It’s little secret that stepper motors are everywhere in FDM 3D printers, but there’s no real reason why you cannot take another type of DC motor like a brushless DC (BLDC) motor and use that instead. Interestingly, some printer manufacturers are now using BLDCs for places where the reduction in weight matters, such as in the tool head or extruder, but if a BLDC can be ‘stepped’ much like any stepper motor, then why prefer one over the other? This is the topic of a recent video by [Thomas Sanladerer], with the answer being mostly about cost, and ‘good enough’ solutions.
The referenced driving method of field-oriented control (FOC), which also goes by the name of vector control, is a VFD control method in which the controller can fairly precisely keep position much like a stepper motor, but without the relatively complex construction of a stepper motor. Another advantage is that FOC tends to use less power than alternatives.
Using a FOC controller with a BLDC is demonstrated in the video, which also covers the closed-loop nature of such a configuration, whereas a stepper motor is generally driven in an open-loop fashion. Ultimately the answer at this point is that while stepper motors are ‘good enough’ for tasks where their relatively large size and weight aren’t real issues, as BLDCs with FOC or similar becomes more economical, we may see things change there.
I’m surprised we haven’t seen brushed DC motors with position feedback like in consumer inkjet printers. Even with a dozen nylon gears, I would still expect it to be far cheaper than heavy steppers with drivers.
With brushed DC motors you can’t lock them by driving at specific current and voltage. You can do that with BLDC and especially with steppers. The one problem with steppers is that the holding torque drops with microstepping. At 1/16 steps you get 9.80% of nominal torque, and that drops to 4.91% with 32 microsteps. With 3D printing that’s not a big deal as the moving mass is quite small. But for CNC machines in which a spindle alone weights twice as much as even the heaviest extruder head, this creates a problem of loosing position. And once you loose a few steps, your work is ruined, and you can even break the milling bit because machine doesn’t know where it is and thus it can hit the part holder (which happened to me a few times).
That is why a brushed DC motor with position feedback comes in. You’re right, in itself the motor can’t be “locked in place”, but using a position control loop, this is perfectly possible, even without consuming current when it is not battling forces to stay in position (a stepper always consumes). It basically behaves like a hobby servo motor then.
The fun part comes when you use precision rotary encoders to accurately microstep stepper motors…
no HaD search results for S42B so far.. not quite precision encodee, but good-enough?
https://youtube.com/watch?v=eM8zSG8fEkk
Oh, you can do quite a bit finer. Excellent work by Diffraction Limited here https://youtu.be/MgQbPdiuUTw
Nice attempt but this video-bait still failed to attract my clicks.
Anon over here rationing out his clicks like foodstamps in the last week of the month.