Adding Contact surface meshes to mapped system

[Arthur]

Hello @Hugo, @felixvanneste,

My short term goal is to get surface mesh collision on a mapped node instead of just point collision.

My long term goal is to be able to reuse a leg several times for a robot, where I only need to use model order reduction once on the leg. I am using the Sofia example in MOR as a template to work from. (https://github.com/SofaDefrost/ModelOrderReduction/tree/master/doc/examples/SOFIA)

However instead of legs like the ones used for SOFIA I am using Pneunets and so I need to have collision detection along the length of the legs. I have tried using only the points on the bottom of the legs (see attached scene) however I don’t think this is enough to keep the robot stable on the floor.

I was thinking one way to fix this would be to have a full collision surface (one that you would load through an STL file). Mine would be volume_collision.stl which is attached. I can get it to appear on the original leg position, but I am not sure how to properly map it to the mapped position of the leg. I think it would be at the point in the scene.py file that I haved marked with “COLLISION”. Files here: https://uchicago.box.com/s/um1611rig6riasr9d9o1ac7rdzsdi1x0

How can I do a mapping like this? Or is there another way you suggest to have a more robust collision model along the bottom of the mapped leg (I am hoping not to need a much denser mesh as runtime is already an issue, hence why I want to do model order reduction on this next).

I am also not quite sure how the mapping works — moving the robot with my mouse does not cause the legs to flop around as I would expect. At one point I thought a BilateralInteractionConstraint would be best for my situation, but I was not sure how that works — another solution for me might be just getting that to work, but I am not sure how to do that either.

Build details can be found here:https://github.com/ripl/SofaFramework-Docker/blob/6dcde34d6ee9550635d53478971f2fb0b62d5d5a/Dockerfile

[Félix]

Hello @amackeith,

I don’t totally see what you want to do with the mapping but I can recommend you to look into the MultiGait-SoftRobot example in the doc which seems to correspond to what you are trying to do (pneumatic actuation with collision).

But at first glance I will use the volume_collision.stl to have triangle for the collision, I have to admit that I don’t really know if you can do proper collision with only point… Anyway if you find the volume_collision.stl to heavy you can always sub-select it or generate a new surface mesh with only the surface you are interested in.

I hope this help you,
Félix

[Arthur]

Thanks @felixvanneste,

My problem is that I do not know how to get the triangular collision mesh from volume_collision.stl to appear on the leg on the robot. Rather it appears on the leg the is in a fixed position. (I need it on the one that is in the mapped position). The the example this is from gets the points to be mapped with:

# mapped collision (with reduce size)

        mappedCollisionLeg = mappedLeg.createChild('mappedCollisionLeg' + str(i))
        mappedCollisionLeg.createObject('MechanicalObject', template='Vec3d',
                                        name='mappedCollisionLeg')
        mappedCollisionLeg.createObject('Point', color='1 0 0 1', group='1', translation=framePosition[i])
        mappedCollisionLeg.createObject('SubsetMapping', indices='@../../../' + strLink0 + strLink1 + str(
            i) + strLink2 + '/boxROICollision.indices',
                                        input='@../../mappedLeg' + str(i) + '/mappedLeg')

And I was wondering how to do this kind of mapping but also include triangles (or have the collision mesh be there).

I was also wondering if there is a reason “BilateralInteractionConstraint” was not used in the SOFIA demo where the mappings are used instead? Is there any reason that “BilateralInteractionConstraint” would not work with a reduced model?

Arthur

[Hugo]

Hey @amackeith

Your scene looks nicely complicated, well done!
The idea of selecting only a subset of point for the collision is cool and should work well.

However, the collision model of each leg should appear as the child node of this leg.
Before going further, I would make sure that modeling only one leg (without rigid body or anything else) you can have a proper collision detection and response.

Then, creating a rigid part and connecting it with these legs should be easier.
Did you get inspired from the MechanicalMatrixMapper scene?

Best

Hugo

[Author]

Posts