vibration with Bullet 2.8

[martin]

Hello Coppelia,

I am working with ubuntu 18 and the CoppeliaSim 4.5.1 rev 2.

In this case, I came back with another issue, in this case, regarding the Bullet 2.8 physics engine. In the following scene, I get some "vibratory behavior" in the robot when the simulation starts:
https://www.dropbox.com/s/q1qlhqqf0zenc ... 0.ttt?dl=0

I add a video, recorded with the "video recorded" Tool, in the case that you could not see it.
https://www.dropbox.com/s/93df3sd3zoskc ... t.avi?dl=0

As far as I know, in oldest version of the simulator, this was solved increasing the inertia of the shapes that constitutes the robot. However, as in the current version that aspect has changed quite a bit (now, there is an uniform density parameter for each shape and from this the mass and inertia matrix of the shape are obtained) how it is the suitable form of solving such strange behavior? Is it related with some parameter of the bullet simulator?

Regards!

[coppelia]

In general, engines haven't changed much between CoppeliaSim V4.4 and V4..5, except for the switch to double floating point precision. The mass and inertia dialog, i.e. the shape dynamics dialog) however has been reworked quite a bit. For instance, the mass/inertia scaling is now done via [Menu bar --> Edit --> Shape mass and inertia --> scale ...].

So for your robot, scaling the inertia by 5x for the leg shapes would improve the situation quite a lot for the Bullet engine. And for the MuJoCo engine, set the armature parameter to 2 for all the joints, and the robot won't jump anymore

Cheers