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# What are the SDF Damping Units?

Here's the description of SDF joint --> axis --> dynamics --> damping, "The physical velocity dependent viscous damping coefficient of the joint." Can you tell me what units this number is interpreted as having.

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## 4 Answers

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It is Neutons per (meter per second), i.e. N * s / m (force per velocity ) or N * m * s (torque per angular velocity) depending on joint type.

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Whence did this info come?

( 2018-05-10 09:49:48 -0600 )edit

http://gazebosim.org/tutorials/?tut=ros_urdf#Joints, "the dynamics element with a viscous damping coefficient of 0.7 N*m*s/rad".

( 2018-06-13 02:04:54 -0600 )edit

Hi

There should be no unit I think, since we should have something like energy_loss = damping * joint_velocity. I did not run any test, but one could run a simulation with two balls (one with damping, the other one without) fixed to the ground by prismatic joints and log information about velocity.

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As it said, it is a coefficient. So it has NO units.

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## Comments

Please do not confuse joint->axis->dynamics -> damping (which has the same units as in URDF's joints, i e. force/velocity ratio or toque/angular velocity ratio depending on joint type) with velocity_decay , which are pure unit-less scalars indeed.

( 2017-04-21 09:51:43 -0600 )edit

If it's related to velocity_decay, it's the fraction of velocity reduced per time step. At 1000 time steps per second, a decay of 0.01 is quite strong.

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Asked: 2016-03-07 21:49:35 -0600

Seen: 1,693 times

Last updated: Apr 21 '17