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NEMA17 stepper motor guesses?

Posted by Cougar281 
NEMA17 stepper motor guesses?
April 20, 2021 09:13PM
I just upgraded my X & Y steppers from 42HD4027-01 1.8* steppers to 17HM19-2004S units, and I'm considering doing the same for my extruders, but the problem is I have zero clue what they are, what their specs are, etc. The 42HD4027-01's are 1.8* units, with 400mN.m (0.40 Nm, if I'm not mistaken) holding torque, and the 17HM19-2004S's are 0.9* units with .46Nm holding torque. All of my original steppers came with my kit, which was a CBot Prusa i3 clone. While the motors for the X & Y axis had part number labels, the extruder motors are completely unmarked. The extruder motors are pretty much the exact same size as the new 17HM19 motors, while the old 42HD4027's are slightly shorter (attached image: stepper motor and old X/Y axis motor). That being the case, I'd suspect that the extruder motors are capable of more torque than the original X/Y motors.

Does anyone have any 'educated guesses' as to what the extruder motors might be (holding torque, etc), or, given the specs of the original X/Y motors and their size relative to the extruder motors, if some 17HM19's would even be up to the task (torque-wise)? It does seem to me that, based on the known torque ratings compared to the sizes of the motors in question, the extruder motors probably are in about the same torque range as the new 17HM19's, but that's just a guess. From what I've gathered, 0.9* motors are an upgrade over 1.8* motors all around, so if the 17HM19's might not be up to the task, any recommendations for a 0.9* stepper that would be up for extruder duty?
open | download - Steppers.jpg (94.6 KB)
Re: NEMA17 stepper motor guesses?
April 21, 2021 08:10PM
Not convinced it's a good idea.

Increasing the resolution comes at a cost - the controller has to send twice as many pulses to achieve the same distance.

With a retract, the extruder does high acceleration moves in both directions. If that exceeds the capability of the controller and driver combined, you miss steps unless you have a "smart" driver with feedback.

Further, unless you are capable of faster print speeds (unlikely) you don't get any benefit. I have seen people degrading their step multipliers to increase torque, but there's not a lot of point going the other way, the increased resolution isn't really needed on the extruder AFAIK.

Perhaps if you upgraded the system to 24V (driver and controller too) it might be worth it, but just upgrading the extruder motor on its own feels a very marginal improvement if any to me.

Edited 1 time(s). Last edit at 04/21/2021 08:15PM by DragonFire.
Re: NEMA17 stepper motor guesses?
April 22, 2021 06:57AM
It looks like you have an un-geared extruder. Your extruder steps/mm is probably low, maybe 100. If that's the case, upgrading the extruder motor to 0.9deg may give you more even extrusion. However, un-geared extruders need to use motors with lots of torque; and 0.9deg motors usually have somewhat lower torque than similarly-sized 1.8deg motors. My preference is to use an extruder with about 3:1 gearing instead. There are also some newer extruder designs with higher gearing and low-inertia motors, such as the Orbiter.

Upgrading axis motors from 1.8 to 0.9deg is typically worth it on a SCARA machine, just about worth it on a delta provided you use 24V power, but unlikely to make any difference on a Cartesian or CoreXY machine; except that mid-band resonance will occur at a different speed, so it may make the machine quieter or noisier.

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].
Re: NEMA17 stepper motor guesses?
April 23, 2021 06:53PM
Thanks for the feedback. I upgraded my printer to 24V some time back when the stock, over worked 12V power supply let the magic smoke out. Upgrading it to 24V was definitely worth it, and since then I've also upgraded it to a 120V SSR controlled silicone bed heater. So far, the 0.9* steppers seem to be doing well on the X/Y axis.

DC42, yes, the extruder is set to 94.4 steps/mm. I'll have to look into the options you mentioned. I would imagine a geared extruder would be better than the un-geared extruders that I have.

Edited 1 time(s). Last edit at 04/23/2021 06:54PM by Cougar281.
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