Want to split off the drivers for CNC

(Phillip Hallam-Baker_SW) #1

I am currently trying to work out how to wire up my Shapeoko-2. This is a smallish CNC machine but has the option of swapping out the short rails supplied for much longer ones, 5 foot square cutting areas are common.

One of the big challenges to going bigger is cable management. At the moment I have the following lines in to each axis:

Stepper motor: 4 wires, up to 2.5 amps
Endstops: 2 sense wires + Ground (+ 3.3 V if using optical), negligible current.

The problem with the current setup is that I have to run 2 separate cables for each axis. I also need to make up a break out panel to interface the cables. Rewiring is a non-trivial affair.

Now one of the particular features of the Shapeoko is that it is a belt driven design. So if the limit switches are mounted on the motor carriage, the motor/switch geometry is fixed. All the electricals associated with one axis move together (neat!).

Unfortunately the carriages are not big enough to mount a smoothie board on or a standard stepper driver.

What I would really like to go to is the following:

Each axis has separate signal and power lines. The signal lines are run over CAT6 ethernet cable which is the cheapest source of wire. Only logic level signals go over this cable so there is no risk to equipment if there is a mis-wiring. This makes use of standard ethernet cables and connectors possible.

The power lines can then use standard 2 core cable of suitable gauge. This line can be daisy chained as the Z axis is mounted on the X axis. Just have to use a sufficiently thick gauge of wire.

Each axis would then have a small breakout board about an inch square with input connectors for power (24V) and signal (ethernet jack) and screw terminals for the motors and pin connectors for the end stops.

The stepper driver chip would then mount on the breakout board. This could be on the reverse of the board so that the chip can mount against the carriage aluminium and use it as a heatsink.

At the other end there would be another breakout board to split the signals out.

So does this make sense and has anyone seen something similar before?

Imported from wikidot

(Arthur Wolf) #2

I think what you want to do will be EMI hell.

You need to have the Smoothieboard static, the stepper motor drivers static ( you want as little moving mass as possible anyway ), and your endstops to have the shortest possible cables.

What can be long, is your stepper motor’s 4 wires. That’s fine. Just make sure you don’t run them too close to your endstop cables.

If I understand what you describe correctly, it is both un-necessarily complicated, and prone to high error rates due to EMI. Which is why professional machines don’t do it that way :slight_smile: