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Sorry I am asking a mechanical question here, but, after all, where else people have experience with using motors? If there is a better forum for this, please do guide me.

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Everywhere I've seen online, the stepper motor 28BYJ-48 is used in tutorials, to rotate on its own, or, at most, to spin a clothes pin attached to it. I am trying to get Arduino to work for my 10 year old kid. He's got the motor rotating, now what? How does he attach anything to it?

Don't laugh, I made him a wheel out of a raw potato. He is happy with it now. Where can I find any guidance as to what to do next?

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  • $\begingroup$ Do you mean one of these: robocraft.ru/files/datasheet/28BYJ-48.pdf It looks like a 9mm diameter shaft with two flats. One technique is to get a plastic wheel with a smaller hole, and a very old, unloved soldering iron. Heat up the iron, push it into the hole, and while the plastic is hot, push it onto the shaft. Otherwise a wheel with a 9mm hole with two grub screws screwed against the flats might work. $\endgroup$
    – gbulmer
    Sep 25, 2014 at 19:51
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    $\begingroup$ +1 for "a wheel out of a raw potato" :-) and for your educational work with your kid! Projects with my dad is how I got started in electronics. What to do next? ... Find a way to preserve the potato. $\endgroup$
    – Tut
    Sep 25, 2014 at 19:55
  • $\begingroup$ @gbulmer, Yes, one of these. Thank you for your response, the word "shaft" along with the words "grub screw" (a.k.a. set screw apparently) got me some much needed search results. $\endgroup$
    – Ruby
    Sep 25, 2014 at 19:58
  • $\begingroup$ Where can I buy the parts I need? Both on- and offline $\endgroup$
    – Ruby
    Sep 25, 2014 at 19:59
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    $\begingroup$ Would polymorph do? $\endgroup$
    – venny
    Sep 25, 2014 at 20:10

7 Answers 7

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You can drill a hole to match the shaft into whatever it is and either fix it with a setscrew against the flat or glue it. Or you could glue a brass tube (hobby shop) to the shaft if you can find one that fits. The shaft is 5mm diameter, as venny says.

Of course it's easier if you have access to a small lathe (such as Sherline or one of the small Chinese ones).

If you need to allow for misalignment between shafts it's better to buy or make a shaft coupler such as these helical style ones:

http://www.ebay.com/itm/Flexible-Coupling-Motor-Shaft-Coupler-3mm-X-5mm-/220977869760

There are other types (some of which have a bit of backlash). You can also use a collar with setscrews, but the shaft on that motor is a bit stubby and that type of coupler allows for almost no shaft misalignment so it would jam easily (and the motor is not very powerful). The kind with backlash generally has a bit of flexible material such as urethane rubber sandwiched between two interlocking sets of fingers.

I made a sky tracking drive using one of these cr*p motors and I just drilled out the center of a standard gear (from Stock Drive) a bit to get a slip fit and used the grub screw to secure it. The shaft is pretty stubby so it's hard to get something secured to it unless it fits very tightly or is a clamp or collet-style fixing. In my case, the gear drives a nut that works on a leadscrew.

BTW, you might find the robotics SE useful in this kind of thing. I've not looked at it once, but those folks run into this sort of thing regularly.

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The diameter of the shaft is 5mm, it sould be possible to use a 5mm propeller collet commonly used on RC airplanes, like this one:

pic
(source: hobbyexpress.com)

Tightening the nut secures the attached object and at the same time it clamps the collet to the shaft.

The shaft should be inserted fully into the clamp, to grip also the non-flattened portion to provide good stability.

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I found, that carefully filing the shaft down to 2mm will make it a perfect fit for lego gears. You will have to file the flat sides. You can check uniformity of your work by light reflection. The shaft indentation in the front works as center guide, so you take off from both sides evenly. You also might have to slightly round the edges.

If you don't like that, try an adapter: check whether your local library has a 3d printer (some are setting up science labs for kids). There are a handful adapters for this motor (lego, round axis, servo,..) which you can download and print on a 3d printer.

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From RobotShop.com

You can use the Actobotics 5mm Bore 0.77'' Set Screw Hub

Given that part, you then have lots of options.

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As others have already stated, the shaft in a 28byj-48 is a "5mm diameter round shaft with 2 drive flats".

(Just for reference, the shaft diameter on a 28BYJ-48 is the same as on Nema 11, Nema 14 and Nema 17 stepper motors in case you ever want to upgrade your stepper motor!)

One option that has already been suggested is to use a "5mm mounting hub" (also known as a "set screw hub"). Pololu make an "all-metric" item (both the mounting holes and the grub screw/set screw are metric.) (Web Archive link) You can buy these from ebay - in the UK, a pack of 2 is approximately 8 GBP.

An alternative is to look for a "5mm flange coupling". These are also available on ebay and start at approx 4 GBP. (I have just received mine and it's perfect for my project.)

28BYJ-48 with attached flange coupling

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It is amazing that there are so few solutions for power transfer for such a common motor. I have looked at ebay and amazon. Gears are available in a wide range of prices, none that are in the same scale as the price of this cheap motor. There is a gear generator at http://woodgears.ca/gear/help3/index.html for wood gears. This or 3d printing gives you the flexibility of gear ratios and shaft sizes. I just wanted to be able to connect a programmable motor to a drive that would actually do something.

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The simplest, most versatile, and cheapest method I found is explained in this ebay page.

Basically you can get a Lego Technic axle (part #6538), remove 2 thin flaps, and it fits perfect. This allows you to connect the DYJ48 stepper motor onto any Lego Technic wheel (there is a range of them), gear, or any other Lego Technic part.

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  • $\begingroup$ Originally suggested by formfeed. Due to my low reputation level, I am unable to comment his answer to add the link, so I decided to post another answer that might be able to help other people who get stuck in this same boat. $\endgroup$
    – UndergroundCoding
    Feb 5, 2018 at 20:49
  • $\begingroup$ Please don't use links to eBay pages. eBay Links rot very quickly and the pages are not archived, so answers which rely on them become useless when the eBay auction expires. If you add more context from the link, it is more likely that people will find your answer useful. $\endgroup$
    – Mark Booth
    Feb 6, 2018 at 11:23

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