Degrading performance of 0.9° steppers

I've bought a batch of 42BYGHM810 steppers a while ago and I was pretty happy with their behavior.
But over a few working hours they seem to cause problems. It feels, like they've lost the permanent magnetism which causes missing steps. I even blamed my diamond hotend to be partially clogged, but now I think it's the steppers.

I have one unused stepper and compared it with the used ones:
When I shortcut black/green and red/blue coils and turn the shaft by hand, I can feel much more resistance with the new one.

Are you stepper inside a heated chamber?

What electronics and power supply voltage are you using? Missing steps after a period of use could indicate overheating stepper drivers. 0.9deg motors typically need 24V power unless you restrict them to low speeds.

Those motors are rated at 50C max ambient and 80C max temperature rise. So I think it's unlikely that you have overheated the magnets, unless you are using powerful external stepper drivers. If you turn the shafts with your fingers when the motors are not powered, can you still feel the detents?

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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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Dust
Are you stepper inside a heated chamber?

Only one stepper is in an enclosed printer, but it's not heated. That one was on 12V until it stopped extruding at all. The drivers ( and I tried RAPS, TMC2100, A4988 and DRV8825 ) don't have time to overheat. It skips from the start. I replaced it with a 1.8° ...1204 stepper ( 0.4A instead of max. 2.4A ) and it works flawless.

The other steppers were on 24V in my diamond_delta. The XYZ steppers are on top, so no risk of overheating from the heatbed either.

I can feel the detents when coils are open. The difference is with shorted coils.

... stepper magnetization degrades when heated above 80 degC -- with some cheapish motors this will start even at above 60 degC ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

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A motor current rating of 2.4A is way too high for any sort of plug-in driver.

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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].

Quote
dc42
A motor current rating of 2.4A is way too high for any sort of plug-in driver.

I thought I could run them with much lower current, since their torque rating is pretty high. 2A+ is no problem for RAPS128 drivers.
Now I'm hesitating buying 1.2 or 1.7A 0.9° steppers. Will they be good enough for extruder direct drive?

Edited 1 time(s). Last edit at 02/06/2017 06:23AM by o_lampe.

... I'm driving RAPS128 with max 1,7A -- you'll need "serious cooling" for higher currents - only forcing air won't be enough.

My NEMA23 steppers are rated with 2,2A, but happy with 1,7A too with speeds up to 400mm/s.

Changed to Nanotec 3A-drivers for tests with higher speeds (up to 800mm/s) - they stay cool at 2A "only"

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Quote
o_lampe

Quote
dc42
A motor current rating of 2.4A is way too high for any sort of plug-in driver.

I thought I could run them with much lower current, since their torque rating is pretty high. 2A+ is no problem for RAPS128 drivers.
Now I'm hesitating buying 1.2 or 1.7A 0.9° steppers. Will they be good enough for extruder direct drive?

The problem with using a high torque motor and running it at (say) 30% of maximum current on the grounds that you don't need more than 30% of the rated torque is that with high torque you also get high rotor inertia. So you need to use low acceleration and jerk so that the rotor inertia doesn't keep the motor position too far behind where it is wanted resulting in missed steps. Personally I always use at least 60% of the rated current, although I have known printers run at 50%. So perhaps I should have said "rather too high" instead of "way too high".

If I were using a direct drive (i.e. non-geared) extruder, I would choose a high torque motor and want to be sure of being able to run it at up to 85% of its rated current. So a 1.7A motor would be no problem for a Duet, but would be marginal with most plug-in drivers. I don't know the specifications of the RAPS128, but unlike most plug-in drivers the chip is designed to be cooled from the top, which means that a heatsink and fan can provide reasonable cooling.

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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].

If I had to choose between a 40mm and 48mm long 0.9° stepper, both rated 1.7A, I should choose the shorter one because of the lower inertia?

Quote
o_lampe
If I had to choose between a 40mm and 48mm long 0.9° stepper, both rated 1.7A, I should choose the shorter one because of the lower inertia?

No, if it's for an un-geared extruder, choose the longer one. The ratio of torque to rotor inertia is probably similar for both drives. OTOH you should choose a 40mm 1.7A motor over a 48mm 2.4A one if your drivers can't deliver 85% or so of 2.4A.

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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].