View Full Version : Midweight steppers

06-02-2015, 07:17 PM
I've been sniffing around the CNCRP offerings, and the kits look very nice. I very much appreciate all the time you guys have put into documenting your experiences.

As you know, there's a quite significant price jump going up from the CNCRP NEMA 23 kit to the NEMA 34 kit ($685 to $1549, DIY versions), mostly because that gets you out of the Gecko G540 domain of simple, all-in-one stepper controllers.

Now that the Leadshine MX4660 (http://www.cncrouterparts.com/leadshine-mx4660-4-axis-stepper-driver-p-334.html) is available, I'm wondering if the ground hasn't kind of shifted as far as the appropriate default configuration. The MX4660 is a 4-channel controller plus BOB similar to the G540, but it supports (well, advertises, at least) 6A/phase as opposed to the G540's 3.5A. It's pretty new, but opinions of the 3-channel version, the MX3660, seem to be generally positive. So for just a few $100s more than the $685 baseline, it looks like you can possibly get into NEMA 34 territory without derailing into Chinese-electronics hell.

I was looking in particular at the SureStep STP-MTRH-34097 (http://www.automationdirect.com/static/specs/surestepmotors.pdf) motors, rated at 800 oz-in stall torque and 6.3A/phase, with inductance of 2.1mH. These run about $115 on eBay. Here is the torque curve:

I'm not really a torque curve connoisseur, but this looks pretty smooth and linear to me at 48V. If you compare with CNCRP's benchmark top end of 1200 imp rapids for their NEMA 34 system (and if my arithmetic is correct), that works out to about 8,200 half-pulses per second, where the SureStep motor still seems to be within its operating range. Of course, I wouldn't assume identical or even similar performance just based on this, but at least it seems to be in the same ballpark. (Of course, you'd derate by ~15% because of the MX4660's amperage limit and presumably optimistic specs.)

Just as a back-of-the-envelope calculation here, it looks like the price of admission is $359 for the MX4660, $115 x 4 for motors, $240 for a 48V, 21A power supply, and say $50 for cabling = $1109. Not bad, and certainly less of a hockey-stick uptick than per-channel Gecko drivers.

Any thoughts?

Would it be a better option to just go with CNCRP's NEMA 34 motors and run them at 6A rather than 7A? Unfortunately, I don't think there's a published torque curve for those motors. (I suspect they are custom-specced Wantais, based on the part numbers and appearance.)