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linear steppers are rare

A project log for linear stepper motor 3d printer

Eliminate belts, pulleys, leadscrews.

DeepSOICDeepSOIC 03/25/2016 at 17:153 Comments

Quick browse through ebay and aliexpress didn't return any easily obtainable linear stepper motor. So building my own sounds like a good idea.

Discussions

absinthdraco wrote 03/25/2016 at 18:13 point

I've looked into this a little bit. For the passive portion I understand that you can go with either machined metal (specifically, with ridges cut into it to form teeth: for 1D the ridges are all parallel, for 2D the ridges form a right-angle grid), or or small pieces of metal placed together (alternating heights, to produce the same effect as the machined version).

For the active bit, you're looking at the same basic arrangement (a bunch of solenoids, oriented in parallel, arranged either linearly, or in a grid, depending on whether you're going for 1D or 2D).

Try to get the spacing of the active component and the passive component to be very precisely different from each other: it should provide a bit more accuracy. If you can make the passive portion have much finer resolution, then do your best to make your active portion be ((number of solenoids * passive teeth per solenoid) + 1 passive tooth) in size (a vernier scale, in essence), for the sake of accuracy.

If the linear stepper tends to slip, then try sticking a passive toothed array to each solenoid as well: concentrating the field may reduce slippage. Also bear in mind that without measurements, you won't have a clue what the exerted force of your linear stepper is, so you may need to find a way to increase force or decrease needed force.

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DeepSOIC wrote 03/25/2016 at 18:55 point

I hope to get some racks (those linear rails with trapezoidal teeth, that are supposed to mesh with a gear). I think they will be a rather good pieces for making the motor.

Alternatively, I can try to achieve something with a threaded rod, and nuts with same pith but larger diameter thread.

I am slowly thinking on the simplest way to make the motor, preferably without machining metal.

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absinthdraco wrote 03/25/2016 at 19:12 point

Racks could work, I guess. I believe I was originally thinking about arbitrary lengths and full-custom fabrication.

One of the upsides to the second way I described making the teeth is that it should be achievable with a dremel, and bar-stock: the only thing you would need to build is a tool to hold the bar stock and guide the dremel, for consistent sizing. If you want to make it slightly more professional, then encase it inside some U-channel or L-channel.

Depending on material and supplier, the bar stock might be more expensive than you'd like, but I suspect it would be cheaper than getting it machined, and possibly cheaper than a rack gear.

If I was going for threaded rod, then I don't think I'd use nuts: I'd use another piece of threaded rod instead. The reason is that I'm not certain if you'd be able to get internal threading to concentrate the magnetic field or not. Also, check the threaded rod to see how it interacts with magnetic fields: if it isn't ferromagnetic then you'll probable need to treat it like a maglev system instead of a stepper motor (maglev active arrays are built like linear steppers, but the operating characteristics are different: their operative concept is AC for movement instead of DC for position).

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