Strange problem with objects slipping out of place, what am I doing wrong?

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RobAtLab
Posts: 86
Joined: 10 Jan 2018, 17:49

Strange problem with objects slipping out of place, what am I doing wrong?

Post by RobAtLab »

I've been trying to simulate a robot with quite a lot of joints (all in force/torque mode) and plenty of compound convex shapes (all dynamic and respondable except a few which are static+non-respondable and used as visual covers for the blockier dynamic/respondable shapes in hidden layers). Right now I having an issue that parts seem to be slipping out of place when subjected to large forces. My model follows a hierarchy with a base mesh (pure shape, dynamic, respondable), that has a force sensor as child, another mesh (convex compound, dynamic, respondable) as child of that, then a load of joints (revolute,torque/force mode, motors enabled, some with target velocities others acting like servos with target positions and position control mode with default settings)some as child to it. Some of the joints have another mesh (compound convex, dynamic, respondable). Right now I'm finding that in some circumstances it seems that the dynamic+respondable shapes which are children of these joints sometimes slip out of place, I can't tell how.

Related to this, I think, is a problem I'm having when a joint on one robot is used to lift another robot up. This joint operates fine alone when the other robot hasn't been joined on to be lifted, but when the robot being lifted is added it stop working. The issue cannot be the torque, I kept setting it higher and higher on the lifting revolute joint (think a joint with a beam coming out of it and the other robot connecting to the end of the beam and being lifted up and over when the revolute joint turns 90 degrees) but still got no motion. Yet one thing that did happen when I tried all this was that one of the meshes, other than the beam, which was also a child of another revolute joint (this joint itself a child of the joint doing the lifting) slipped out of place relative to the joint it was supposed to be fixed relative to. I've tried increasing the maximum torque setting on the hinge, it doesn't lift. I've ensured that no objects are colliding when the hinge operates, and I've verified that it works when a robot isn't attached to the end of it.

I'm really new to V-REP, can you advise where I might look and which settings to fiddle with to try to fix these two issues, which I strongly suspect are related.

Thanks

coppelia
Site Admin
Posts: 8206
Joined: 14 Dec 2012, 00:25

Re: Strange problem with objects slipping out of place, what am I doing wrong?

Post by coppelia »

Hello,

it is very difficult to imagine what could be going wrong and what you are trying to achieve, without seeing the scene you are working on. Best is to prepare a minimalistic scene that illustrates your problem, then we can have a look at it. Also, did you try to switch to a different physics engine and see if that make a difference (improvement)?

Cheers

RobAtLab
Posts: 86
Joined: 10 Jan 2018, 17:49

Re: Strange problem with objects slipping out of place, what am I doing wrong?

Post by RobAtLab »

I've realised that most of my parts are really tiny, and very low mass, as the real robot parts are. I'm going to have a go at changing the internal scaling, perhaps using full scaling, of the physics engine. If that fails I'll try just making up some fictionally high masses and seeing if that improves things, I can probably do most of my simulation work without the true masses mattering. If it still doesn't work I'll post a simplified version here and see if anyone can help by looking at it.

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