Help choosing a more appropriate stepper
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Hello all,
Could I please trouble you for assistance choosing a better stepper motor for my extruder. Please forgive the wall of text; trying to include everything I've tested and learnt.
I've tried several motors below, and they all work well enough, but they have limitations.
My extrusion speed becomes limited (I believe) by hitting the speed limit of the steppers - a factor of using the remote direct extruder with 40:1 reduction. What I observe is that I can print reasonably fast, but during especially quick accel/jerk moves, the motors stall.
They stall @ the motor, there is no filament grinding, there is no nozzle blockage or other impedance to torque. (This is backed up by the fact that I can remove the load (just disconnect the flexible shaft), and if I run the same tests, it stalls at exact same points.)
During testing/printing, I primarily have to greatly limit the jerk setting to the point that it slows down the entire print. It's definitely jerk that is the limiting factor, not general accel, max speed, current, or anything else I can find.
If I increase the jerk, sections of a model that print fast, but with low jerk, print well, but parts where there is high jerk the motor stalls and there's no extrusion. During on the fly adjustment, there is huge changes to overall print speed as I increase the jerk.
Jerk: limited (in actual real use) to 40mm/min (even at this value, it still occasionally stalls, but it's already slowing prints down a lot). I can print reasonably reliably with this value. Any higher and it'll stall as described. Jerk Policy (love the phrasing) is set to 1.
Extruder acceleration: I've found I can set to anything, doesn't matter if 200, 2000, 20000... 2,000,000 (I've literally set it to 2 million) it doesn't cause the extruder to stall, or have any noticeable effect at all - I assume that the jerk is the limiting factor before accel comes into play?
Max speed: same as accel, I can set to anything (again, I tried 2 mil)
Current; I use as max ~80% of rated as standard, but I've also tried lowering the current of all 3 steppers I've tried, and it had no significant improvement. I even tried increasing to overcurrent just to try, nil effect.HW; Duet 3 6HC @ 24V, flex3drive G5 extruder (40:1 reduction)
Motors I've tried:
SparkFun ROB-10846 https://www.digikey.com.au/en/products/detail/sparkfun-electronics/ROB-10846/5318748 (0.9°, torque 68oz-in, inductance reportedly 2.88mH, current 1.7A, rotor inertia unknown)
E3D MT-1701HSM140AE (0.9°, torque 18oz-in, inductance 2.0, current 1.4A, rotor inertia 30g.cm2)
E3D MT-1703HSM168RE (0.9°, torque 48oz-in, inductance 3.6, current 1.68A, rotor inertia 54gcm2)
https://wiki.e3d-online.com/images/c/c4/Motor-Datasheet-All.pdfWhat I've learnt looking at:
https://flex3drive.com/support/assembly/motors/
https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors
https://duet3d.dozuki.com/Wiki/Choosing_an_extruder_driveSo, what I understand from above...
... Things that should improve speed:
use 24V - already am
Lower the current (to reduce back EMF and will have limited benefit) - tried this, didn't make much difference
Does micro-stepping affect speed?... Qualities to look for in a stepper motor:
1.8° over 0.9°
low inductance - Duet states generally aim <4mH, flex3drive say "ideally... below 10mH"
low rotor inertia - don't know what constitutes a "low" value though?
rated torque - don't know???
rated current - don't know???I currently haven't tried a 1.8° stepper (well, I did try a super cheap knockoff type motor, but I have absolutely no specs on it, so I'm ignoring it)
I know that I'm going to need a 1.8° stepper, but I don't really know what constitutes a "low" inductance, or a "low" rotor inertia, and I don't really know what sort of torque or current rating I should look for, since they don't really seem to affect speed? Well, torque drops off as speed increases, so I assume you still need a decent amount of torque, because at the higher speeds I'm after, the torque will be significantly reduced...
Is the change from 0.9 to 1.8° going to have such a big effect on what I'm trying to achieve that I'm overthinking the other specs?
This is a list of digikey's bipolar 1.8° steppers https://www.digikey.com.au/en/products/filter/stepper-motors/179?s=N4IgjCBcoGwOwFYqgMZQGYEMA2BnApgDQgD2UA2iAMxgCcc9IAusQA4AuUIAyuwE4BLAHYBzEAF9iAJhkAWZCDSQseIqQogpABi3M2nSCAAiJAK4AjbPgnEAtFIVL%2BptWUiUkTcZJAwFAgBMuWzAtCH0uEGJ2AE9Wa0NMXDRvIA
I know I need to try a 1.8°, but if I'm going to buy one, I might as well optimise other specs too. If someone could recommend a stepper or what to look for (or some other way to improve performance), I would be very grateful!
Many thanks,
Jon -
@jhalewood said in Help choosing a more appropriate stepper:
My extrusion speed becomes limited (I believe) by hitting the speed limit of the steppers
If you already have problems with extrusion speed, how about retraction? Do you retract at the same speed as you print?
The digikey listing isn't very helpful. I could reduce the number of candidates to '60', by selecting 5mm shaft. I guess, that's what the Nimble needs?
Looking further for lowest rated voltage only the trinamic steppers popped up. They are quite expensive and their voltage rating isn't very low.
I'd recommend looking for other vendors and pick a Nema17 pancake motor with low inductance. Speed is all you need with 40:1 gear ratio
