PR2 drifts over time in Gazebo

asked 2012-08-22 04:05:18 -0500

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This is more a curiosity than an actual problem.

Yesterday morning, I started gazebo, and it ran smoothly throughout my work day (which is great, first time that happened). When I left, I forgot to turn of my workstation, and when I got back this morning, the PR2 had moved a little. Looking back, I remember noticing this towards the end of the day yesterday (simulation time approx 9-10 hours) as well, but didn't pay much attention to it.

What is the reason for this? I haven't used a single node that has anything to do with the base.

Attached is a screenshot of the current Gazebo state. The robot is supposed to be in front of the middle of the table (where the coke cans are).

answered 2012-08-22 05:16:55 -0500

Nan Jiang
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Yes that happens. I guess you have let the robot interact with the table and object, where the counter force gives the robot a very very small (but not 0!) speed. The dynamics simulated in Gazebo is not that perfect so the robot probably never stops.

By the way, this is also part of the reasons that I post this question.

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The other thing I notice is that the table hardly moves... so maybe pr2 drifts away because it has wheels under the torso. Maybe it is possible to remove the wheels if you just want it to stay in a fixed position... I don't know. I am also curious about the solution to this problem.

Nan Jiang ( 2012-08-22 05:19:27 -0500 )edit

I think it is indeed infinitesimal reaction forces that causes this, it's a common problem in explicit simulation. Worth noting if you're running a long simulation where the robot is supposed to be fixed at all times.