Hello,
I'm currently working on a model of human-device interaction, where the device is constructed as two beams with common rotation axis, where both feet are attached to the free ends of both beams. It's the MoCap-driven model, where both human and device kinematics are driven by markers. It's the movement of lifting the knees up. The GRF prediction was implemented on both feet within the body-device interaction area, with the beam ref frame as a PLATE_BASE_FRAME. I also used the modified GRF prediction for the beams-ground interaction and for the axis-ground interaction. The feet-beams interaction is also constructed similar to the CrossTrainer example with the use of joints. The device is also connected by joints and moves well in marker tracking. I made all the necessary steps according to the GRF prediction documentation.
My marker tracking analysis goes well but the inverse dynamics study breaks with the OBJ.MCH.KIN1 error: Model is kinematically indetermined.
How can I fix it?
I am not really able to imagine your model, but my guess is that somehow your model is not included in the inverse dynamics study. The error states that. All the joints and segments that you have made for your device are probably included in only the marker tracking study.
Can you please check if this is the case? To fix this, you can open the scope of the inverse dynamics study and include reference to the folder containing your model.
You're right.
So I figured out that indeed, my device segments position was not implemented in the inverse dynamics study. I made some additional coding based on the mocap example with the box. The method worked for my model with the bar with loads placed on the shoulders but when I used that for this model, the error now shows my model is kinematically over-constrained. When I use a diffrent solver, the study breaks in step 0 too.
I think, it's simply a question of counting the degrees of freedom and constraints. You want to have the same number of constraints as the degrees of freedom. I would suggest making a simple sketch and determining all the constraints that you need for your device and then implementing them in AnyBody. From your message, there are too many constraints that you have added, and the kinematics can't be solved.
An alternative could be to use the over determinate solver, but I don't think it's needed. And it can still break if you have constraints that conflict with each other.