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Hello everyone,

I'm using Gait 2354 to analyse driver's lower body movement during emergency brake. Scaling and IK were done. But I got stuck by Inverse Dynamics with .mot file, since I only have the magnitude of the brake force, but not force position and force direction. Thus, I have to create a .mot file by my self to excute the ID.

So I wanted to use this workaround: create a new Marker on the middle of the ball of foot, which could be assumed to be the contact point on brake pedal, and export its trajectory (in global axis system) as the force position in .mot. Then combine this .mot with the force data.

But I cannot find any option in OpenSim to export trajectory of a marker.

Do I need MATLAB API to do this? Maybe you have a much better solution. Thank you very much.

A picture of my model is attached.

Best regards,
Yanlong

I'm not sure if this is what you're looking for, but perhaps instead of finding the point's location in the global (ground) frame, you can just provide a point (and possibly also force) in the frame of the foot. When you're loading an ExternalForce file, you can change what the Force and Point are expressed in:

Hi Carmichael,

thanks for your reply!

I'm not sure if I understand it correctly: I can load a external force file in .mot WITHOUT specification of the force position (i.e. force_px, force_py, force_pz), then edit it to apply on a body part (like toe or calcaneus)? I'll definetly try this.

Before I got this reply, I also tried another method. There is indeed a workaround to export a certain manually modeled marker in .sto by using "Tools->Analyze->Analyses->Add->PointKinematics", like this: It then can be merged in the external force .mot file.

Best regards
Yanlong