Confusion - Changing Stepper Motors

Confusion - Changing Stepper Motors

Postby JoshiTravels » 2016-May-Sun-08-May

Hi all,

Can anyone walk me through why 3d printers generally share the same stepper motors?

I understand holding torque is a big factor - but if I wanted to swap out motors to go for one with a longer shaft, or a shorter body would it be as simple as unplugging the 4-pin connector and plugging a new one in, or would there be driver/software changes too?

I know so little about the electronics side of things, id love to learn more.

Essentially I am thinking of taking part my old Simple Maker-edition and using all the bits to assemble my own printer with a custom build volume. Id like to use the current Y-stepper in the Z-position because it sits shorter/lower down. Can I just swap the connectors around and expect it to work the same, or have I got this wrong?

Thanks in advance!

Josh
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Confusion - Changing Stepper Motors

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Re: Confusion - Changing Stepper Motors

Postby RetireeJay » 2016-May-Sun-13-May

It turns out that there are quite a few specs to consider.
If you're re-using one of the existing motors, that simplifies things a bit. The wiring will be compatible with the Printrboard.
Standard steppers used in Printrbots are all 200 steps per revolution, and they are all NEMA-17 - which means that with the motor shaft facing you, the square is 1.7 inches across.

Next is the torque specification, and the deeper the motor the more torque it will be able to generate (that's pretty intuitive: bigger = stronger). So don't substitute a smaller motor for a bigger one unless you have a pretty good idea about calculating the torque you will need.

Then there are details about the current rating (or torque at such-and-such a current). And the voltage rating. You want to keep the voltage rating low, like in the 3 to 5 volt range so that the motor controller has some "headroom" drawing power from the 12V supply. The controller controls current, not voltage, and voltage will vary depending on what the motor is doing (the "rated voltage" is actually the static voltage when it's stationary, doing nothing; it needs a higher voltage to do something).

If you go outside the world of steppers provided with Printrbots (or typical 3D printers) and just Google for stepper motors, you'll find that there are other options, like motors with more than four leads. These would NOT be compatible with Printrboard electronics.

Wikipedia has an article about steppers, and there are other excellent resources linked in some old dusty posts in this forum (I think doing an advanced search with Mooselake as the author of the post will turn up something).
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Re: Confusion - Changing Stepper Motors

Postby thawkins » 2016-May-Mon-04-May

RetireeJay wrote:It turns out that there are quite a few specs to consider.
If you're re-using one of the existing motors, that simplifies things a bit. The wiring will be compatible with the Printrboard.
Standard steppers used in Printrbots are all 200 steps per revolution, and they are all NEMA-17 - which means that with the motor shaft facing you, the square is 1.7 inches across.

Next is the torque specification, and the deeper the motor the more torque it will be able to generate (that's pretty intuitive: bigger = stronger). So don't substitute a smaller motor for a bigger one unless you have a pretty good idea about calculating the torque you will need.

Then there are details about the current rating (or torque at such-and-such a current). And the voltage rating. You want to keep the voltage rating low, like in the 3 to 5 volt range so that the motor controller has some "headroom" drawing power from the 12V supply. The controller controls current, not voltage, and voltage will vary depending on what the motor is doing (the "rated voltage" is actually the static voltage when it's stationary, doing nothing; it needs a higher voltage to do something).

If you go outside the world of steppers provided with Printrbots (or typical 3D printers) and just Google for stepper motors, you'll find that there are other options, like motors with more than four leads. These would NOT be compatible with Printrboard electronics.

Wikipedia has an article about steppers, and there are other excellent resources linked in some old dusty posts in this forum (I think doing an advanced search with Mooselake as the author of the post will turn up something).


6 wire motors are usualy ok, the are usualy just the same as the 4 wire ones but with a center tap on each winding, you can just leave out the center tap connection, and they work the same as the 4 wire ones.
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Re: Confusion - Changing Stepper Motors

Postby RetireeJay » 2016-May-Mon-08-May

Thawkins is right; I should have said motors with more than 4 wires are not "plug-compatible."
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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Re: Confusion - Changing Stepper Motors

Postby Mooselake » 2016-May-Mon-09-May

Stepper motors, besides the obvious size differences, also have different motor windings. These lead to the different voltage and current ratings you'll see in the specifications. Power is voltage times current (we'll skip all the AC stuff...) which gives you an infinite range to get the same specs - one volt at one amp, a million volts at one microamp, for example. Plus, like a lot of things, there's a wide quality range. One motor might use old hardened sponges for bearings, one might use the finest ball bearings made of hardened higrade unobtanium. One lasts a couple minutes (short warranty...) and the other you'll hand down to your multi-great offspring - who will still be paying for them.

Read spec sheets (like the data sheet linked to this motor listing; actually if this one will work just use it...), comparing torque specs (think of them as relative, not usable numbers), voltage/current (no, you don't need 12V motors, the driver chip handles all that) keeping in mind that while you don't want to overheat the drivers with excessive current, you also don't want to slow down the motor speed with the increased inductance that lower current (and consequently higher voltage) rating motors will have. Chug through Kysan's tables of motor specs, see that the same size/torque motors are available in a wide range of voltage/current specs.

The real reason that almost everybody uses the same motors is because they're not design engineers with extensive knowledge of stepper motors (nor are moose in the great white north, they just read a lot). Most of the time the common motors just work, and cause they buy (or at least hope to buy) them by the semi full they get a good price.

To add to the winding fun, you can also use 8 wire motors, and get the option of series/parallel connections. Google if you care. Essentially if you buy new motors just get ones like you have, if you're into dumpster driving and disassemble old gadgets then the other factors become important. If it's your first time stay away from those trash piles. Design your new printer around the common motors, worry about the other things after you get a few printers (like the furball) on your resume. For your first design saving a couple bucks (or even tens of bucks) isn't as important as making something that's more likely to work the first time and not end up in a pile in the back of the closet - where you wasted all the expense.

If you use motors with similar voltage/current specs the same drivers will work, and you can accommodate any changes in steps/mm with configuration changes via gcode without changing the firmware.

Kirk
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