Well, that’s why you use a proper servo drive. Yes, technically they oscillate at standstill, but it’s so little it literally does not matter. Closed loop servo control is a solved problem unless you’re trying to implement it yourself.
Well, that’s why you use a proper servo drive. Yes, technically they oscillate at standstill, but it’s so little it literally does not matter. Closed loop servo control is a solved problem unless you’re trying to implement it yourself.
I 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.
Cost is the short version, yes.
I don’t know what kind of servos everyone here is talking about that are less precise than open loop steppers. Low quality hobbyist stuff, I guess? Proper servo motors & drives are the standard for good reason for robotics, industrial CNC machines, and pretty much everything else that needs powerful motors with high precision. Much higher power density, higher RPM (good for increasing torque with a gearbox), equivalent or better precision, plus closed loop control is a huge capability and safety gain.
That said, good, industrial quality servo motors are 1) expensive and 2) aren’t made in small enough sizes to be comparable to the steppers on most 3D printers. Even the smallest industrial servo + drive I’ve seen is about 5x as big as the steppers on a personal 3D printer and costs $800ish. Obviously, both are deal breakers for a personal 3D printer.
3D printers are a fairly ideal application for steppers. The moving parts are small and light, meaning you both don’t need a large motor and the danger of slippage is lower. Plus, steppers are cheap.
Of course it’s not for fun. It’s for something more important than anything else - their bottom line.
You can very safely remove the “probably” from your first sentence.