Ground contact modelling

[hesam boroomand]

Hello to everyone
I am working on gait simulating of an amputee using prosthesis (Amputee with prosthesis model from https://simtk.org/projects/bkamputee_model). In my simulation, I had previously done CMC and forward dynamics using available gait markers and GRF data on OpenSim directory (in GUI). With CorrectionController I gained nice results and stable gait (one cycle). Recently i tried to add ContactSphere and HalfSpace in order to model ground contact, so I wouldn't need using GRF data. However my model collapses and doesn't continue walking. How can I enhance my ground force modelling ? and it it totally possible to use modeled GRF in simulation?
Thanks a lot