can choose 2 arbitrary points.

Is there any better way to link 2 objects in OpenSim to simulate certain relative movements between two bodies?

By the way, I am avoiding to use contact models because I have seen that they do not perform well on static optimization or CMC and those are features in which I am interested.

Thank you very much.

Best regards.

In that case, I think you can you PointToPointSpring.

Using PointToPointSpring you can make spring force between arbitrary two points you want with specific stiffness and rest length.