Comment on Why do we still use stepper motors?
Eranziel@lemmy.world 10 months agoI disagree with all your points. What kind of servos are you talking about?
BLDC and AC servos maintain full torque at stop too, and have about 2-3× the torque of a stepper of similar size.
The only way a stepper can rival a servo for precision is with a high degree of microstepping, which is far from guaranteed positioning with open loop control.
I haven’t directly compared response time between steppers and servos, but I would be extremely surprised if there’s a significant enough difference to worry about. Most servo-controlled machines are larger and so are designed to accelerate slower than a printer, if that’s what you mean. This is intentional because inertia is a thing you have to worry about, not because the servo reacts to command changes slowly.
There are valid reasons steppers are used on printers, but it’s not because they have superior performance.
KingRandomGuy@lemmy.world 10 months ago
Huh, this is true about BLDCs as well? I remember seeing in a video that BLDCs tend to have very poor torque output when stopped and especially when at low speeds, whereas AC motors have a pretty much flat torque curve until they get fairly fast. I’d be interested to know if this is true.
Eranziel@lemmy.world 10 months ago
That sounds like a problem from using too small of a drive. Every torque curve I’ve seen for brushless DC or AC servos is constant torque from 0 to about 75% rated RPM, and then starts to drop off.
KingRandomGuy@lemmy.world 10 months ago
That sounds about right. You can technically achieve full torque at 0 RPM, but the current required for that might be very high (and may not be practical for the small size, power limits, and cost of a 3D printer). I know this is a probably in Asian import mini-lathes - if you run the spindle too slow you won’t get much torque out because the driver can’t supply enough current.