Real-Time Physics Simulation Forum

Posted: **Fri Dec 25, 2020 6:26 pm**

Hi all,
first of all Merry Xmas!

I am new to pybullet and want to perform a collision detection self contact and contact with several closed loop systems installed next to each other.The geometry is created in Creo and exported as obj files.

I read now tons of sites and have several questions:

1. I came to the conclusion, that the urdf file import in not possible for closed loop systems. Is that correct?
2. Because of 1, I have generated a .py file where I define a CollisionShape for each component like shown below

Code: Select all

                 p0 = p.createCollisionShape(p.GEOM_MESH,
							   halfExtents=[0, 0, 0],
							   fileName="obj/part0.obj",
							   collisionFramePosition=shift0,
							   meshScale=meshScale)

I assembled the individual shapes to

Code: Select all

    mla = p.createMultiBody(body_Mass,p0,visualShapeId,basePosition,baseOrientation,
                        linkMasses=link_Masses,
                        linkCollisionShapeIndices=linkCollisionShapeIndices,
                        linkVisualShapeIndices=linkVisualShapeIndices,
                        linkPositions=linkPositions,
                        linkOrientations=linkOrientations,
                        linkInertialFramePositions=linkInertialFramePositions,
                        linkInertialFrameOrientations=linkInertialFrameOrientations,
                        linkParentIndices=indices,
                        linkJointTypes=jointTypes,
                        linkJointAxis=axis)

Is there a way to define and pin a base part, similar to the import option "useFixedBase" for urdf import? If not, how can I specify which part should be the base and how can I fix it?

3. If I use pybullet headles, how can I detect collisions / get an output somewhere, e.g. textfile

Thanks in advance for your help

Posted: **Sat Feb 20, 2021 9:08 am**

Problem partially solved.
closed loop is not possible for urdf, but creating a constraint after importing the urdf works.

Posted: **Mon May 02, 2022 8:06 pm**

This is very late, but I think changing the mass to be 0 of any link is equal to making it fixed? specifically for fixing a base or setting something as a base I think you need to make it the base link so that the urdf importer knows.
Btw thank you! Your answer is very helpful to me! I'm also trying to simulate something potentially with a closed loop and was wondering how that could be done in either createMultiBody() or urdf.

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