Using ramps with bigger stepper drivers?

Hi guys - please excuse my newbie questions,.. I've been doing loads of research & I'm still confused, so I reckon asking the experts to point me in the right direction might be a good idea!

I'm relatively new to 3D printing - but I've a working Prusa i3 that is producing some very nice prints & I'm really happy with,.. and now I want to build bigger, so I'm trying my hand at building a DIY CNC machine to compliment my printer.

I thought CNC machines would be simple - no hotend, no heated bed, slower motion & simpler toolpaths,... but when I started looking it was like stepping bac in time 15 years! Everyone seems to use Mach3 and a dedicated PC to run the machine, which seems overkill when more complex 3d printers will happily run from an SD card on a ramps controller using designss created in free software!

So - I want a ramps style controller to run my CNC mill - SD card support, LCD screen & controls - simple, compact & affordable.

But here's my issue: The standard ramps stepper drivers max out at 2.5A even with additional cooling - and the Nema 23 motors I reckon I'm going to need require 3A - So I'm looking for larger stepper drivers that are compatible with ramps & wiring diagrams to make them work,.. can anyone point me in the right direction?

Alternatively - what are the most powerful stepper motors I can drive from a standard ramps board?

I'm using two of these: [www.sainsmart.com] in my printer, with 32V power supplies. These drivers can handle up to 50V supplies.

The inputs are optoisolated, so you can safely connect to the RAMPS board without fear of destroying it. You need to pull the step, direction, and enable signals and a ground connection from the stepper module sockets.

And they work fine with standard firmware? I've read alot of people talking about the ramps pulse width being too short for many of the larger stepper drivers?

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the_digital_dentist
I'm using two of these: [www.sainsmart.com] in my printer, with 32V power supplies. These drivers can handle up to 50V supplies.

The inputs are optoisolated, so you can safely connect to the RAMPS board without fear of destroying it. You need to pull the step, direction, and enable signals and a ground connection from the stepper module sockets.

Not sure about RAMPS, but the 1us pulses out of my smoothieboard work fine. It's unlikely that RAMPS uses shorter pulses than that since the A4988 chip data sheet says 1 us typical pulse...

Thats awesome to know, thanks!

I'm also researching what are the biggest motors I can use on a standard stepstick/ramps setup & possibly slaving 2 channels together for the Y axis,... it'd save a nice bit of cash (Budget is tight for this project!) and get me started quickly, with the aim to upgrade once the machine has completed a few paid jobs,..

NEMA-17 motors max out at about 100 oz-in torque. NEMA-23s start maybe a little lower than that and go up to about 500 oz--in. NEMA-23s in the 100-150 oz-in range run about 2A (at least the ones I have do), and can be driven by pololu modules (I was doing it for about 2 years with no problems). I have a 425 oz-in motor in my Y axis that uses 2.8A.

Before you beef up the motors you might calculate the torque required. Check the motor sizing tool at Oriental Motor web site. [www.orientalmotor.com] Once you know the torque, shop for the motor, then find a suitable driver and power supply.

My calculations are rough - but I'm thinking 270 - 300oz would do the trick for me.

My X and Z axis will definitely have enough power at this,.. my only real concern is driving the Y axis to move the gantry. I'm building in 18mm HDPE so there will be about 35kg with all the hardware included & my budget has restricted me to some fairly basic DIY rails which will undoubtedly have a lot more friction than I'd like. My plan at the moment is to buy 4 steppers with the aim of building a 4 axis machine, but if the Y axis has issues I'll put the 4th axis on hold & I'll be looking for a way to slave the extruder output on ramps to duplicate the Y axis output & use 2 steppers to power it...

Would it be silly to try these motors with the DR8825 stepper drivers - with extra cooling of course?
[www.ebay.ie]

Ok - final silly newbie question for tonight - my apologies in advance:

So the link in my last post is 3A Nema 23's that produce 270oz - but I've just seen bipolar Nema 23's (link below) that produce 290oz and are rated at 1A??? How is it possible that there could be more power output with 1/3d of the current? Will the DRV8825 drivers cope with these ok? Are bipolar motors really that much better or is there a drawback I don't know about?

