Originally Posted by
Neale
One important thing to look for (and the cheaper stepper motors available online often fail this criterion) is inductance. High inductance may give high torque, but it slows the rate of rise of current through the motor coils which means that the rate of torque increase is also slower. That means that they are OK at slower speeds but with higher speeds/faster pulse rates, the torque drops off. The motors I'm using are 8-wire so that the coils can be wired in series or parallel. Series means lower current but poorer high-speed performance; parallel means higher current draw but better high-speed performance. This is all a bit of a simplification but it's broadly true and why you don't want high-inductance motors if you want to run fast. Does mean bigger PSU and drivers to suit the higher current.
I'm using the Zapp 3Nm NEMA23 motors on a 1500x750 cutting area router. Fairly heavy gantry (maybe 75kg?) driven by two motors and 5mm pitch ballscrews. I'm limited to about 5000mm/min by whip in the ballscrews (I should have used 10mm pitch) but those motors seem to drive that load without problem. I'm also using EM806 drives (from Zapp). I wanted newer digital drives, even though I had some appropriate rating older analogue drives from the Mk1 router, because, apart from generally better performance, they have stall detection. With a dual-motor master/slave axis drive on X, you really, really, don't want one motor to stall while the other keeps running. That could get very messy. I have wired the fault detect signal from the drives back to my motion controller so that if one drive trips, the machine stops very quickly. While setting up and tuning, this happened a couple of times which gives me some reassurance that the system works. I run on about 68V and have wound the motor max current setting to a point that it seems to run reliably on load without overheating the motors. The EM806s are well within their ratings although I have a couple of fans blowing a gentle draught across them.
For motion control, I went for Mach3 and a CSMIO IP/M ethernet controller. It's probably about the best controller around (based on general feedback and reputation) unless you go for its big brother the IP/S which costs about twice as much. The IP/M is not the cheapest option, although once you add in the fact that with "lesser" motion controllers you also need a breakout board, and a decent one that includes spindle speed control is not cheap, it's not that bad. It also uses 24V for signalling which gives better noise and interference rejection compared with 5V systems, and has differential outputs to drive the stepper drivers - again, this is an unusual feature but gives better interference rejection. I fitted mine, wired it all up, and it just worked first time, no messing about. The down side is that the IP/M can drive a master-and-slave axis machine like mine, but it cannot properly home the two axes. In practice, I am finding that this is not a problem and I have a simple manual workaround for this. If I were starting again today (I bought the electronics a couple of years ago), I might consider the UCCNC UC300ETH instead which is a cheaper option and getting a fairly good write-up in forums like this one. Haven't played with one myself though. You can save money by not needing Mach3 and using the UCCNC software which is also getting good feedback. All the same, I'm pretty happy with what I have.
But there are as many opinions in this area as there are CNC builders, so take all my comments as one man's view!
Last Activity: 29-01-2024
Thanks for all the info.
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