Sunday, June 10, 2012

3-Axis A4988 Stepper Driver Carrier

More on the perpetually in-progress CNC (see the mechanical stuff in parts I, II, III, IV)

I've recently built a prototype board for the Pololu A4988 stepper drivers carriers.  These little drivers are inexpensive (about $12) and fairly gutsy (2A per phase), but can blow fairly easily.  Using male headers they can easily be used as drop in modules for a larger CNC controller board.  My board breaks out the microstepping pins to DIP switches and adds screw terminal connections for the high-power side, with female headers for the TTL control inputs and low-power supply.

The two-pin set of female headers on the left is the low-power supply, the middle six-pin set of headers is the step/direction controls for each of the axes and the bottom six-pin header is for upper and lower limit switches for each axis.  The top set of two-pin screw-terminals is the motor power-supply and the remaining 3x6 pin connectors are the motor winding connections with the bottom two terminals for upper and lower limit inputs.  Unfortunately I ran out of space on the board to provide a 5V supply to the limit switches, so these will have to be wired externally to 5V.  I may also add some pull-down resistors to the backside of the board, since the switches are currently floating, although this does not seem to be a problem in practice for some reason.

There's a surprising number of solder joints needed for this simple board, largely due to using point-to-point wiring, but it seems to be electrically sound:

This board really cleans up my testing rig for the CNC, just a few jumper wires are all that's needed to connect my Arduino to the two mostly-finished translation stages.  Using screw-terminals instead of soldered on connectors is also much more convenient when rewiring the steppers as bipolar parallel/serial during testing:

The final machine will probably not end up using this board, I'm considering investing in a proper 3-axis board, since they can be found quite cheaply on Ebay.  That said, it's a nice tidy little package that allows the stepper drivers to be replaced as needed as well as preventing the inevitable wiring mistakes that happen when developing on breadboards.

1 comment:

Shahabz Hussain said...

3-Axis A4988 Stepper Driver Carrier

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