Strange behavior of random mesh object on collision with mico gripper

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nehagarg
Posts: 17
Joined: 06 Mar 2015, 10:54

Strange behavior of random mesh object on collision with mico gripper

Post by nehagarg » 09 Nov 2017, 12:07

Hello

I want to collect some data for grasping objects by placing mico gripper at various positions w.r.t some object and doing some actions. When I do that, for some positions where gripper intersects the object, I get a very weird behaviour. Object does not fall down but gets attached to the gripper and gripper is able to also pick the object successfully. You can watch this in the video below:
https://drive.google.com/file/d/1rQjPY3 ... sp=sharing

The reason might be that my object is a random mesh object. This is not the case with pure shape cylinder object as can be seen in the video below:
https://drive.google.com/file/d/1hrH_ku ... sp=sharing

Is there a way to get the same behaviour from the random mesh i.e object falling down instead of sticking to gripper on collision/peircing? I tried using simCheckCollisionEx function to detect this. However that function detects collision even on a mild touch and number of segments can be equally large for a mild touch and for a total piercing through object.

I am also providing the link to my scene file for you:
https://drive.google.com/file/d/1rQL557 ... sp=sharing

You can move gripper by setting position of MicoTarget before starting simulation.

Thank You.
Regards,
Neha

coppelia
Site Admin
Posts: 6218
Joined: 14 Dec 2012, 00:25

Re: Strange behavior of random mesh object on collision with mico gripper

Post by coppelia » 09 Nov 2017, 17:34

Hello Neha,

if your dynamic objects initially interfere, then you will, most of the time, have an undefined behaviour. This is linked to the physics engine, but also to the fact that for collisions a penetration depth need to be computed, and this is very difficult for random shapes (which side of the random shape is inside, outside? In which direction should a force be applied if two shapes are initially overlapping? etc.)
The best option you have would be to slowly move to the grasping position, and make sure your collision pairs never approach a difficult situation (e.g. a small cuboid that completely encompasses a triangle from the random shape).

Cheers

nehagarg
Posts: 17
Joined: 06 Mar 2015, 10:54

Re: Strange behavior of random mesh object on collision with mico gripper

Post by nehagarg » 10 Nov 2017, 01:49

Hello,

Thanks for your reply. Avoiding such situations during data collection might be difficult for me.
Is there something I can do using simCheckCollision or simCheckCollisionEx to detect such cases?

Thank You.

Regards,
Neha

coppelia
Site Admin
Posts: 6218
Joined: 14 Dec 2012, 00:25

Re: Strange behavior of random mesh object on collision with mico gripper

Post by coppelia » 13 Nov 2017, 22:09

No, not really. The problem is not trivial and you want to look for a simple solution, not a complicated one (e.g. checking for collisions with the functions you mentioned).

Cheers

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