Help with Collision Bodies

[Andrew Bossert]

Hello,

I am in the early stages of learning OpenSim modeling for my upcoming degree program and I am a bit confused about setting up object collision in Creator.

I have downloaded a head/neck model (Musculoskeletal Model of Head and Neck Suitable for Dynamic Simulations) from the project database that I was hoping to adapt to my work. Currently I am setting the model in a supine position with the head tilted up to an elevated position (chin-to-chest) and I would like to create contact geometry between the skull and the floor. I have created a ContactHalfSpace for the ground and a ContactSphere for the skull (placed roughly at the geometric center and sized to fit the skull as closely as possible). Following the example "2. Make a Bouncing Block" found in the OpenSim Creator documentation, I added the contact geometries to a HuntCrossleyForce with the default values. Upon simulating the environment, the skull (and its attached contact geometry) passes through the ground ContactHalfSpace. My expectation was that the skull would impact the ground and, after brief restitution, come to rest on the plane. At the very least, this is what I would like to achieve with a simple simulation.

If I have missed a step in the process of defining contact geometry or have otherwise made a mistake somewhere in this process, I would appreciate any help with troubleshooting this.


Thank you!

Andrew Bossert,
Boise State University

[Jon Stingel]

Hi Andrew,

In order to help debug, it might help to see the model file that you are working with, including the edits and additions that you have made. Just double checking, you are able to load the model with 1) the ContactHalfSpace for the ground, 2) the ContactSphere for the skull, and 3) the contact force in the forceset? If so, as the tutorial mentions, the half space only collides on one side, so perhaps you can check your orientations for the contact geometries to see if they are defined differently.

Hope this helps!
Jon

[Andrew Bossert]

Jon,

Thank you for the reply. I had missed the part about the sidedness of the half-plane, and sure enough mine was oriented the wrong direction! I swapped it 180 degrees around and now the skull rests nicely on the ground. This also explains why my simulations were taking a tremendous amount of computing power as the contact geometries were stuck inside one another . Thank you again for the help!


Andrew Bossert
Boise State University

[Jon Stingel]

Awesome! Glad you were able to get it working. Looking forward to seeing your study!

Jon