Unreasonable force plate results in Plug-in-gait_MultiTrial using GRFPrediction

Hi,
I'm using Plug-in-gait_MultiTrial and I have added the ForcePlates_GRFPrediction file to the model. Moreover, I have modified the directions of the force plates and the gravity. The subject is in standing posture and weighs 80 Kg. The problem is that the normal component of the FGlobal parameter of each force plate is around 40 N, although it should be approximately 400 N.
I have modeled the same C3D file with the Plug-in-gait_Simple model using the FullBody_GRFPrediction.main file. Everything is fine, and there is no problem with this modeling.
Is there any possibility that this problem occurred because I have replaced the ForcePlates.any file with the ForcePlates_GRFPrediction.any file in the LabSpecificData.any without further modifications?

Best regards,
Mohammadreza

That would be great if someone could help me with this. :slightly_smiling_face:

Hi @mrb9

It is probably due to the HumanGroundResiduals.
There is a switch to control wich segment to apply these to (Pelvis or Thorax). But when using the GRF prediction tool it has to be implemented as weak residual forces. So you can use:
#define MOCAP_HUMAN_GROUND_RESIDUALS "PelvisWeak" in the labspecificdata.any file. This should help your issue.

I am not sure what gravity you changed, but it should be enough with the NormalDirection of the GRF prediction classes and to ensure that the feet are close enough for contact.

Best regards
Bjørn

1 Like

Hi Bjørn,
Thanks for your answer. I'm going to implement that.

Best regards,
Mohammadreza