simtk.org

Hello, I am attepting to modify the gait2392 model to create a closed chain movement pattern. This is to be used to simulate snowboarding where both feet are fixed relative to the board by non-release bindings.

To do this I have created a joint between each foot and the 'ground' and reversed the order of the segment parent-child arrangement so the proximal segment moves relative to the distal segment (e.g. tibia moves forward over foot during dorsiflexion).

I can achieve this for the individual limbs however when i get to the pelvis I strike a problem.... As far as I know I can only use one segement as the parent of the pelvis (either right or left femur) and thus I cannot create both hip joints.

I would like the relative position of the femurs to dictate the position and orentation of the pelvis in space.

If anyone has dealt with this problem or has any pointers I would be greatly appreciative.

Regards

Paul McAlpine

You can use the gait2392 model and add WeldConstraints to affix the feet to the board.
Add something like the following to the ConstraintSet:


<WeldConstraint name="">
<isDisabled> false </isDisabled>
<body_1> board </body_1>
<body_2> calcn_r </body_2>
<location_body_1> 0.0000000000 0.000000000 0.0840000000 </location_body_1>
<orientation_body_1> 0.0000000000 0.0000000000 0.0000000000 </orientation_body_1>
<location_body_2> 0.000000000 -0.0200000000 0.000000000 </location_body_2>
<orientation_body_2> 0.0000000000 0.0000000000 0.0000000000 </orientation_body_2>
</WeldConstraint>

Thanks Ajay, thats a great help.

Have have successfully attached the right calcaneus to the board but I am having issues with the left calcaneus - irrespective of the location coordinates that I enter for either body the left calcaneus ends up in the same location as the right one in the opensim program.

Any suggestions?

Kind Regards

Paul

This appears to be a problem with Open Sim version 1.8.1. If I use version 1.8 I can weld both feet to the board with no probelms

Thanks again

Paul

Hi,
What exactly means tags <location_body_1> and <orientation_body_1> (and for the second body as well) ?

Michala

Hi, Michala. Those parameters specify the location and orientation of a coordinate frame attached to each body. Then the weld constraint acts to hold the origins of those two frame in the same spatial location, and to align their axes. So if you leave those at their default values (0,0,0) the frames will be coincident with the body frames, and the weld constraint will act to hold the body frames of each body coincident.

Regards,
Sherm