Difficulties with CMC and multiple kinematic loops in the model.

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Sietse Achterop
Posts: 81
Joined: Tue Sep 14, 2021 3:01 am

Difficulties with CMC and multiple kinematic loops in the model.

Post by Sietse Achterop » Wed Nov 20, 2024 3:20 am

Hello list,

My model of a rower in a boat has progressed a bit!
Please find the model and all data attached.
But regrettably I now again have a problem with CMC.
rower.png
rower.png (329.87 KiB) Viewed 322 times
The model now has 2 kinematic loops implemented using WeldConstraints at the foot stretcher
and the starboard outrigger.
The previous version, without the lower arm and oar, now works perfectly with CMC.
I can see 2 issues/questions.
Does the presence of 2 kinematic pose an extra problem?
And of course, which tasks have to be set in bb_CMC_Tasks.xml.

With CMC and the current bb_CMC_Tasks.xml, the simulation fails after 0.91 second.
In fact between 0.91 and 0.93 CMC seems to finds another solution (more or less), this because
there is no task connected to the elbow joint.
With FailCMC.mot you can see the failing occur, and logCMC is some output from opensim.
So this setting is not correct, but which setting is?

I have tried almost all possibilities, but nothing works.
What am I doing wrong here? Is there still something problematic in my model or trajectory?
How do I determine which tasks to use in CMC given the kinematic loops?

Thanks in advance,
Sietse


PS. There also is something strange in the GUI.
You can single step a motion, and it steps accordingly. But e.g. with FailCMC.mot the steps become very small at the end.
Stepping back from the end-time, you can see the model stapping back, but the time indicator does not move for a very long time!
I assume that this is because the simulation tries to solve it by making its steps smaller and smaller. Correct?
Attachments
BootBaan1.zip
(410.22 KiB) Downloaded 7 times

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User avatar
Sietse Achterop
Posts: 81
Joined: Tue Sep 14, 2021 3:01 am

Re: Difficulties with CMC and multiple kinematic loops in the model.

Post by Sietse Achterop » Wed Nov 27, 2024 4:42 am

Got it to work!
Changed a few things:
  • Changed the connection between hand and oar to reduce some coordinate values to well below 90 degrees
  • Set the task for the leg to the knee instead of the seat
Added the model again for completeness.
Regards, Sietse
Attachments
BootBaan1_OK.zip
(550.52 KiB) Downloaded 29 times

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