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HobbyCNC Pro Driver Board

Posted: Wed Feb 19, 2014 2:27 pm
by samc99us
Ladies and Gentleman,

I'm not sure where the best place to post this is. I will likely duplicate it in my build log, and across the internet. I have a HobbyCNC Pro Driver board I assembled 2 years ago, and have never been happy with. Lost steps on an ACME drive system with dumpsterCNC antibacklash nuts and associated NEMA23 couplers using the HobbyCNC NEMA23's. The driver software was GMFC through a GGC USB->parallel converter board, which also includes a board level clock, and was driven from a laptop.

I have been using the same board on my SO2 with a completely different set of motors, wiring, new enclosure, different PC (direct parallel port connection) and LinuxCNC. Over the weekend I was doing some test cuts to narrow down the accuracy of my system, when I noticed I was 1/32" off over a 2" travel distance in my X-axis, but spot on in my Y-axis. I make the required change in LinuxCNC, x-axis is spot on but now the y-axis is off!! WTF? Two different setups entirely (mechanical and electrical, save the HobbyCNC board), and the same damn issue!! So I did some digging, and came across these two threads:

http://www.cnczone.com/forums/joes_cnc_ ... mach3.html
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?HobbyCNC

Hey, wait a second, lost steps even with current reduction disabled? That sounds like me! So I followed the white wire mod on CNCZone last night and WOW. It is night and day different. Waaay smoother on startup. No lost steps or semblance of lost steps. I dialed in my X and Y-axis travels and am well under 1/64" error.

Exact steps:

1) Read post 1 from the CNCZone thread
2) Print this picture out and make your board look identical: http://www.cnczone.com/forums/attachmen ... ermods.jpg
3) Add a 10K ohm resistor across the outside legs of one of the removed transistors (per #16)
4) Set "Amplifier Enable" to Pin1 in the StepConfig of LinuxCNC. This enables idle current reduction when the machine is in stop mode (orange power button depressed in LinuxCNC) and disables idle current reduction when the machine is commanded hot from LinuxCNC. Works like a charm.

If you are handy with soldering, I can now recommend this electronics setup for LinuxCNC. If you're not, I'd point you towards a Gecko540.

Best,
Sam

Re: HobbyCNC Pro Driver Board

Posted: Wed Feb 19, 2014 2:39 pm
by cvoinescu
That's excellent advice and a great mod. The circuit as designed is pretty stupid, to be honest. The same design error affects cheap TB5650 drivers.

I have one thing to add to your recommendation: the HobbyCNC board is for unipolar stepper motors. Many people have bipolar stepper motors, and the board would not work for them.

Re: HobbyCNC Pro Driver Board

Posted: Wed Feb 19, 2014 2:54 pm
by samc99us
That is a big thing to note. It's also a complete pain, forcing the use of more expensive 6 or 8 conductor wire, which I have yet to find in a shielded variety for less than $300 for a 300' roll.

If building from scratch, I would get the Gecko 540 and move on. If you can score a deal on a built HobbyCNC driver board that is in known working condition, this is an excellent option.