FDK Error


Hi All,

I was wondering if any of you would help me. I am creating a simple FDK model using wrapping muscles and I am getting the following error " Too small steps for GSS search causes looping of Newton method ". I have two wrap muscles, and it seems one of them “supraspinatus” is causing the issue because when I turn it off Inverse Dynamics work just fine.

I have attached the code and I would really appreciate it if someone can run it and give me their feedback ASAP. It is a really simple model anyhow.



Hi Mohammed,

I have not looked at the actual model, but usually wrapping problems may occur if the string is about to slide of the ends of a cylinder. So if this can be the reason try to ensure the string hits not on the cylinder end but somewhere in the middle.
A second remedy can be to increase the StringMesh property this can also help.

Last thing can be alter the initial position of the vector which controls how the string is wrapping initially, so essentially which way it will take around the object. This is controlled though the initwrappos vector.

see also https://github.com/AnyBody/support/wiki/Model-trouble-shooting#resolve-wrapping-problems

Hope it helps
Best regards


Hi Mohammed,

I now realize that the GSS error is not related to wrapping sorry for this.

This error means that the solver can not find a way to balance the FDK DOF in the model.

In general there can be these reasons for it

[li] The definition of stiffness can in general potentially be a source of error
[/li][li]Muscle configuration may be wrong, eg. are the surfaces the muscles are wrapping on attached to the correct objects? this may alter force balance significantly.

Hope it helps

Best regards