3 ms·

I feel like there's a gap in the hobbiest motor market. On the one hand there are stepper motors which can withstand lots of radial load thanks to steel shafts

I feel like there's a gap in the hobbiest motor market. On the one hand there are stepper motors which can withstand lots of radial load thanks to steel shafts and bearings. They also provide some relative position control and no absolute position feedback (at hobbiest prices). On the other there are servos, which typically have weak components. Plastic gears, shafts and bushings which cannot withstand radial load. But they do allow control of absolute position. For many robotics projects, a hobbiest has to choose between servos which are physically weak, or steppers which can tear the project apart if they don't home correctly. And of course the hobbiest has to roll their own safety/endstop system every time. I'd love something physically like a Nema 14/17 stepper but with a servo interface. However I can't find them anywhere at hobbiest prices. Why are there thousands of good value steppers and thousands of models of servos, but nothing in between, I wonder?

jbay808 4y ago
It's worth distinguishing between two completely different types of "servos": RC hobby servos, and industrial-type servos which are robustly built like steppers but significantly more fast, accurate, efficient, and powerful. They are hard to find in Nema 14/17 sizes but not impossible. RC servos typically have an analog or PWM signal interface. That would usually not be accurate enough for an industrial servo in positioning mode. Industrial servos, like steppers, have a digital interface which might be a serial format or STEP/DIR pulse train. Some drives will accept a -10V to +10V analog signal for velocity or torque control mode. Anyway, here are some Nema 14/17-sized industrial servos with online pricing, which might be what you're looking for? https://en.nanotec.com/products/2262-smart-servos-motors-with-controller-drive https://en.nanotec.com/products/2262-smart-servos-motors-wit... https://catalog.orientalmotor.com/viewitems/l-categories-servo-motors-tuning-free-servo-motors/50w-nx-series-servo-motors https://catalog.orientalmotor.com/viewitems/l-categories-ser... Or many companies offer stepper motors with built-in encoders and controllers to prevent missed steps: https://catalog.orientalmotor.com/viewitems/az-series-absolute-encoder-servo-motor/az-series-42mm-absolute-encoder-stepper-motors-ac https://catalog.orientalmotor.com/viewitems/az-series-absolu... https://www.zaber.com/products/stepper-motors/X-NMS-E https://www.zaber.com/products/stepper-motors/X-NMS-E
- gwynplaine 4y ago
  Thanks, lots of helpful links there. Much appreciated. Although quickly checking, I suspect they could be over an order of magnitude more expensive than the hobbiest equivalents.
  - fest 4y ago
    Somewhere between 1 and 2 orders of magnitude more expensive though not without a reason- increased demands for design, manufacturing, testing, reliability and having to support the product for several decades costs money. The cheapest of RC servos have a lifetime of a couple hundred hours max, even at less than half of their max torque (if their manufacturers would even specify what is the rated torque). I have one fail after two days of operation with a full rotation every 15 seconds with very light load. There are of course properly built RC servos- with serial communication for feedback, metal gearbox, brushless motor- but those start at ~50EUR-100EUR. IMO the best bet for hobbyist is NEMA17/14 motor with a driver that has rotary magnetic encoder on them- there are cheap and open source options for that. Next best thing would probably be a BLDC motor (optionally- geared) with SimpleFOC.
sbierwagen 4y ago
>However I can't find them anywhere at hobbiest prices. Might put this higher up in your comment. Dynamixel robotics servos exist, but at Dynamixel prices. Weird stuff has weird prices. If anyone made a useful home robot that sold millions of units then robotics servos would get rapidly cheaper, but that hasn't happened yet.
- HeyLaughingBoy 4y ago
  This is an important point. The low prices of a lot of hobbyist-grade motors and motor controls are driven by their use in consumer electronics. I can buy an entire 4-axis stepper motor controller with drivers for under $100 because they are made by the thousands for laser cutters and 3D printers. OTOH a similar professional controller will set me back at least a few hundred $$, if not a few thousand due to being designed for a harsher environment and for higher reliability.
- relaxing 4y ago
  iRobot has sold millions of Roombas. Wonder if there's been any economy of scale bleed-over from that work.
  - sbierwagen 4y ago
    Roombas don't use any servos. Just a couple of regular brushed DC motors. They do sell a blank chassis for classroom stuff: https://edu.irobot.com/what-we-offer/create3 https://edu.irobot.com/what-we-offer/create3

