HEBI Robotics
Damping coefficient and static friction constant #48
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Hi, I guess my reply to my previous post went unnoticed so I am asking it here in a new post. What is the difference between motor inertia and gear inertia @ motor? Which one needs to be used when you are just concerned about controlling the output torque? Also, I could not find the damping/viscous coefficients and static friction constants. Is it possible to provide these constants specifically for the X8-3? Thank you for your help.
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Replies: 4 comments
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Sorry for the delay getting back to you. Thanks for bumping this issue to a new topic! The motor inertia is the inertia of the internal brushless motor of the actuator. The gear inertia is the 'reflected inertia' of the various stages of the gear train. Both of these terms are expressed in the frame of the motor (before the gear reduction). We unfortunately don’t have a good estimate for viscous/static friction coefficients of the motor or the geartrain. In terms of what friction/inertia parameters are important for control, we generally have not found modeling the details of the motor/geartrain to be very useful for control, beyond knowledge of the motor's electrical resistance and torque/speed constants. This is because position/velocity/torque sensing on the actuators are based on encoders directly on the output, after the gear reduction. That said, if you're trying to identify these parameters, we'd be happy to help out with any questions about gathering / analyzing actuator data, or interpreting the results. Hope that helps,
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Thanks Dave, so can I assume that total inertia of the motor would be the sum of these two inertias?
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Yes.
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Ah ok, thanks. :)
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Sorry for the delay getting back to you. Thanks for bumping this issue to a new topic!
The motor inertia is the inertia of the internal brushless motor of the actuator. The gear inertia is the 'reflected inertia' of the various stages of the gear train. Both of these terms are expressed in the frame of the motor (before the gear reduction).
We unfortunately don’t have a good estimate for viscous/static friction coefficients of the motor or the geartrain.
In terms of what friction/inertia parameters are important for control, we generally have not found modeling the details of the motor/geartrain to be very useful for control, beyond knowledge of the motor's electrical resistance and torqu…