OpenSense - Delsys IMUs

Provide easy-to-use, extensible software for modeling, simulating, controlling, and analyzing the neuromusculoskeletal system.
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Rodrigo Bini
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OpenSense - Delsys IMUs

Post by Rodrigo Bini » Thu Jun 22, 2023 9:44 pm

Hi,
I am working on a project to use the Delsys IMUs to drive IK in OpenSense and wanted to check if questions are being taken for this topic. The OpenSense stand-alone forum seems to be locked so I thought I would check first.
Thanks,
Rodrigo

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Ayman Habib
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Re: OpenSense - Delsys IMUs

Post by Ayman Habib » Thu Jun 22, 2023 10:45 pm

Yes Rodrigo, this forum supports OpenSense.

Welcome aboard,
Ayman

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Rodrigo Bini
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Re: OpenSense - Delsys IMUs

Post by Rodrigo Bini » Sun Jun 25, 2023 3:43 pm

Thanks Ayman for the prompt response.
I adapted some codes to generate quat orientations from IMU data collected from Delsys (acc, mag and gyro). I managed to place the sensors in the model and ran the IK-IMU. However, the motion was unrealistic and wanted to check the following:
1- Does the orientation of the IMUs that we see in the model influence how IK derives angles?
2- As I assume a 'yes' for the above, how do I check the orientation of the IMUs? I noted that I can change the placement and orientation of each IMU but wanted to know the definition of the coordinate system (i.e. x-y-z) for each sensor.

Happy to share sample data and code if that helps.

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Ayman Habib
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Re: OpenSense - Delsys IMUs

Post by Ayman Habib » Mon Jun 26, 2023 8:38 am

Hi Rodrigo,
To answer your questions:
1. Definitely, the job of IK is to find coordinate values that position the model to match as close as possible the orientation of the "placed" IMUs with the measured orientations in provided input files/tables.
2. You can see the orientation of the placed IMUs in the OpenSim application by expanding the navigator tree to the specific imu (e.g. Bodies/femur_r/femur_r_imu), then select "Show Axes" from the context menu of the relevant imu. You should see a triad representing orientation (Red-Green-Blue for X-Y-Z)

Assuming you recorded or have a picture of how the imus were placed on the subject during data collection, you can compare that to the orientation computed by the IMU placer (item 2 above). I'd argue that if there's mismatch then proceeding to do IK would be unlikely to produce correct answers since it would be based on incorrect assumptions.

Hope this helps,
-Ayman

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Rodrigo Bini
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Re: OpenSense - Delsys IMUs

Post by Rodrigo Bini » Mon Jun 26, 2023 4:36 pm

Wonderful. Thanks Ayman. I think we can get this right and should be able to share some resources for others.

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