Trunk tutorials：How to get translational motion in a cable-driven finite element model?

[TurboS2002]

I'm creating a finite element simulation in sofa similar to Trunk tutorials and I was wondering how to create controllers for the keyboard to control its translational motion?

[EulalieCoevoet]

Hello @TurboS2002,

Sorry for the late answer.

To help you code the keyboard control, you can have a look at the Tripod tutorial. There's this controller that may help you.

If you also have troubles with the trunk's translation motion, I can think of two approaches:

1. You can replace the PartialFixedProjectiveConstraint by a RestShapeSpringsForceField in:

def fixExtremity(self):
        self.node.addObject('BoxROI', name='boxROI', box=[[-20, -20, 0], [20, 20, 20]], drawBoxes=False)
        self.node.addObject('PartialFixedProjectiveConstraint', fixedDirections=[1, 1, 1], indices='@boxROI.indices')

And then translate the rest positions from your controller. For example:

with TRUNK_NODE.getMechanicalState().rest_position.writeable() as rest_position:
    for position in rest_position:
        position[TRANSLATION_DIRECTION] += step

2. (more advanced) Rigidify the part of the trunk selected by the BoxROI. There's also an example in the Tripod tutorial here. And then use the same approach with the RestShapeSpringsForceField and the controller, but this time only on the resulting rigid frame.

[TurboS2002]

Hello and thank you for your reply! I am using SOFA version 23.06.00.
I found in the Trunk tutorial that the code is

  def fixExtremity(self):
       self.node.addObject('BoxROI', name='boxROI', box=[[-2.5, -2.5, 0], [2.5, 2.5, 4]], drawBoxes=True)
       self.node.addObject('PartialFixedConstraint', fixedDirections=[1, 1, 1], indices='@boxROI.indices')

PartialFixedConstraint instead of PartialFixedProjectiveConstraint or RestShapeSpringsForceField . Is this a version issue?
As well as the cableconstraints and translational motion combination routines?
Thanks!

[TurboS2002]

@EulalieCoevoet Hello，Thanks for your reply！
I am trying to build a catheter in sofa that can achieve keyboard-controlled mobile delivery and cable-driven controlled bending, I have achieved cable-driven controlled bending, but achieving movement is very difficult for me.
I tried to make a part rigid and then change the position of the rigid part, but only the rigid part moved while the deformable part did not change. I think there may be some problems in the mapping, but I can't find the specific problem. Below is my code and mesh, thank you for your help!
learn_sofa.zip

[hugtalbot]

PartialFixedConstraint instead of PartialFixedProjectiveConstraint or RestShapeSpringsForceField . Is this a version issue?

Yes, PartialFixedConstraint has been renamed as PartialFixedProjectiveConstraint
@TurboS2002 Make sure to post focused questions so that we can help you at best
To get started always follow the available tutorials : Introduction Course

[ozilxu]

@EulalieCoevoet Hi Eulalie, can I also ask if we only change fixedDirections=[1, 1, 1] to fixedDirections=[0, 1, 1] in self.node.addObject('PartialFixedConstraint', fixedDirections=[1, 1, 1], indices='@boxROI.indices') to achieve the translation in the base? Thanks

[hugtalbot]

Hi @ozilxu

Never hesitate to open new discussion topic instead. Even for small questions.
In PartialFixedProjectiveConstraint, the data fixedDirections defines which DOFs are constrained to remain fixed : [0, 1, 1] means that y- and z- degrees of freedom (DOF) are fixed while the point can move freely along the x-axis. Does this make sense?

Cheers

[ozilxu]

Hi Hugo, Thanks for your answer! I will open up a new discussion on the Github