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Gazebo and transmissions: mechanicalReduction and motorTorqueConstant

asked 2012-02-13 02:57:41 -0600

Georg gravatar image


could anybody explain the role and effect of the transmission parameters mechanicalReduction and/or motorTorqueConstant when using a SimpleTransmission in Gazebo?

While I do understand the words, I did not really find a lot of documentation on how they actually influence simulated joints.



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answered 2012-02-13 09:10:42 -0600

sglaser gravatar image

The transmissions transform state from actuator space to joint space (and efforts from joint space to actuator space). The robot is simulated in joint space, so in simulation, the efforts are immediately transformed back into joint space (and the state is first transformed from joint space), as shown in this diagram.

In simulation, the mechanicalReduction and motorTorqueConstant are immediately applied and unapplied, so changing them will have no effect on the simulation. They only change the reported values of the actuators.

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Thanks a lot for this comprehensive answer. If I use one of the predefined controllers, e.g. robot_mechanism_controllers/JointPositionController, on which side of the transmission would it apply its effort?

Georg gravatar image Georg  ( 2012-02-13 20:39:08 -0600 )edit

The controllers apply effort to the joints.

sglaser gravatar image sglaser  ( 2012-02-14 13:07:11 -0600 )edit

So the idea behind this, is that there is some interface to the actuator so that actually the effort on the joint side is controlled and not the effort on the actuator side of the transmission? I assume this is, how the PR2 is built...

Georg gravatar image Georg  ( 2012-02-15 00:43:40 -0600 )edit

The controller commands effort on the the joint, and the transmission translates them into effort on the actuator.

sglaser gravatar image sglaser  ( 2012-02-15 09:38:13 -0600 )edit

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Asked: 2012-02-13 02:57:41 -0600

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Last updated: Feb 13 '12