Building A Linear Motor


We admit that this project doesn’t have very many details available, but it was just too neat for us to pass up. It’s a small linear motor which [ligonapProduktion] built after seeing a very brief description of a commercially available version.

The video after the break shows him testing the motor. In this screenshot he’s holding the center shaft while the coil assembly moves back and forth. But it works with a stationary coil moving the rod as well. The motor is basically a modified solenoid. There are sixteen neodymium magnets inside the shaft. The set of four coils is driven by an ATtiny44. Just like a stepper motor, energizing the coils in the correct order pushes against the rare earth magnets creating motion.

We’re not sure if he has any use in mind for this build. For us we just like to see the concept in practice (we feel the same way about a homopolar motor build).

[via Reddit]

23 thoughts on “Building A Linear Motor

    1. The regular actuators are bistable or made monostable by building in a spring. What this person did was introduce stepped linear movement, I can’t remember ever seeing that feature in this form.

      I think there are people/developers waiting for this kind of setup. E.g. (miniature) robotics often uses linear controlled motion but they use (stepper) motors and transform that rotation to linear motion – which makes the design clunky.

  1. I actually use one of these in my day job! The real, industrial version. They are quite strong and accurate, and there is a significant air gap between the drive bar and the coil housing, so it’s good for dirty environments.

  2. I’d think the rod is actually a tube holding the magnets. Controlling could be identical to unipolar or bipolar stepper motors (I’d guess this is unipolar, since it’s using 4 coils). I think most industrial versions are actually 3-fase systems, and are controlled like 3-phase permanent magnet motors (with block or sine wave commutation), and with or without hall sensors.

    The video clearly shows the difficulties you get when most friction and thus mechanical dampening is lost; it becomes a mass and spring system which is insanely difficult to stabilise with closed loop systems.

    1. actually i only see 2 connections being made at the pcb end not 3 or 4 so this tells us that this for coils are lined up in series so you’re left with the very top wire bring it down to meet with the bottom wire and this two is what gets connected to the pcb.

      tho we do notice a bigger pcb with 6 connections so even doing the math 2×4=8 tho we only see 6 connections so im not sure whats going on here but each coil should have one+ and one- and there’s 4 total so that should be 8 wires for each setup but we see 6ports on the pcb so im lost

    1. smoothness would be the thickness of the magnets.. thinner magnets means the coils can align to a tighter width.. though this then means that the coils have to be thinner.. though the flip side of this is sorta microstepping the motor and driving two coils like you say.. there must be a most efficient method.. *cue experiments*

  3. Think about a giant “mobile” version lifting almost everything up for example a light pole, the necessary current might be mind blowing, not shure if harmonics will interfere with other devices (if you just use the amplified GPIO outputs of an uC)

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