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[DPRG] Please speak to me about SR518/Dynamixel servo deadzone/deadband, why I'd want it, and what to do with it

Subject: [DPRG] Please speak to me about SR518/Dynamixel servo deadzone/deadband, why I'd want it, and what to do with it
From: Paul Bouchier bouchier at classicnet.net
Date: Sun Jul 21 12:01:47 CDT 2013

Hi David. 
 
I would think a small amount of deadzone would be desirable in many
applications to conserve power & wear. It doesn't seem it should be
large, but it should be non-zero, otherwise the servo will "hunt" around
the desired setpoint & may never settle, OR the slightest
disturbance/flexure of the mechanical parts may kick it off into
re-seeking to the target location. If the target location is typically
in one spot (e.g. straight ahead for steering), this will tend to wear
the gears in one spot, and will consume more power than is necessary,
which is an issue for battery-operated machines.
 
I suspect the reason for this feature that's not seen on typical hobby
servos is that dynamixels have much higher accuracy, so would be more
prone to this kind of issue. Regular servos may have a fixed deadzone -
I don't know. Copied the list in case anyone else has more informed
comment.
 
Paul
 
-----Original Message-----
From: David Ackley [mailto:dackley at verizon.net] 
Sent: Thursday, July 18, 2013 9:12 PM
To: Paul Bouchier
Subject: Please speak to me about SR518/Dynamixel servo
deadzone/deadband, why I'd want it, and what to do with it
 
Hi Paul
 
I'm finally starting to dig into the details of the SR518/Dynamixel
servos and discovered that they seem to have a large
programmable/non-zero deadzone/deadband. To me, this programmable
deadzone/deadband appears to be functionally similar to gear backlash
which one tries to avoid and it seems to be something that would make
smooth/accurate motion control almost impossible. What is it for, why
would I want to have it, and how do I get
smooth/accurate/non-oscillating motion control with a servo that has a
deadzone/deadband?
 
I'm confused - but then I guess that I get more easily confused these
days =|;-{
 
Thanks
 
Dave
 
 
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