Why are 3D printers still stuck on stepper motors? Why haven’t we transitioned to servo motors with encoder feedback for positioning?

Is it just too cost prohibitive for the consumer-level? We would be able to print a lot faster and more accurately if we had position feedback on the axes. Instead we just rely blindly on the stepper not skipping any steps when we tell it to move, hoping for the best.

  • beeb@lemm.eeEnglish
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    10 months ago

    Have you seen how fast printers with stepper motors can get? They print benchies in less than 3 minutes. The bottleneck is not the motion system, it’s either the hot-end or the part cooling. Also stepper are super accurate and very flexible. Drivers are advanced and can tune for torque, speed, sound etc. Collision detection and skipped step detection is also a thing.

  • empireOfLove2@lemmy.dbzer0.comEnglish
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    10 months ago

    Stepper motors are considerably easier to lock in a single location than continuous rotation servos. When they are commanded to a certain position they will STAY THERE. This makes precise positioning considerably easier vs a continuous rotation servo, which must use a sensor feedback loop to ensure it stays close to where it needs to be. And any feedback loop will involve small amounts of extremely undesirable oscillation and movement about the target point…

    besides. we can already drive steppers significantly faster than any hot end can melt plastic.

  • Excrubulent@slrpnk.netEnglish
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    10 months ago

    Just to add on to this, I understand the technical benefits to steppers, but surely a stepper motor could be given some servo-like functionality by simply adding encoders to the stepper shafts. You can get rotational hall sensors with diametric magnets for a couple bucks each. Even if you weren’t using the encoders to operate the motors directly, you could use them for fault detection. An encoder with 10 bit accuracy could just about match the substeps of stepper motors for resolution.

    Now, most of the time when a stepper gets out of, well, step, it’s because something’s gone wrong and you wouldn’t necessarily want the printer to correct it directly, but simply being able to pause on a fault and record the fault’ time and direction would make a big difference to troubleshooting.

  • FuglyDuck@lemmy.worldEnglish
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    10 months ago

    In addition to the other points made… steppers maintain full torque even when it’s not moving, so it’s better at braking tool heads.

    Also? Steppers have a higher precision to a servos higher speed and torque (but torque that’s not constant.)

    Finally they have a better response time. This isn’t the speed, so much as the speed that control inputs are reflected. Imagine all the tiny wibbles a printer makes during infill, the changes in direction would be sloppier with a servo.

    • Eranziel@lemmy.worldEnglish
      0·
      10 months ago

      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.

      • KingRandomGuy@lemmy.worldEnglish
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        10 months ago

        BLDC and AC servos maintain full torque at stop too, and have about 2-3× the torque of a stepper of similar size.

        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 (due to very low efficiency requiring too high currents for drivers to supply), 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.

    • curiousPJ@lemmy.worldEnglish
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      10 months ago

      Steppers have a higher precision to a servos higher speed and torque (but torque that’s not constant.)

      Just trying to understand this. Then how come all CNC precision machines use a servo instead of a stepper? I mean there are some ridiculously accurate machines that can position itself over and over varying under a micron (<.001mm) but the manufacturers choose servo over stepper. Is it for the sake of holding torque that servos have to be used over steppers?

      • ShepherdPie@midwest.socialEnglish
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        10 months ago

        All the DIY CNC machines I’ve seen use larger stepper motors. The commercial CNC machines I’ve seen can cost $10,000 to hundreds of thousands.

        • curiousPJ@lemmy.worldEnglish
          0·
          10 months ago

          It seems like the argument is that at the lower price bracket, stepper motors offer higher performance than what a equivalently priced servo+encoder+controller combo can perform.

          I felt like what I was reading in this thread wasn’t matching up with that I see out in industry… concerns about ‘price’ didn’t come up until your post.

          Diamond turning machines are inherently low torque, low speed, AND nanoscale operations which uses servos for driving its respective axis. See precitech -youtube and in stark comparison Roeder’s 5axis optical mold machining. Wire EDM’s were all driven by servo motors until linear motors became popular. Even those famous JingDiao test samples are made on machines driven by servos.