10 lb Y Carriage - Geared Stepper Motor or Triple Stack Nema 17?

I have a dilemma. My Y Carriage is huge; I have a 8.5 pound (4~ kg) piece of aluminum tooling plate with a silicone heater, an under layer, and various linear motion components and fasteners. All in all I would guess it weights between 9 - 10 lbs. Moving the entire Y carriage on 4 cheap Chinese lm8uu bearings is a small single stack Nema 17 stepper with 36 oz-in of torque ( Ebay Page ). I have cranked this poor stepper motor beyond the point where it will burn anyone who dare touch it, but yet it is still unable to drive my bed back and forth with greater than 500mm/s of acceleration without introducing resonances.

This leads me to the big question. Should I use a geared stepper, a triple stack Nema 17 or even a Nema 23 to move my 10 pound Y carriage with decent acceleration? (Also cudos if it fits within the same footprint as the existing Nema 17)

Geared Stepper Example: Ebay
Triple Stack Stepper Example: Ebay
Nema 23 Example: Ebay
Geared Nema 23Example: Ebay

My electronics include:
Ramps 1.4 Clone
A4988 Stepper Drivers
PC Power Supply

Thanks for any help!

Edit:
For those viewing this thread later there are a handful of key takeaways when choosing steppers
1. Geared steppers are not typically used as they introduce backlash, if you need high torque look at nema 23 motors before you consider geared motors.
2. Use this Link to calculate the motor strength you will need (Use a 2x saftey factor).
3. Double the holding torque that the motor size calculator gives you.
4. Shop for a motor that has a holding torque that exceeds the final oz-in you calculate
5. Buy electronics (Stepper Drivers) that can handle the stepper's current draw.

Edited 3 time(s). Last edit at 07/07/2016 05:11PM by Trexation.

The stepper you are using is a poor choice for driving the y axis.It is a 12 volt motor so it has a high resistance and would be slow even with a light load.
You need a motor with 2-to 3 volts at 1.6 amps or so.
The geared motors at 14:1 means it has to run 14 times faster to get the same speed out. You sacrifice speed for power. Also they have backlash as stated int the ebay description which is very bad for printing.
Nema23 motors would be better except you would need to rebuild your mounting and you would also need to buy external drivers as the A4988 will not dive them.

A good nema17 would be much better than your current motor.
Good means low inductance and high amps.
for example:
* Holding Torque: 59Ncm(83.6oz.in)
* Rated Current/phase: 1.7A
* Phase Resistance: 1.4ohms 1.4 ohm X 1.7A = 2.38 Volts
* Inductance: 3.0mH+/-20%(1KHz)

Also with 4 bearings you have to be very sure your rods are parallel or you will have binding

George

Wow! Where to begin??...

Very massive beds and 8 mm end supported rails do not work. 8 mm end supported rails are barely adequate for "normal" printers. With that huge bed plate you've got, they will surely sag. Your bed will be moving in a curve, not a plane. For a massive bed like that you need fully supported rails of some sort. I am partial to linear guides.

You can drive any size motor that uses up to about 1.5A using a RAMPS board with stepper driver modules. NEMA-17 and 23 refer to mechanical size, specifically the diameter and bolt spacing, and say nothing about performance. Motors are sized based on what they are expected to do. The Oriental Motor web site has motor sizing tools that you can use to calculate the required torque to deliver the performance you want. Once you know the required torque, you shop for the motor, then you shop for the electronics to drive it. NEMA-17 motors top out at about 100 oz-in. If you need more than that, start looking at NEMA-23 motors. In general, NEMA-23 motors vibrate more than NEMA-17 motors, so be prepared for some extra noise.

Three bearings should be enough to fully constrain the motion of the bed, and 3 leveling screws will actually level it, while a 4th will cause the undercarriage to bend.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Even with a stronger stepper, wouldn't the small GT2 belt cause problems then?

Thanks for all of the support!

I have calculated the torque that my stepper will need, here are my calculations and testing methodology.

The Test - See the picture ( picture is before I removed motor resistance )
In short I used a clothes hangers as weights to determine the amount of force required

The Math
6 Hangers * 8oz each¹ = 48oz
.479in diameter pulley * 48oz = 22.992oz-in

1. Based on this amazon listing; I do not currently own a small scale.

My conclusion from this is to buy a better Nema 17 motor and get linear rails unless other people have different ideas.

These are what you have in mind correct? qMAAOSwu4BVn9gW" target="_blank" rel="nofollow">Ebay and this Ebay

Edited 1 time(s). Last edit at 07/06/2016 11:05AM by Trexation.

Quote
Trexation
Thanks for all of the support!

I have calculated the torque that my stepper will need, here are my calculations and testing methodology.

The Test - See the picture ( picture is before I removed motor resistance )
In short I used a clothes hangers as weights to determine the amount of force required

That isn't even close to the way you calculate the required torque. Required torque is a function of acceleration, maximum speed, inertia of moving parts, desired stopping precision, friction, etc. Go to Oriental Motor's site and try out their calculators. If you can use turbotax to do your taxes, you can calculate the required torque. After you have a torque value, check the torque vs speed curve for the motor you select and make sure the motor can deliver the required torque at speed. Unfortunately, most of the cheapo motors that come from China lack torque vs speed data. In that case either buy a better, more tested motor, or find one that has similar specs to a cheapo motor and assume they perform the same. Keep in mind the old adage "when you assume you make and ass of u and me"

Edited 1 time(s). Last edit at 07/07/2016 01:01AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

So I tried out the oriental motor site, and here is what I got.. (See pictures below) it was about 32 oz-in of torque with a 2x safety factor.

