Hi there,
The results of joint moments I got from Inverse Dynamics are very weird. The patterns of joint moments in knee and ankle are the same, which should not happen. I have checked the joint angle results and external loads file, and set the Inverse Dynamics tool as in manual. Is there any factors could lead this problem?
Any advice would be helpful.
Inverse Dynamics error
Inverse Dynamics error
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Dimitar Stanev
- Posts: 1096
- Joined: Fri Jan 31, 2014 5:14 am
Re: Inverse Dynamics error
It seems that in the region of ~2.6 to ~3.24 you are computing very large moments. It is possible that in the rest you are computing normal values. This can be caused by some discontinuity in your external forces or the kinematics (from Inverse Kinematics). Note that ID uses higher order derivatives of the kinematics (velocity and acceleration) along with the position in order to evaluate the moments. There may be a problem when the derivatives are computed (splines are used).
Re: Inverse Dynamics error
Hi, Dimitar,mitkof6 wrote:It seems that in the region of ~2.6 to ~3.24 you are computing very large moments. It is possible that in the rest you are computing normal values. This can be caused by some discontinuity in your external forces or the kinematics (from Inverse Kinematics). Note that ID uses higher order derivatives of the kinematics (velocity and acceleration) along with the position in order to evaluate the moments. There may be a problem when the derivatives are computed (splines are used).
Thank you for your reply.
May I ask another question about ID? During calculating the joint moments, no matter how I set the Inverse Dynamics Tool (including where the loads applied to, where the force and point expressed in), it always get the same results. What mignt be the cause of this?
Looking forward your reply.
Thanks
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Dimitar Stanev
- Posts: 1096
- Joined: Fri Jan 31, 2014 5:14 am
Re: Inverse Dynamics error
Probably you are not setting the external force correctly or the motion is problematic. Can you load the motion? Also look at the message to see if everything is ok with the ID tool. Did you tried the OpenSim examples to see how they setup the ID tool, maybe you are missing something.
Re: Inverse Dynamics error
Yes, I've tried the examples. But the external load data in example file confused me. May I ask where the reference point of moment calculation is in example file? Because the patterns of ground reaction moments are very different from what I've got.mitkof6 wrote:Probably you are not setting the external force correctly or the motion is problematic. Can you load the motion? Also look at the message to see if everything is ok with the ID tool. Did you tried the OpenSim examples to see how they setup the ID tool, maybe you are missing something.
Re: Inverse Dynamics error
If you haven't already, try previewing your ground reaction forces in the GUI and double check the units for the GRF data. If, for example, your center-of-pressure (COP) is in mm vs. m, or force-plate moments are reported in N*mm your computed moments will be enormous (like what you are seeing). If the COP units are incorrect, the previewer will show the forces being applied at some distant point and not under a foot.