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wheels move by themselves

asked 2016-12-17 16:44:26 -0500

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So I made this simple two-wheel with a chassis robot in urdf. Then I ran it with roslaunch in gazebo, and found the wheels moving slowly by itself. I could see velocity and effort in axis1 of their joints set to -1. What's the problem here? Do you see the same behavior? or just my machine?

model.urdf: link alphbot.launch: link alphbot.world: link

EDIT: I'm using gazebo version 7.4.0 and ROS Kinetic and, (might not be relevant), running this in catkin workspace.

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answered 2016-12-19 10:39:55 -0500

chapulina gravatar image

One reason could be that your model starts the simulation inside the ground, so the first thing the simulation does is pushing it up strongly, and the robot might get some small velocity from that. Try spawning it in a higher position.

But in any case, to avoid drifting even further, you might need to configure surface properties a bit more, which is not trivial.

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I've tried spawning at z=0.1, 0.2, 1, 5, and 10 but it still behaved the same. I added <gazebo> tag with kp=10000, kd=1, mu1=50, mu2=30 to both wheels, and it went even faster! (I think it's because the wheels had more friction to grab and push the robot forward). By the way, the discrete integer "-1" really bothers me. So I tried changing velocity/effort limit and adding <transmission> tag (like example in http://wiki.ros.org/urdf/XML/Transmission). Yet it's still the same.

mixs222 gravatar imagemixs222 ( 2016-12-19 17:40:37 -0500 )edit
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answered 2017-04-11 10:01:27 -0500

eugene-katsevman gravatar image

Have you tried setting static joint friction for the wheel joints? This should stop them from responding to little torques coming from little calculation errors.

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Asked: 2016-12-17 16:44:26 -0500

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Last updated: Apr 11 '17