Ramps 1.4 External Driver Hookup

I’m currently trying to use an OX router as a 3D printer to print some parts so that I can build a proper printer. X, Z, E axis all working perfectly!

Y axis continues to lose steps. I’m driving 2 Nema 23’s on the Y axis and assume the A4988 onboard driver can’t handle the load?!?!? I’ve slowed down feed rate, jerk, and acceleration to the point that it’s excruciating to watch it print.

Can I just wire STEP-DIR-EN-5V from the Ramps shield to an external driver? Do I have to worry about voltages ie 3.3v or 5v compatibility?


Hello, Scott.

It is possible that the A4988 is underpowered for the stepper motors you are using; if the A4988’s current limit is configured to a setting that is limiting their current to something much less than your stepper motors are rated for, you will not be getting the full torque they are capable of. The NEMA size that you gave only refers to the size of the faceplate on the stepper motor and does not give information about its specifications, so I cannot say if our A4988 carrier is appropriate for your motors. I am not very familiar with the RAMPS 1.4 (we do not manufacture or sell it), but our DRV8825 carrier might be a better choice if you need more current, and it can be used as a drop in replacement for our A4988 carrier in many applications. You can find a list of differences on the DRV8825 carrier’s product page. You might try checking your stepper motor specifications and comparing them to the DRV8825 carrier to see if it is appropriate.


Can I just wire STEP-DIR-EN-5V from the Ramps shield to an external driver? Do I have to worry about voltages ie 3.3v or 5v compatibility?[/quote]

Typically, 2 NEMA23s would be much more than a single A4988 could drive, quite possibly more than a DRV8825 could handle. They tend to draw 1-3+ amps per phase each, depending on the winding and depth. That said, even if you had a low amperage NEMA23, you might have a problem running fast, with the inductance of that nema, since it would probably be a higher voltage rated NEMA23 to facilitate low amperage.

You have a couple options.

(1) wiring the NEMA23s to two different drivers. You probably need to set it to “FULL step” if you do this, since microstepping might be a tiny bit off between the drivers (I dont know fully, but I understand you can’t assume the two to work exactly the same when driven by two drivers in microstepping.) The good news is you can wire the EN/STEP/DIR to both drivers in parallel, so the code doesnt need to change.

(2) Running an external driver will work too, as you mentioned it, but you want to make sure your external driver can handle 5V singles, since the RAMPS is a 5V device.

(2)a), I don’t know if you have access to decent stepper drivers, but the ones better than DRV8825 tend to cost a bit of $$. There is a common Toshiba 3.5A-4A driver that is cheap on ebay, but do your review searches because I understand they are often poorly made and can blow up pretty easily.

(3) if your code, and I believe RAMPS is ok, does not have a 2uS pause on the signal, it may have a problem with some drivers like the DRV8825 which requires a >2uS pause (the a4988 is 1us). This usually isn’t a problem though, so I dont think you need to worry.

Brandon is right that NEMA23 isn’t enough information, but “chances are” the a4988 is not sufficient. You suggest wiring an external driver…and, yeah, if it follows the step/dir protocol, and can tolerate 5V, you should be in business.