Edited 1 time(s). Last edit at 07/07/2016 10:20AM by Trexation.

I'm no expert on it, but your numbers look about right to me. I'm surprised such a small motor can do that, but we'll know for sure when you try it. Now find a motor that has that torque when it's turning at 450 rpm (7.5 revs per sec to move the extruder at 300 mm/sec).

Torque vs speed curves look like this:



See: [www.nmbtc.com] and click on the motor selection tips icon on your 3rd image.

Edited 1 time(s). Last edit at 07/07/2016 11:46AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
I'm no expert on it, but your numbers look about right to me. I'm surprised such a small motor can do that, but we'll know for sure when you try it. Now find a motor that has that torque when it's turning at 450 rpm (7.5 revs per sec to move the extruder at 300 mm/sec).

Torque vs speed curves look like this:

See: [www.nmbtc.com] and click on the motor selection tips icon on your 3rd image.

That page is misleading, because it appears to assume constant voltage drive, not constant current drive. When using constant-current drive (as we always do in 3D printers):

- The "electrical time constant" mentioned at the bottom of the page is irrelevant;

- The speed at which the torque starts to fall off depends on the the voltage of the supply to the drivers - which is probably why manufacturers don't publish torque vs. speed curves any more;

- The drop-of curve doesn't look like that diagram. It is essentially flat up to the point at which the driver supply voltage is insufficient to overcome the combination of the back emf of the motor due to movement, and the back emf due to inductance as the driver tries to reverse the current fast enough to achieve the required speed.

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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].

I think that I have finally found some decent stepper motors at this qMAAOSwu4BVn9gW" target="_blank" rel="nofollow">link, at $11.60 per stepper they are also not a bad price. Thanks for all the help digital dentist!

Edited 1 time(s). Last edit at 07/07/2016 03:59PM by Trexation.

Quote
Trexation
I think that I have finally found some decent stepper motors at this qMAAOSwu4BVn9gW" target="_blank" rel="nofollow">link, at $11.60 per stepper they are also not a bad price. Thanks for all the help digital dentist!

Those are good motors, however you really need better electronics to drive them. Your RAMPS/A4988 electronics will only manage a little over half their rated current (hence half the quoted torque), even with a fan to cool the drivers.

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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].

Would DRV8825 Drivers be a better choice? They are rated for 2.5A compared to the 2A provided by my A4988.
The Ebay Link

Edited 1 time(s). Last edit at 07/07/2016 05:06PM by Trexation.

Depends where you get the stepper drivers from.... cheap Chinese versions will probably struggle to do much. A conservative estimate is that they'l do 70% of advertised rate... Buy direct from pololu and they'll do better. Even then, this is all on paper... It's very dependant on how well you cool them. The little heat sinks you get do very little. Larger heat sinks may be needed. Or just buy a few DRV's and see what happens... China is cheap, great for experimenting.

I use DRV8825's on RAMPS 1.4 (12v power supply), and I struggle to get more than than 1.6 / 1.7A out of them. That's with a large 120mm fan on them and the mini heat sinks they supply. Perhaps better ducting of airflow, or bigger heat sinks, thermal paste etc may work. I run 2A nema 17's, and my bed currently weighs 1.2kg's.

Okay, I will keep that in mind and thanks for the help!

DRV8825 drivers can be problematic in some builds, depending on the motor inductance and the power supply voltage you use. The symptom is that they skip microsteps, leading to a loss of resolution. This affects delta printers worse than Cartesian printers. See [cabristor.blogspot.co.uk] for more.

The plug-in ones can handle a little more current than the A4988s, but not much more. To get anywhere near 2A, you need electronics with on-board drivers, because they cool the driver chips much better than plug-in drivers can.

Edited 2 time(s). Last edit at 07/08/2016 04:29AM by dc42.

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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].

Will running my motors at 3/4 of their rated current really be that bad?

If I am able to achieve 65% of the 2.5A max rated current that DRV8825 would provide would be 1.625A
My motors can handle 2A
Thus 1.625A/2A = 81.3% of total possible current
.813 * 84 oz-in = 68 oz-in max torque
(4x the torque required)

LOL, I could attach one of Link... I think

Edited 3 time(s). Last edit at 07/08/2016 09:46AM by Trexation.

The 2.5A rated current of the DRV8825 assumes that the thermal pad on the bottom of the chip is soldered to a large area of printed circuit board to remove the heat. The plug-in drivers provide nothing like enough area. This one [www.panucatt.com] may be a little better when used with a heatsink and fan than most, because the heatsink removes heat from the underside of the chip (where the thermal pad is) instead of the top (which is plastic with poor thermal conductivity).

But to repeat and expand on my earlier advice: DO NOT use plug-in stepper driver modules other than on small printers with appropriately-rated motors.

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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].

A 10 dollars a driver those are really expensive... At that point I would probably just buy this if I could connect it to my ramps... Would that be possible?

Quote
Trexation
A 10 dollars a driver those are really expensive... At that point I would probably just buy this if I could connect it to my ramps... Would that be possible?

Yes, you should be able to connect those to RAMPS. But a large and obviously expensive printer really deserves better electronics than Arduino/RAMPS anyway.

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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].

Thanks for all the help! For stepper drivers I will probably just get DRV8825s and cool them as well as I possibly can.