bdurbrow
commented
5 years ago In theory, if the wires are all run in grounded metal conduit, interference shouldn't be a major problem (reflections & termination might be an issue, however).
Of course, in theory, there is no difference between theory and practice, but in practice... well, you get the idea.
For my larger machines, I'm using GeckoDrive G203V drivers for the axis motors. The GeckoDrives will be mounted in a separate electrical box, with between 2 and 6 feet of cable between them (depending on which machine one is looking at - one is a Sieg X3 benchtop mill conversion, the other is a Shizouka AN-S CNC knee mill from the 1970s that's about 7 feet tall).
For this purpose, I designed two styles of breakout board (they use a pinout very similar to what a RAMPS uses; so modifying my grbl version to support it was a minimal effort). These were the PCBs that I mentioned had arrived, in the other issue on hooking up the Chinese spindle with 0-10v PWM drive.
One of them has places on the board for 5mm pitch screw terminals; and the other has a 26 pin header with a pinout intended to match the pinout of a GeckoDrive G540... which is what I'm going to be using to remotely locate the GeckoDrives from the Arduino.
The signal flow goes something like this:
Arduino --> Breakout Board --> 26 pin header to Parallel Port adapter (1) --> Shielded DB25 cable --> DB25 Breakout Board (2) --> G203V drives.
(1) : This is a standard PC cable for connecting the parallel port header on the motherboard to a DB25 socket on the back of the case. I used it because it's convenient and readily available. (2) : This is a standard breakout board sourced from eBay. I'm using it because I'm using G203V drives, not an actual G540. People who have a G540 wouldn't need this; the shielded parallel port cable would plug directly into the G540.
The G203V drives have optoisolated inputs; and thus the signals are current-mode; not voltage-mode. Among other things, this helps with reflections and noise. It looks from that photo that your drives are also optoisolated? If so, that will help significantly.
I guess best solution would be to have 2 Arduinos
The problem with having two Arduino's connected like that is the same problem with having a PC streaming over the serial port - synchronization and latency. It could be the placebo effect, but I can feel the difference in responsiveness between having the jog encoder wheel's ISR turned on, and having it revert to polling. My experience with trying to do jogging over the serial port was even worse... for that matter, I'm also not terribly fond of these new 'all-graphics' front ends on dedicated CNC controls (Hass, etc), compared to the old character-based displays - they have noticeable update lag that the old ones just didn't have.
This is not necessarily an insurmountable issue; however it is a non-trivial one. One possibility might be to leverage the ethernet physical layer; but run a protocol specifically designed for this (one does not need address fields in the frames, and there's no need for collision handling; for example). In any case, substantial custom hardware would be needed.
Saur0o0n
This is more like question/idea to consider.
After some successful testing (still on Uno yet) I try now to arrange my controlling stuff and power supply distribution to find proper casing for it. You can see the picture just as reference. Anyway this is going to be big (there is no actual 48V - 30A power supply on picture), so I would like to have it somewhere hidden from all the dust/scraps. But here comes the problem with DRO - it's pointless to locate it in hidden place.
I started to think how I could separate LCD, keypad, wheel - to make it movable and somewhere more accessible then the rest of the stuff. The best solution would be to have a small box with just those parts and long wire. But here comes another the problem, I could have a long wire for LCD, wheel and keypad and Arduino inside the "big box" with all the other components, or send all the controls to spindle and motors over the long wire and have Arduino in small box with LCD. I don't like the second idea, and frankly the first one is also awkward because of 24 wires required and I don't know how it will react for all interferences.
I guess best solution would be to have 2 Arduinos - one for CNC control, another just for DRO and create some communication channel between them. I know this would change the project quite heavily - but I guess I'm not going be the only one that will face this problem.
What do you think?