Opto-isolated integrated closed loop stepper driver boards

[JW]

On my first machine I'm building now, I'm using closed loop steppers for X & Y, namely these.

For what it's worth, if it helps anybody - I'm using a Duet 3 Mini 5+, but these motors have opto-isolated differential inputs which require a good 10mA drive current through the optocoupler LEDs, much more than the Duet STEP/DIR/EN output pins can directly source or sink.

As such, I've had to build an expansion board to drive these, it just takes the STEP/DIR/EN inputs feeding a row of gate drivers, feeding a row of low side N FETs. Voltage source is selectable between the Duet's V_FUSED supply, and an externally supplied via the 2-pin Molex KK header supply.

It uses the same expansion header and mounting holes as the Duet 3 Expansion Mini 2+

If anybody needs the same, I've got several boards left over due to ordering MOQ, so can pop them up on eBay...

[dc42]

Nice work! We've had it mind to produce a similar board for driving opto-isolated external drivers, but haven't got round to it yet. To this end we provide 5V on that connector. We've learned that some drivers (notably Clearpath ones) prefer active pullup, so our preferred way of driving external motor drivers needing 5v signals is now to use 74ACT04 buffers.

[JW]

Thanks!

Are these the Clearpath motors you refer to? I've not come across them before, I've used Schneider Lexium servos before, but never seen these. I'll take a look, as on machine V2 (the 'proper' machine), I plan to use servos with robust screw thread connectors etc rather than the typical JST/Molex type connections on entry level steppers.

The Clearpath motors look like a very nice package!

Makes sense using the hex inverters for such motors.

I'm not sure on the Duet policy around contributions to the open-hardware side of the project, but when I find some more time available I'm happy to complete the documentation and contribute the design to the hardware repository, it's only a very small contribution but if it helps somebody out...

Need to add a diode first after the jumper, before the KK - as it's currently possible to essentially feed V_FUSED with a secondary supply through that KK, if the jumper remains connected and a supply >V_FUSED is present on that KK, which was very much not the intention.

Equally BOM needs a re-visit as it currently uses all AEC-Q100 qualified parts that we had in stock so not particularly cost effective given the application.

If there are any hardware guidelines required for contributions, and the project would see value in it, please let me know.

[Wayne Black]

I ran the CP SDSK motors on a 3axis machine. The 72v power supply and in situ motor tuning worked very well. One thing I couldn't stand about them was the ridiculous signal/controller cabling. Its large gauge conductors with mini molex connectors make no sense to me. I made a mini molex to rj45 breakout for the controller board and the motor. It worked ok, but the mini molex connectors are wire to wire only. I couldn't find a proper header for them so I made a motor 'dongle'. It was kinda hacky, but made cable management so much nicer.

In the end the CP SDSK motors are sitting in a box and I use cheap chinese close loops like the one you posted. For my CNC I use yasakawa ac servos, they perform excellently and relatively inexpensive.

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Wayne Black

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[JW]

Looks like these days they do an M12 connector option, which is miles nicer than cheap Molex connectors as you say.

[dc42]

BTW Duet3D sells Nema 23 closed loop stepper motors now, see https://www.duet3d.com/duet3motor23cl. These connect directly to the CAN-FD bus of any Duet 3 main board.

[JW]

Interesting, are there a torque/speed curves available for this motors?