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6-lead steppers: lower current = more torque?confused smiley

Posted by o_lampe 
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o_lampe
6-lead steppers: lower current = more torque?confused smiley
June 08, 2017 07:14AM
I found these steppers and want to know if it's a typo or real?



I can only imagine their max. speed is much lower then?
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george4657
Re: 6-lead steppers: lower current = more torque?confused smiley
June 08, 2017 09:14AM
Numbers look reasonable.
Wiring 1 is using full coil so it would have twice the inductance of using split coil.
As a result the speed would be reduced. This is the same as wiring an 8 wire motor in series.
Wiring 2 uses only half of the coil so it would run faster but have lower low end torque.

It is best to get an 8 wire motors as you then use both coils in parallel.

George
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o_lampe
Re: 6-lead steppers: lower current = more torque?confused smiley
June 08, 2017 09:43AM
OK, got it.
It's like a star/delta config on a 3-phase motor.
Makes me wonder if it would make sense to make it switchable?
Star config for hard work.
Delta for travel moves.
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o_lampe
Re: 6-lead steppers: lower current = more torque?confused smiley
June 22, 2017 01:26PM
It seems, the inductance in full torque config ( 2.1A/1.9Nm ) is to high for 24V. The torque drops pretty fast at higher RPM .
I made some travel speed tests and with a pulley gear ratio of 3:1 max travel speed was ~200mm/min ( 6400 steps/mm )
Then I changed gear ratio to 1:1 ( 2133.33 steps/mm ) and got +400mm/min travel.

I'll try the 3A/1.35Nm config with 3:1 gear ratio tomorrow. IMHO this will be the best compromise...
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dc42
Re: 6-lead steppers: lower current = more torque?confused smiley
June 23, 2017 04:47AM
If this specification is correct:



then, relating it to the data in your earlier post, the inductance is 1.6mH for half a phase so it will be 6.4mH for a full phase. You can work out the supply voltage you need to maintain torque up to a desired target speed, see [duet3d.com].

Edited 1 time(s). Last edit at 06/23/2017 04:48AM by dc42.


Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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o_lampe
Re: 6-lead steppers: lower current = more torque?confused smiley
June 23, 2017 10:33AM
Thanks David for the link.
It seems our datas are mixed up...holding torque in 3A-config should be 1.35Nm or do they run the stepper at 3A with full phase?
I'll do the math with your formulas, although they are for "no load" scenarios. But it's save to use 50% of the calculated max. speed as this is the typical point where torque descends.
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dc42
Re: 6-lead steppers: lower current = more torque?confused smiley
June 23, 2017 11:13AM
Actually the calcs work out better for loaded scenarios, because the back emf due to rotation then lags the back emf due to inductance, reducing the total drive voltage needed. So you can take the no-load scenario as the worst case.


Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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o_lampe
Re: 6-lead steppers: lower current = more torque?confused smiley
June 23, 2017 11:55AM
Yes, that explains why I got lower rev/s values at higher motor current ( read required current )

I revers calculated max. rev/s at 24V and got
~4 rev/s for the 6.4mH@2A_1.9Nm wiring *
~7.3rev/s for the [email protected]_1.35Nm

* In fact I could run the stepper almost twice as fast as 4 rev/s. How is that possible?
edit: Does your formulas fit for yerk movement, but accelerated moves reach higher speed?

Edited 1 time(s). Last edit at 06/23/2017 12:02PM by o_lampe.
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dc42
Re: 6-lead steppers: lower current = more torque?confused smiley
June 23, 2017 04:17PM
My formula estimates the voltage you need to maintain full torque at a given speed. But motors in 3D printers generally produce much more torque than you need to produce motion. The greater the excess torque, the more accurate the positioning is.


Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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o_lampe
Re: 6-lead steppers: lower current = more torque?confused smiley
June 25, 2017 01:53PM
Finally tested the other wiring option ( 1.6mH ) and it made all the difference. I could run the M10 leadscrew at 600mm/min which is 4 times faster than before. ( although I turned the current down to 2.4A )
It's the best setting for 24V and a pulley gear ratio of 3:1

Edited 1 time(s). Last edit at 06/25/2017 01:53PM by o_lampe.
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