Bigger motors on A4988 drivers?
October 01, 2017 01:57PM
Hi,

my new CoreXY build has two NEMA 23 motors running X and Y and even a NEMA 34 motor (since I had it laying around) on the Z axle. I have used external drivers and breakout boards on my RAMPS 1.4. Everything is on 24V with a better regulator soldered onto the Arduino Mega. So far, so good. I set the extruder driver, an A4988 on the RAMPS, to 1A. This works great, no clicking, good feed, me happy. But this made me think. All four driver, the three big ones off board and the small A4988 are on 24V and limited to 1A, and working great. Why couldn't I run the bigger motors on A4988 drivers, if all they require are the 24V and 1A current limit? My feeling is the bigger motors need the big drivers, but the numbers I think say I could run them from the A4988s on the RAMPS. Cleaning up the set-up considerably. The A4988 I have are supposedly good up to 2A.

Am I correct, is 24V, 1A limit (and the same microstep settings) all I need to consider, so I can run all from A4988 drivers on the RAMPS?

Cheers,

Hugo

Edited 1 time(s). Last edit at 10/01/2017 02:06PM by HugoW.
Re: Bigger motors on A4988 drivers?
October 01, 2017 05:24PM
As long as you under the Amp and voltage limit. The A4988 is fine.

Most opt for external driver on nema34 as they choose stepper that need over 1.5 amp.
Re: Bigger motors on A4988 drivers?
October 05, 2017 05:48AM
My take on it is that whilst the actual torque generated by a given motor is not always exactly proportional to its current, this is still a good guide to how "powerful" the motor is. So if you don't need powerful motors that require more than 2A (you'd need to cool the drivers pretty well - from underneath - at this power level) then you can either - just use nema 17's running at 1A, they're smaller and quieter and if you feed them 1A you'll get roughly the same power as you will feeding a nema 34 1A. Or as you have larger motors already, then run them at 1A directly and if this enough then your all good. But its considerably underpowering your larger motors - sell them and buy some nema 17's and pocket the difference.


Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
Re: Bigger motors on A4988 drivers?
October 06, 2017 01:33AM
I was given the two NEMA 23 motors currently running the X and Y on my CoreXY machine, the 34 I still had in the parts bin. I might swap out the 34 at a later stage, but building the printer is not my first priority, printing RC car parts is. And that is working. I just feel the machine is very noisy, especially the big fans I have inside the power source (way overkill item again, also given to me), and a radial fan blowing over the large external drivers. I now found the DRV8825 drivers. They should be able to handle 2A, so 1A won't be a problem, and fit the RAMPS directly. I just printed out a RAMPS enclosure which will hold one quiet 50mm fan and I bought a 24V 10A power source from Aliexpress which shouldn't need any cooling other than not being enclosed.

I even consider to reduce the traveling speed of the machine (printing is done at 60mm, no problem there) a bit and use 32 step microstepping to quiet it down even further. I found this page: [reprap.org]. It says the table should be reworked but it's all I have at the momtent. I use 20T pullies on 1.8 degree steppers, RAMPS controls running Marlin. So on 32 microstep mode, I should be able to run traveling speed of 100mm/s.

Hugo
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