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force torque sensor and control force values

asked 2017-08-16 11:56:36 -0500

RamilK gravatar image

Hi all, I'm using plugin to find torques in joints and control joints using gazebo_ros_control plugin. However when I compare joint torque from sensor and position_controller/state/command value (result of PID work), they are not the same. Their behaviour looks similar but as if sensor value n times smaller than command value. What could be the reason? Thanks!

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units? proportional term?

2ROS0 gravatar image 2ROS0  ( 2017-08-16 12:20:18 -0500 )edit

Sensor uses GetForceTorque function of gazebo which provides values in SI as I expect. ros_control generates effort as I understand and should be also in N*m. There are no multiplication factors

RamilK gravatar image RamilK  ( 2017-08-16 12:56:55 -0500 )edit

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answered 2017-08-17 06:20:57 -0500

RamilK gravatar image

Hi everyone! Seems that the solution is found! The issue was that i set high friction and damping coefficients in joint. As mentioned in here, motor torque = joint torque + friction (static and dynamic damping). PID set motor torque by Joint::SetForce in Gazebo and joint effort limits its value (see here). As for ft_sensor, it shows joint torque value (motor torque - friction). So if we set friction to 0 (both static and dynamic) ft_sensor and PID values are identical. Or in case of joint effort limits effect ft_sensor value is cut.

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Asked: 2017-08-16 11:56:36 -0500

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Last updated: Aug 17 '17