Apply translation to mechanical object

Hi Jonny,
I had a similar problem and the SoftRobots tutorial on the tripod was incredibly helpful.

Have a look at the setupanimation function here:
https://github.com/SofaDefrost/SoftRobots/blob/master/docs/tutorials/Tripod/details/tripodcontroller.py

If you can use the splib, great! If not, you may want to copy out the relevant snippets of code from there. 😉

Cheers,
Paul

Hi @jonny,
I just had a look at the files.

My intuition would be to create a MechanicalObject with the Rigid3d template (so you only have to set one position value to move the floor, and not every position for each node. And then use a RigidMapping between this MechanicalObject and your collision and visual models.

###Creating the floor
floor = rootNode.addChild(name)
floor.addObject(
    "MechanicalObject",
    name="mechObject",
    template="Rigid3",
    translation="0 0 -30",
    rotation="90 0 0",
    )

###VisualModel
floorVisu = floor.addChild("VisualModel")
floorVisu.addObject(
    "MeshObjLoader", name="loader", filename="mesh/floor.obj", scale=1
)
floorVisu.addObject("OglModel", name="model", src="@loader", color=[0.8, 0.8, 0.8])
floorVisu.addObject("RigidMapping")

###CollisionModel
floorCollis = floor.addChild("collision")
floorCollis.addObject(
    "MeshObjLoader",
    name="loader",
    filename="mesh/floor.obj",
    triangulate="true",
    scale=1,
    )
floorCollis.addObject("MeshTopology", src="@loader")
floorCollis.addObject("MechanicalObject")
floorCollis.addObject("TriangleCollisionModel",)
floorCollis.addObject("LineCollisionModel")
floorCollis.addObject("PointCollisionModel")
floorCollis.addObject("RigidMapping")

That might speed things up a little. At least for moving the floor.

Hi @jonny,
I’m glad that helped! 🙂

For the deforming floor, you could try setting appropriate flags in the collision model to tell sofa that these models are supposed to move, but not deform.

floorCollis.addObject("MeshTopology", src="@loader")
floorCollis.addObject("MechanicalObject")
floorCollis.addObject("TriangleCollisionModel", simulated="false", moving="true")
floorCollis.addObject("LineCollisionModel", simulated="false", moving="true")
floorCollis.addObject("PointCollisionModel", simulated="false", moving="true")
floorCollis.addObject("RigidMapping")

Sadly I do not have any (successful) experience with any of the Constraints. 😀
But introducing a ForceField was pretty sufficient for my use cases. As @hugo said in the post, it does not ensure, that the points will be at the exact same location. But that really depends on the use-case, right?

Maybe try using BoxStiffSpringForceField. This one will take the indices of both objects from their respective boxes and create springs between them.

Hi @jonny,
alright, I am looking forward to it!

You are very welcome. 🙂

Cheers,
Paul

Hi @jonny

The topic you pointed out indeed explains the theoretical difference between the two methods: AttachConstraint vs BilateralInteractionConstraint.

With the PartialFixedConstraint, you can indeed choose which vertices and which dofs of theses vertices to fix.

To answer your last point, I would need a global understanding of what you want to achieve when you say “connect the two models”.
I think what was meant in my comment is that : if you want to connect both objects they have to have the same DOFs types (template). Which is not your case I guess: one object is rigid while the other one is deformable. An alterantive is to simply create a sub-node for the rigid object (connected using a RigidMapping) containing one deformable DOF, e.g. Vec3d.

I hope I am clear enough. If not, please let me know.
Best wishes,

Hugo