Contact Forces

[William Lee]

Hi OpenSim Team,

I am currently trying to implement contact forces for my model, and I have looked at the tutorial covering it with the bouncing ball and ellipsoid; however, I am trying to implement contact forces that allow my model to remain still on the ground. I don't want to weld my model onto the ground because I want it to be able to traverse the ground following a rectilinear motion. Is there a specific force type I should use or property value I should tweak in order to have contact forces on my model without a bouncing motion?

[Thomas Uchida]

I want it to be able to traverse the ground following a rectilinear motion

You could attach your model to Ground via a SliderJoint (https://simtk.org/api_docs/opensim/api_ ... Joint.html) or constrain it using a PointOnLineConstraint (https://simtk.org/api_docs/opensim/api_ ... raint.html).

[William Lee]

Thanks for the suggestions, but is there anyway to remove the bouncing force from the huntcrosselyforce? I would ideally like to use contact spheres for the points on my model that make contact with the ground.

[Thomas Uchida]

is there anyway to remove the bouncing force from the huntcrosselyforce?

You could increase the dissipation coefficient. Please see Section 11.2 in the Simbody theory manual: https://github.com/simbody/simbody/tree ... imbody/doc.

[William Lee]

Increasing the dissipation coefficient seemed to help, but the model I have slowly tilts forward when I run an in-place motion, a motion that should allow the model to remain standing still. Also, I have decided to use contact meshes for the model as opposed to contact spheres to see if it would make a difference, but I still experience the same issue of having my model tilt forward.

Do you have any suggestions on how I can have my model remain standing still without bouncing or tilting forward using contact forces? For example, if the object in the bouncing ball tutorial was instead a bouncing cube, would it be possible to remove the bouncing motion and simply have the cube sitting up straight without falling over.