Is it possible to use external drivers with the Rambo v1.4 board? I really like my MPCNC, but I’m building a different CNC machine. I like the dual end stops and I like that in the future I could use more than 3 axis, so I’d like to re-use the Rambo v1.4 and firmware but upgrade to larger motors, but I wasn’t sure if it’s possible to use external drivers with this board. The motors I want to use are NEMA 23 175 oz*in with 2.8A/phase (12-48VDC). I don’t think I can use them with the since the onboard A4982 drivers seem limited to a lesser amperage. I can’t really find good information on this so I’m not positive.
To be clear, I understand that NEMA 23 is only a mount size, but I do want higher torque motors than the original MPCNC motors because my new machine is beefier (it’s a gantry design with ballscrews and linear rails).
Does anyone have any experience with this?
AFAIK, the rambo connections between the processor and the drivers are just traces on the board. You don’t need to carry any current on those wires, so with some small wire (28ga or smaller) you might be able to find the pins and solder directly to the pads. But honestly, it isn’t really worth it, and there’s a decent change you’ll short something, especially if you aren’t experienced with that kind of small soldering.
You could get closer to 2A with some good cooling on the chips, which might be more than the motors can actually handle without getting too hot. That might be worth a try.
You could also get a board like the SKR v1.3. That would support dual endstops, and you’d just configure it for drv8825 drivers, and connect GND, STEP, EN, DIR to your external drivers. The RAMPS would work too, but I am just not sure where to get one that is decent quality.
Jeff, I appreciate your input. I ended up just buying a RAMPS board and we’ll see how that goes once I get it and it’s installed. Thank you!
Id like to jump in here and ask if I can do this with the SKR Pro V1.2 that I got from here. I do not see where the GND, STEP, EN, DIR pins are. Can you help on this?
You will have to pull the TMC2209 stepper drivers in order to install external drivers. Pay attention to the orientation of the stepper driver when you pull them, and look at a pinout for the 2209 like this one. In addition, usually the pins are labeled on the driver board. Also I did a quick bit of searching before answering your question and found this adaptor that plugs into where the stepper drivers would be and provides a four pin plug for an external driver. It is made for MKS boards but it should work for the SKR Pro 1.2. Personally if I was doing this, I’d be tempted to solder up something similar that just consolidates the four pins for each external driver in order to simplify and idiotproof my wiring.
Thanks for your quick and informative response. I just happen to have a few of these MKS adapters that I purchased a while back. I have been leery of using them as I have no idea what the circuitry on them is all about, I sent a question in to Steppers on line to see if they will send a schematic out for the DM542Y drivers that I have and plan to use on my machine. There is a 4 position female plug inside the unit that may be where the MKS adapter plugs in. As yet I am not sure. Making my own sounds intriguing if I knew what pins to tap into.
Making my own sounds intriguing if I knew what pins to tap into.
Looking down at the stepper driver, you want to make something like the following. The pins to tap into are highlighted in yellow.
This plugs right into were you pull the TMC2209 drivers. The only question is orientation. You can get that by looking at this image and comparing it to the installed drivers before you pull them.
According to the description at the link I provided, the circuitry optically decouples the input and output of pins reducing the current draw on the pins of the control board. I’m only a hobbyist with electronics, but the description makes sense and is potentially beneficial…and in some situations may even be necessary.