jbay808 4y ago

It's worth distinguishing between two completely different types of "servos": RC hobby servos, and industrial-type servos which are robustly built like steppers but significantly more fast, accurate, efficient, and powerful. They are hard to find in Nema 14/17 sizes but not impossible. RC servos typically have an analog or PWM signal interface. That would usually not be accurate enough for an industrial servo in positioning mode. Industrial servos, like steppers, have a digital interface which might be a serial format or STEP/DIR pulse train. Some drives will accept a -10V to +10V analog signal for velocity or torque control mode. Anyway, here are some Nema 14/17-sized industrial servos with online pricing, which might be what you're looking for? https://en.nanotec.com/products/2262-smart-servos-motors-with-controller-drive https://en.nanotec.com/products/2262-smart-servos-motors-wit... https://catalog.orientalmotor.com/viewitems/l-categories-servo-motors-tuning-free-servo-motors/50w-nx-series-servo-motors https://catalog.orientalmotor.com/viewitems/l-categories-ser... Or many companies offer stepper motors with built-in encoders and controllers to prevent missed steps: https://catalog.orientalmotor.com/viewitems/az-series-absolute-encoder-servo-motor/az-series-42mm-absolute-encoder-stepper-motors-ac https://catalog.orientalmotor.com/viewitems/az-series-absolu... https://www.zaber.com/products/stepper-motors/X-NMS-E https://www.zaber.com/products/stepper-motors/X-NMS-E

gwynplaine 4y ago
Thanks, lots of helpful links there. Much appreciated. Although quickly checking, I suspect they could be over an order of magnitude more expensive than the hobbiest equivalents.
- fest 4y ago
  Somewhere between 1 and 2 orders of magnitude more expensive though not without a reason- increased demands for design, manufacturing, testing, reliability and having to support the product for several decades costs money. The cheapest of RC servos have a lifetime of a couple hundred hours max, even at less than half of their max torque (if their manufacturers would even specify what is the rated torque). I have one fail after two days of operation with a full rotation every 15 seconds with very light load. There are of course properly built RC servos- with serial communication for feedback, metal gearbox, brushless motor- but those start at ~50EUR-100EUR. IMO the best bet for hobbyist is NEMA17/14 motor with a driver that has rotary magnetic encoder on them- there are cheap and open source options for that. Next best thing would probably be a BLDC motor (optionally- geared) with SimpleFOC.

sbierwagen 4y ago

>However I can't find them anywhere at hobbiest prices. Might put this higher up in your comment. Dynamixel robotics servos exist, but at Dynamixel prices. Weird stuff has weird prices. If anyone made a useful home robot that sold millions of units then robotics servos would get rapidly cheaper, but that hasn't happened yet.

HeyLaughingBoy 4y ago
This is an important point. The low prices of a lot of hobbyist-grade motors and motor controls are driven by their use in consumer electronics. I can buy an entire 4-axis stepper motor controller with drivers for under $100 because they are made by the thousands for laser cutters and 3D printers. OTOH a similar professional controller will set me back at least a few hundred $$, if not a few thousand due to being designed for a harsher environment and for higher reliability.
relaxing 4y ago
iRobot has sold millions of Roombas. Wonder if there's been any economy of scale bleed-over from that work.
- sbierwagen 4y ago
  Roombas don't use any servos. Just a couple of regular brushed DC motors. They do sell a blank chassis for classroom stuff: https://edu.irobot.com/what-we-offer/create3 https://edu.irobot.com/what-we-offer/create3