How to make my Shadow Hand not exploding?

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benjamin
Posts: 8
Joined: 12 Feb 2015, 11:50

How to make my Shadow Hand not exploding?

Post by benjamin » 12 Feb 2015, 12:14

Hello everyone,

I need to use the Shadow Robotics Hand (the one with biotacs) in V-REP so I converted the xacro model available in ROS to a URDF one, made some modifications in the file (file paths starting with package:// with absolute path) and then used the URDF import plugin in V-REP.

I have now the hand quite well imported in my scene, I removed the big spheres at the fingertips (don't know why they where here) and I started the simulation. But when I do that, the hand simply explode... I spent many hours trying to fix with behavior (acting on respondable properties, create new respondables, ...) but I couldn't come to a viable model.

I'm quite new to V-REP and since I can't find a solution myself so I give you the scene file I'm using. I hope someone can tell me how to fix this.

Thanks

https://www.dropbox.com/s/mnmpy32q7gacv ... l.ttt?dl=0

p.s : If I can come to a usable model of the shadow hand, I will be quite happy to make it public so that other users can enjoy it
Last edited by benjamin on 13 Feb 2015, 16:39, edited 2 times in total.

coppelia
Site Admin
Posts: 7335
Joined: 14 Dec 2012, 00:25

Re: How to make my Shadow Hand not exploding?

Post by coppelia » 13 Feb 2015, 08:40

Hello,

looking at your hand, it seems that the masses and moments of inertia are completely wrong.
Remember also that the inertia values that you specify in V-REP are all divided by the mass of the object (so basically massless values). But this is normally handled by the URDF importer.

Next, you have to be aware that the physics engines have a had time with masses and inertias that are too different. Make sure to carefully read this section, and specially design considerations 7 and 8.

Cheers

benjamin
Posts: 8
Joined: 12 Feb 2015, 11:50

Re: How to make my Shadow Hand not exploding?

Post by benjamin » 13 Feb 2015, 10:08

Thanks for your answer, I'll try to find real masses and moments of inertia of this hand and set them in the model to see what happens.

I'll keep you posted

benjamin
Posts: 8
Joined: 12 Feb 2015, 11:50

Re: How to make my Shadow Hand not exploding?

Post by benjamin » 13 Feb 2015, 13:47

Following your advice, I modified the inertia matrices and I have also modified the respondable masks to avoid conflicts between two consecutive and overlaping shapes and now I have a hand that's working quite well. I'll try to get in touch with Shadow Robotics to get the joint masses and inertia matrices and the maximum torque for each motor (1000N.m seems quite high for me). I attach my scene if anyone is interested.

https://www.dropbox.com/s/82eueo0xiw9m4 ... a.ttt?dl=0

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