Thoughts on hybrid stepper/servo motors?

Has anyone used the chinese hybrid steppers with on-the-motor encoders and drivers? I’m looking at making a fourth axis for my cnc mill, and considering trying out one of these. I have a typical early 2000’s build otherwise with discrete steppers being driven by gecko stepper motor drivers and I’m happy with it, but a rotary axis is a way to get myself in a lot of trouble if I lose steps. Servos and encoders back to the controller are obviously the best solution, but also a lot of work. So I’m thinking about trying one of the internally closed-loop steppers, and would love to know other opinions about them.

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Never used them but would be interested in the results :slight_smile:

@John_Bump I’m also looking at a 4th axis, and had the same concerns, so like @donkjr I’m interested in results.

Here are the closed loop servomotor alternatives I’ve looked at which led me to be interested in the closed loop hybrid steppers…

I have some Tarocco servos, but not enough torque for a 4th axis.

Servomotor

  • 5 A peak current at 24 V
  • 4000 rpm maximum angular speed
  • 3000 g·cm peak torque
  • 30 W peak power
  • 1440 counts per revolution optical encoder
  • 38 mm diameter, 5 mm shaft

3kg/cm torque at 24V. That’s about a ninth the torque of the NEMA23 steppers I have on my mill. I know that with closed loop I don’t need quite as much torque, but that’s weaker than I’d like for a 4th axis. (I was thinking of them for 3d printer.)

Incidentally, I was sad after getting the Tarocco that while the firmware was open source, it requires a proprietary toolchain on windows to rebuild:

Updating the firmware

Every Tarocco board comes with a bootloader already installed. You can reprogram it using just a USB to serial converter. You’ll need to download and install PsoC creator for Windows.

It looks like ODrive is substantially more capable than the Tarocco. And costs more too.

It looks like the closed loop steppers have really dropped in price. I am seeing some for $50, though not shipped at that price. Looks like $75-90 or so shipped for a single complete set on aliexpress from many vendors.

This does make me think a separate driver might be a better idea. Although, I build quadrature encoder boards. How hard would it be to roll my own around a gecko, with a microcontroller reading the quadrature output of a magnetic rotary encoder? Hmmm.

Huh, I was thinking the opposite, that the plummeting prices on closed-loop hybrid steppers made them make a lot more sense for many purposes than servos. I was just recording how I got here; when I first started looking at closed-loop systems the hybrid steppers were substantially more expensive.

ODrive has 8192 CPR capacitive encoders for $39 — that seems like a pretty good value to me.

It occurs to me that SwissMak — roundly criticized by machinists for building from an aluminum frame that will ring, and last I heard not yet delivered while continuing to ask for more money from backers — reported good 4th axis performance with an ODrive for the spindle. While I wouldn’t buy an aluminum-frame mill, I won’t throw the baby out with the bathwather; 2200W spindle with 8192 CPR encoder and a controller to match seems like it could work well.

I used to sell fairly large quantities of breakout boards for the Austrian Microsystems AS5045, which will produce 4096 cpr via SPI and costs about $7. The current revision of the chip also provides quadrature output, which is nice for an interrupt-based controller. I believe they now have some 16384cpr chips. They do take some somewhat fussy alignment to get set up, but they have reasonable hardware for giving you feedback on the setup alignment process, and if you can rigidly mount everything, you can burn the alignment information into PROM on the chip.

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