CoppeliaSim forums

Posted: **24 Jan 2024, 09:23**

There is a serial 7-DOF space manipulator, which is in the zero-gravity environment. How can I keep the base orientation constant and the base position follow the law of conservation of linear momentum?

Remark:

1. When joints move according to the instructions I give, obviously the base position will change to ensure that the total centroid position of the system remains unchanged (assuming the system is not subjected to external forces). I have derived the dynamic model of the system, my purpose is to verify whether my dynamic model is correct through the physics engine of coppeliasim.
2. Actually the orientation of the base should be controlled by the jet device, but it seems difficult, so I don't consider this method. Can I directly constrain the base orientation, it looks simpler and more precise.

I'm really looking forward to someone helping!

Posted: **24 Jan 2024, 16:25**

Hello,

I think you have several approaches you can use. 3 that I can think of:

set the dynamics properties of the base object to have a very large inertia. Best engines to use in that case: MuJoCo, Newton (or Vortex). ODE and Bullet won't perform well I guess in that situation
set the dynamics engine properties of the base object to have a very large angular damping
use 3 prismatic joints that are free, i.e. not controlled. Best would be to use MuJoCo here too, since you do not need to add auxiliary masses in-between as with other engines:

Code: Select all

-- MuJoCo:
fixedBase --> prismaticJoint1 --> prismaticJoint2 --> prismaticJoint3 --> robotBase -->

-- Other engines:
fixedBase --> prismaticJoint1 --> auxMass1 --> prismaticJoint2 --> auxMass2 --> prismaticJoint3 --> robotBase -->

With the auxiliary masses, there will be some influence on the rest of the robot.

Cheers

Posted: **25 Jan 2024, 06:31**

Thank you very much! I will try your method.

Posted: **27 Jan 2024, 13:48**

The problem has been solved. I use the "SetObjectOrientation" function at every step.

CoppeliaSim forums

Constrains only orientation but not position

Constrains only orientation but not position

Re: Constrains only orientation but not position

Re: Constrains only orientation but not position

Re: Constrains only orientation but not position