23 March 2020 at 15 h 36 min #15527
Hello! I’m trying to build a simple system with a soft inflating object. I’ve built up a cube with a cavity and have then applied the following for the actuation:
cavity.createObject('SurfacePressureConstraint', name='SurfacePressureConstraint', template='Vec3d', value='0.0001', email@example.com', valueType='pressure')
The issue is that when I don’t have the object fixed at any point the forces on the surface doesn’t reveal to be symmetric, while my object’s geometry is symmetric. Instead it rotates upon inflation (I was considering the system without gravity to see how solely the forces acted on the object). I initially thought it was an issue related to the mesh I may have used as well as the surface normals of that mesh. But have found that it is not related to the mesh. And then when I was experimenting with the example in the Soft Robotics plugin of the pneumaticGripper I found similar behaviour. When removing the static constraint(BoxROI) and setting gravity to 0 0 0 in step6 it also began to rotate when inflated.
I’m confused about this rotation. I’m guessing its related to the Surface Pressure Constraint as there are no other external forces. Furthermore, how do I get rid of it? In the end I want to let my object inflate and move on a surface so I cannot incorporate a static box. Would highly appreciate advice! Thank you!24 March 2020 at 11 h 45 min #15537HugoKeymaster
- SOFA Consortium
The component you are referring to is located in the SoftRobot, correct?
I therefore don’t know its code.
However, as all pressure components, its effect is obviously mesh-dependent. I would have also thought about a mesh issue. What tells you that it isn’t one?
The rotation you notice can come from the asymmetry of your faces thus creating a momentum on your object due to unbalanced forces.
Which mass are you using?
Hugo25 March 2020 at 13 h 06 min #15550
I’m using a UniformMass. I checked that face normals are all pointing outwards and then tried the scene with a really basic symmetric mesh (8 triangles on every face of the cube) which I made in gmsh and found the same issue.
Then I opened the turtorial in the SoftRobotics Component for the Pneumatic Gripper in order to check if the system in the turtorial would face the same issue and it did.
And because I was having the issue for my meshes even when I built them up symmetrically and then found the meshed in the turtorial yield similar behavior I got to think it may be more then a mesh issue.
Maybe there is an alternative method to build up the pneumatic actuator? Or is there a way in which I can figure out what the issue is?
Here are my files. With a little bit more fine mesh then the one previously discuused.A well as that I placed the cube on a surface.
Thank you for your support.30 March 2020 at 17 h 01 min #15584
I relooked at it, and am thinking it may indeed be an issue with the VTK, file.. Do you you have any recommendations for ensuring that one is right. As this changes the situation upon rotation whilst when rotating the stl of the cavity it behaves in the same way as before. I made it in gmsh are there specific things to watch out for besides the coarseness and the normals of the mesh. Thanks for your help and support! Hope you are doing well in the midst of these strange times.
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