Sunday, 19 July 2009

$8 Z-axis

About a year ago I blogged an alternative Z-axis for Darwin using four tin can steppers instead of one expensive stepper and a belt drive. The only thing missing was a source of cheap motors to make it economically viable. Some time ago Forrest Higgs pointed out a source of cheap 15° motors for $2.50 made by Airpax. I also found them available for $2 at Surplus Shed. That makes a z-axis for $8 possible, which is much cheaper than original motor, let alone the belt.

They are surplus stock, so when they are gone they are gone, but there does seem to be a lot of them around. Unfortunately it costs more than $40 to ship them from the US, so the economics don't look nearly so good this side of the pond.

They are 12V 0.4A per coil, so four wired in parallel will take 1.6A, well withing the 2A capability of the RepRap electronics. They are six wire unipolar motors, but they can also be driven from a bipolar drive by using the red and orange wires as one coil and the green and brown as the other.

The pull in rate seems to be about 200pps, which would give 200 × 15 × 1.25 / 360 = ~10 mm/s with M8×1.25 threaded rod.

The boss on the back of the motor is a bit bigger than the motors I used before so I have updated the bracket design accordingly. The motors come with a spiral drive screw on the shaft. I could not find a way of getting it off, so I made a new coupling piece that clamps over it. It has a pointer so that it is visually obvious if the motors get out of step with each other.

I have uploaded both of these to Thingiverse. The other parts needed are shown below: -

And this is how they go together: -


  1. Very nice! The Z axis belt drive gave me a lot of trouble on my Darwin, and the gears are a bit beyond what we can print right now. This should simplify things a bit!

    A few relays and a touch sensor toolhead would allow you to level the bed automatically too, but that would add a fair amount of complexity.


  2. I've been following your blog for a long time. I've got a repstrap built with everything but wires between the motors and the boards, and I have a bits from bytes extruder which has been giving me some problems in terms of grip. It's nice to see you still have your project going. It's inspiration.

  3. I haven't really seen these about. Do they come in any specific type of machine I can target to scrounge? Or are they found some other way? I guess I should just stop being lazy and google them. Bleh.

    Nice post!

  4. I was impatiently waiting for your new blog posts! Finally, its here and everything is back to normal;)

    I will be able to use a lathe in september, I really hope, you will finalize the "one truth extruder design";)

    Anyway all I wanted to say is nice to see you around, your blogposts are my daily drugs;)


  5. Hi Demented,
    If you follow the link to Surplus Shed it is the page where they can be had for $2. I think they were over produced stock. They look like they are for very old 5.25" floppy disk drives. I have recovered similar ones from TRS80 disk drives, but they had a wheel with a spiral trcak rather than a cyclinder.

  6. Nice. I'll have to look into some of these. They look very beefy. I've got a bag and a half of random NEMA 17 and 23 steppers sitting around now from scavanging since starting on my RepRap but it would be great to get some for so cheap for other projects.

    Anyway, thanks for posting again. It's awesome to read your stuff.


  7. They don't have as nearly much torque as a NEMA23, but then they don't need to. The torque required from each motor is much less than 1/4 of the single motor design because the friction created by the belt is gone.

    I would think four NEMA17s would also do the job.

  8. I have 4 £12 Nema 17s that I'm making clamps for repstrap Darwin I struggled with the milk bottle top gears. Will post my results once I finish writing up my DIY version of the pinch wheel Extruder.. Started writing it over a month ago :-( not had much spare time since thou.

  9. Most excellent as always.