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COLLADA Mesh vs Box behavior difference

asked 2013-04-14 08:19:34 -0500

jys gravatar image

updated 2013-04-16 12:43:40 -0500

I am currently using Fuerte-Gazebo (Gazebo-1.0.2).

Given same exact values under <collision> <surface>. (literally all values are same including size) 1. simple box collada mesh 2. box from gazebo UI

They behave differently when I put a bowl/can on it. On collada model, it sort of bounces and jumps out. (even though all collision values are same) But on a same size box, objects will soon settle down.

What is causing behavior difference? Is there anything other than <collision> <surface> that plays the role?

Here are the values I copied from box generated from Gazebo client.

      <surface>
        <friction>
          <ode mu='2147483647.0' mu2='2147483647.0' fdir1='0.0 0.0 0.0' slip1='0.0' slip2='0.0'/>
        </friction>
        <bounce restitution_coefficient='0.0' threshold='1000000.0'/>
        <contact>
          <ode soft_cfm='0.0' soft_erp='0.20' kp='2147483647.0' kd='1.00' max_vel='5.00' min_depth='0.00'/>
        </contact>
      </surface>
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does your box collada mesh have a high polygon count? Not sure if it's the case but it could be that it's generating many contact collisions with the bowl/can which causes the unstable behavior. Of course it could be something else..

iche033 gravatar imageiche033 ( 2013-04-16 03:08:01 -0500 )edit

Not too familiar with collada mesh. it was exported from sketchup. It appears as flat box in sketchup. Actually, visualizing in meshlab shows only two polygons for the surface.

jys gravatar imagejys ( 2013-04-16 07:10:49 -0500 )edit

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answered 2013-04-16 23:38:02 -0500

scpeters gravatar image

The trimesh collision shapes currently use a different collision detection algorithm than the simple shapes (box, sphere, cylinder), which tends to cause different contact behavior. If you are able to build the latest version of gazebo from source (default branch), then you can try creating some objects with the collide_without_contact flag set and View Contacts enabled. The will allow you to see the location of contact points computed by the collision detection algorithm without generating contact forces. Here's an example world that has objects with the collide_without_contact flag. For observing the contact points, you may want to turn off gravity and View Transparent.

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That seems like lots of work. I need a workaround in Fuerte. Do you know if messing with number of polygons will affect the behavior? (as mentioned by @iche033 above in the comment?)

jys gravatar imagejys ( 2013-04-17 15:23:03 -0500 )edit

can you try changing the max vel to a small value like 0.01?

iche033 gravatar imageiche033 ( 2013-04-19 12:25:36 -0500 )edit
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Asked: 2013-04-14 08:19:34 -0500

Seen: 263 times

Last updated: Apr 16 '13