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What are the SDF Damping Units?

asked 2016-03-07 21:49:35 -0500

raequin gravatar image

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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answered 2017-04-20 05:16:16 -0500

eugene-katsevman gravatar image

updated 2017-04-21 09:53:33 -0500

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?

raequin gravatar imageraequin ( 2018-05-10 09:49:48 -0500 )edit

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

jwchang gravatar imagejwchang ( 2018-06-13 02:04:54 -0500 )edit

answered 2016-03-10 06:01:16 -0500

debz gravatar image


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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answered 2017-04-21 08:50:50 -0500

winston gravatar image

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

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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.

eugene-katsevman gravatar imageeugene-katsevman ( 2017-04-21 09:51:43 -0500 )edit

answered 2017-09-27 12:55:22 -0500

clydemcqueen gravatar image

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 -0500

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Last updated: Apr 21 '17