Servo Tuning detailed How To.

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06 Mar 2021 16:51 #201198 by Gene1934
In this thread, are the terms torque mode and position mode interchangeable?

I'm having tuning trouble with a quadrature encoder on the motor, and 2 stages of worm drive, mounted on the side of a BS-1 clone.
And what appears to be both high friction due to motor brushes, and possibly high drag in the BS-1 worm engagement although that seems to be wearing in. The clone, on inspection. has not a real contoured bull gear or a good worm so the fit isn't exactly perfect and will wear in if I crank in a little drag to kill backlash.

Worm gear ratio in the motor was unk, so the overall was measured by recording encoder counts, running it 100 turns using the home switch to count turns, and dividing the subtraction result by 360*100=666.66666667 for a SERVO_SCALE per degree in the ini file.

Everything else is volatile at this point.

Should I be tuning P-I-D or FF# for a position servo?
And since I seem to be running in degree's but a full turn of the BS-1 is 360 degrees, whats a ballpark pid_a.FF0 value as that does not seem to have much effect here.

Thanks all.

Cheers, gene

Cheers, Gene Heskett
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"There are four boxes to be used in defense of liberty:
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07 Mar 2021 01:52 #201252 by andypugh

Gene1934 wrote: In this thread, are the terms torque mode and position mode interchangeable?


Not at all. They are opposite ends of the scale.

torque mode -> velocity mode -> position mode.

In torque mode the command from LinuxCNC is motor current.
In velocity mode it is a velocity command to the drive.
In position mode it is a position command to the drive.

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07 Mar 2021 12:27 #201284 by Gene1934
ok, then describe exactly what defines these differences in the hal hookups. In my searches for example configs related to servo tuning, none describe the hal hookups to define the diffs.

Position mode is my target.

Thanks Andy.

Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page < geneslinuxbox.net:6309/gene >

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07 Mar 2021 18:55 #201325 by andypugh

Gene1934 wrote: ok, then describe exactly what defines these differences in the hal hookups.


The HAL is exactly the same. Encoder position comes in, numbers go out.
All that changes is what the numbers going out represent.

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07 Mar 2021 21:44 #201368 by Gene1934
That also seems to be suspect, so I am re-running the code that calculates the scale from the passage of 100 revs according to the home switch. As its a bunch slower than your harmonic drive, it will take about an hour to do 100 turns.

Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page < geneslinuxbox.net:6309/gene >

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