[www.ebay.com]

They have higher resistance coils, so take a greater voltage to drive the 1A. Work is VI, so the laws of physics remain unbroken. I'd expect the DRV8825 to drive them fine, but you'd probably need 24 to 36V to get good step rates and that would present a challenge if you host the drivers on a RAMPS board. a good quality RAMPS will have 35V capacitors, so it should be possible to run it to 24V. Watch out for budget boards that have 16V capacitors. There are some issues to running RAMPS at >12V, but there's info here [rigidtalk.com]

Edited 1 time(s). Last edit at 05/09/2015 06:08PM by JamesK.

Generally a similarly sized stepper motor that has higher torque will also have a lower top speed. You can see it on the datasheet as higher inductance.

Hi!
There are planetary gear for steppers out there. If speed isn´t a concern, you could use 12V and low amps and still have plenty of torque!

-Olaf

Thanks for all your advise guys - and can I just say that you've all been so much more helpful here than the CNC forum I asked the same questions on, where their only real advice was "buy this instead, its ten times your budget but worth it"!

I think the slower machine running from standard DRV8825 drivers is the right place for me to start on my very limited budget - but once I've a few paid jobs completed any profit will be put back into upgrades!

Now I just have to figure out the software - I'll open a new thread forhelp with that one though!

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JamesK
They have higher resistance coils, so take a greater voltage to drive the 1A. Work is VI, so the laws of physics remain unbroken. I'd expect the DRV8825 to drive them fine, but you'd probably need 24 to 36V to get good step rates and that would present a challenge if you host the drivers on a RAMPS board. a good quality RAMPS will have 35V capacitors, so it should be possible to run it to 24V. Watch out for budget boards that have 16V capacitors. There are some issues to running RAMPS at >12V, but there's info here [rigidtalk.com]

If you meant these steppers, you´d use an adapterboard between driver and RAMPS. Don´t connect 12V, but a seperate PSU. GND is common ofcourse.

-Olaf

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Olaf
you´d use an adapterboard between driver and RAMPS

That's a nice idea. You could probably connect straight into the existing driver sockets to pick up the ground and control lines and then put suitable voltage rated decoupling capacitors on the adapter board, leaving the rest of the RAMPS circuitry unchanged. With the adapter only having to deal with the stepper drivers it should be easy to fit 100v 100uF electrolytics on there, which would let you use the full 45V rating of the 8825s. Those things are amazing value for money!

I realize that these may be outside of the hobbyist's wallet but here is something that can be attached to the RAMPS signals output and run the printers. Now... no slobbering over a max microstepping of 51200 steps / rev ;-)

[www2.baldor.com]

Hi Dentist...you're using two of the Stainsmart drivers for your printer. Can you run multiple steppers on each of these drivers. My cartesian printer build is using two N23s on both the Z and Y axis with a single N17 on the X. I haven't come to a decision on which microcontroller to use but I'm interested in using drivers with these capabilities. Thanks.

1 driver = 1 motor, unless you want to connect the motors in parallel or series. The driver can handle 4.5 A, I think.

Are the motors in the Z axis lifting the X axis or the bed? I'd avoid 2 motors- add pulleys and a belt to a single motor. Axis orthogonality and bed level mid-print should not be subject to a screw binding and causing a motor to skip steps, or a wiring problem. It doesn't normally take a lot of torque to lift the X axis- I have a 110 oz-in motor driving both Z axis screws in my machine and it has a pretty heavy weight X axis.

Why two motors in the Y axis?

The bed is fixed to the table so the motors are lifting the Z/X frame work much like the 3DP Unlimited printer. [3dpunlimited.com] . I am contemplating running an axle rod between the two idler pulleys for Y axis; possibly even for the Z. I bought a 24v power supply for everything but I may add more for the separate axis if I go with the type of drivers you posted. I need to learn more about that setup. I'm using synchromesh cables for all 3 drives. I'm using dual motors on the Y and Z because of the mass of the carriage. The heat bed is 560mm X 760, the Z height spans 890mm. Its all stainless with v-slot aluminum extrusions. I'm still trying to decide on the best microcontroller for my application.