Hi Guys. I want to change my setup. I am going to take off the A4988 chips and put external drivers for bigger servos. Any one know if this work or have done this before.
I have a vague recollection that @Tatarize mentioned someone successfully doing that, but am having trouble coming up with the search terms to find a post… 
This work has been done, to my understanding at least twice.
There are two methods first you can replace the 4988s with a form factor permitted better stepper chip. Or two, you can expose the stepper board connections being sent to the 4988s and tap into those with some step-sticks. The latter is actually the preferred method. Because there’s a limited number of cross compatible stepper chips and you get a lot more control and access scraping into the board wires.
This is the first I knew of it, I suggested this to somebody who had blown up his stepper and apparently he was like, “that’s a great idea” and did it with the latter method. Now the original author of that post has since used that better method of exposing the wires going to the 4988s to hack into the signals.
We’ve done logical analysis and the signals being sent from the CPU to the 4988s are pretty basic. Ticks and switch forward/backwards. That’s apparently perfectly easy to hack into and you don’t really even need to disconnect or mess with the 4988s apparently if you were gingerly enough you could even just take in the signal to the step sticks and tap into the signals and just not plug anything into the 4988s and it wouldn’t really matter much.
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Just to come back to every one. I have done exactly as in my picture and its working fine. Thank you for the info.
This was the cheapest fastest way to convert my 1300 x 900 laser cuter . As I say before I love K40wisperer and Meerk40t so i have change my laser to work with it.
Thank you all
May you have great progress with everything you do and have a great day.
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could you share a picture of the final job pls?
Hello @Adolph_Smith_snr, I know this is an old thread but I’m looking to do your exact same mod. Can you share some details?
For instance:
- did you trace only those four wires from M2 to driver or there are more?
- what about the other highlited pins? From my understanding I shall be able to set them on external driver directly, for instance the microstepping set with dipswitches instead of 3 wires on allegro chips.
- how did you provide supply to drivers? Did you put an additional power source directly to the external drivers, eventually, what’s the voltage?
Could you share some pics of the setup?
Thanks