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Cannnot get joint torque while setting velocity command for joints

asked 2014-09-03 23:38:46 -0600

murooka gravatar image

updated 2014-09-03 23:41:01 -0600

I use following plugin for controlling joints.

I'm sending velocity command to joint by SetVelocity function, and trying to get joint torque by GetForce function, but return value of GetForce is always zero.

When I send torque command by SetForce function, I can get correct joint torque by GetForce.

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I posted the question referred above, but hasn't received a response yet. Has anyone found a way around this problem?

Daniel L gravatar imageDaniel L ( 2015-01-19 13:52:06 -0600 )edit

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answered 2015-01-20 18:03:54 -0600

hsu gravatar image

updated 2015-01-20 18:25:24 -0600

SetVelocity bypasses physics (see the call to SetVelocityMaximal underneath), so forces were not computed based on target velocity. To do this in a physically realistic fashion, write a force based PID controller that takes velocity target as feedback, and GetForceTorque should give you more physically meaningful readings.

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When I tested SetVelocity() with DefaultRobotSim, if you sent a command to a joint from Gazebo's Joints pane, non-zero force values would start being returned from there on for that particular joint, even if you stopped using the pane and started a ros_control controller. Why is this the case? My original question is here:

Daniel L gravatar imageDaniel L ( 2015-01-24 17:10:52 -0600 )edit

GetForceTorque works well. Thank you!

murooka gravatar imagemurooka ( 2015-06-22 03:21:45 -0600 )edit

answered 2015-01-20 14:07:54 -0600

nkoenig gravatar image

Can you try using Joint::GetForceTorque?

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Thank you. It worked.

murooka gravatar imagemurooka ( 2015-06-22 03:22:48 -0600 )edit

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Asked: 2014-09-03 23:38:46 -0600

Seen: 3,486 times

Last updated: Jan 20 '15