What kind of Nema 17's work best with RAMPS

Hello,

anyone here know if I am building a 3D printer if I should use 0.4A or 2.0A Nema 17's with a RAMPS board? 0.4A motors seem to be the standard for i3 clones but I found some 2.0A motors for cheap and was wondering if these could only be used for CNC specific RAMPS/Arduino systems and prevented them from being used for 3D printer applications.

Neither is well suited to 12V operation and the under-cooled plug-in drivers used on RAMPS. Look for motors with rated current between about 1.0 and 1.5A.

Edited 1 time(s). Last edit at 12/17/2017 02:48PM 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].

What do you mean by it not being suited for 12V operation? Sorry, still new to circuits.

Let's say I used a 12V30A power supply and some DRV8825's, would that solve the 12V operation problem and the cooling for the drivers?

0.4A Nema 17 motors need more than 12V to make them move at reasonable speeds. DRV8825 drivers have issues with low current microstepping so are best avoided.

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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, that makes sense about the 0.4A motors.

First I ever heard of the DRV8825's having a problem with their microstepping, got any sources? Also, if you had to choose between A4988's and DRV8825's for 2.0A and 1.5A motors which would you choose? I know there are some really nice TMC2130 drivers out on the market but just two of them cost the same as my RAMPS and Arduino. I think it's probably best that I just wait a couple months for their hype to go down before I upgrade to them.

[reprap.org]

Found what you were talking about the DRV8825's losing steps but that is only for 24V power supplies when using low amp motors

I'm sure I have some 2amp ones seem to be ok but I cool the drivers, I thought the adverts for them all where misleading, ie they put the amps & the oz through some calcs to appeal to different people? but then my electronics knowledge is less than Zero,
My logic was if i got a powerful stepper but wasnt running it at full power I wouldnt get the specified performance, but as long as it moved I would get out of it enough for my needs, and I could get more out of it in the future. The crazy thing is I have no idea where the 2amp ones are or what the others are, I assume the smaller ones are the lower amps.

Generally speaking, longer bodied NEMA17s have a higher current rating, so yes, the thinner pancake motors are usually lower amps. I've heard of a few issues regarding the DRV drivers, most notably the microstepping issue mentioned about and some whine issues. I think the A4988 are better suited for most applications, but like dc42 says plug in drivers under perform compared to integrated drivers (where the chip is mounted directly on the control board). Saving a couple of bucks with a ramps/mega/drivers compared to a cheap all in one isn't really worth it. When you total the cost the difference is really just a couple of bucks and you get better performance, less wiring, mess and hassle and (my favorite) don't have to fiddle with trim pots.

From what I know about 12 vs 24 volt, 24 volt lets you push more current through the coils of the motor faster, and where this comes in most notably is like dc42 said with trying to drive motors fast and with a high switching frequency for the coils. Each motor needs a certain voltage (which creates a current) across its windings to turn, and running them at 24 volts allows to overcome the inductance of the coils and reach that points faster than when running at 12 volts. The inductance of course has a more prominent effect at higher frequencies. You also get more torque but I personally think you get enough torque at 12V. The bigger perks of 24V are to do with the heaters, in my opinion.

The three main attributes to consider of a stepper are torque, current, and inductance. Specifying one without the others is rather meaningless. You can have a 20 oz-in motor that draws 2 amps or a 90 oz-in motor that draws 1.5 amps.

Here's a good explanation of stepper speed and torque: [www.nmbtc.com]
This spreadsheet may also help: [github.com]

Hey MechaBits, this is the link for where I found the 2A stepper motors, looks dodgy but I can hound Walmart down for anything that might go wrong.

[www.walmart.com]

Thanks for the great tip on cooling the steppers, gonna pick up an extra fan just for that!

Thanks for the advice Trakyan, I get what you're saying, I wanted to start with something cheap that I could try hooking up a cheap $2 wifi module I found, since there's more support for RAMPS it helps me with the wiring and downloading the open source SCARA firmware. Inbetween all these shenanigans, it means if I break the board, it's pretty easy to repair. I am certainly going to upgrade the board in the future, probably by plugging in a 32-bit Re-Arm board and some TMC2130's when their prices go down with their hype. If you still think a single board would be better, I'm budgeting any upgrade for under $75. Sadly, that shoots down the gloriously overrated duet wifi board but feel free to shoot me any suggestions!

Also, thanks a ton with explaining voltages, I did not know much of that!

Edited 1 time(s). Last edit at 12/19/2017 11:03AM by Power3DPrinting.

I'm not cooling the steppers just the drivers, but I just bought some new steppers 100oz 1.5 amps, wanted all black but also wanted the removable lead more.
[www.ebay.co.uk]

Things like the rumba and the mks base are basically a ramps, mega and stepper drivers all on one board (rumba still uses replaceable drivers, though). Same firmware, same pinouts, but some better connectors and less things to go wrong (imo). The price isn't too much higher, definately well under your $75 dollar budget, you could probably buy 2/3 boards for the price or one board and one of those 32 bit controller modules to go with it like the tft32, or a raspberry pi or something.

Now that you mention you want to make a SCARA though, you might benefit from 32 bit electronics off the bat. SCARA has trigonometric functions in its inverse kinematics, these are pretty computationally intensive and 8 bit processors can really struggle. There are cheap 32 bit controllers from china like the mks sbase, or you can try something like klipper (firmware) to make SCARA kinematics work on 8 bit, but I don't know if klipper supports SCARA yet. You could also buy a chinese knockoff smoothieboard. 32 bit boards even from china will cost you upwards of $40 though compared to the 15-20 for the cheaper 8 bit boards, but still under your $75 budget.

Thanks a ton for the suggestions Trakyan! I've never heard of some of these boards before so I'll check them out. I think you're right having something 32 bit off the bat would be desirable, I'll try and get in touch with some SCARA builders I know and see if they've been shut down by 8-bit controllers.

FWIW I posted a series of three blog entries on improving a cheap SCARA printer kit, including the effects of replacing the original 8-bit electronics by a Duet Ethernet. You can find the first one at [miscsolutions.wordpress.com]. The following one covers the electronics conversion.

Edited 2 time(s). Last edit at 12/20/2017 12:29PM 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].