This is my first robotics experience, outside of one class 10 years ago. I've been Googling this question for about an hour but I can't find an answer!

I'm using a ROHS Step Motor 28BYJ-48 (with an Arduino Uno). The rotating shaft that sticks out of the step motor seems to be called a "double-flat drive". It's less than 1/4" wide, and is flattened on two sides.

stepper motor

I need to attach a 6" long arm to it, so the arm can spin like the second hand on a wall clock, but in both directions. What can I use to attach the arm securely to the shaft? What's the name of the part that will couple this double-flat drive shaft to a straight, flat piece at a right angle to it? Or are there flat metal circles with holes in them that can be coupled to the double-flat drive shaft without slipping - and what's the Google search phrase I should use to find them?


1 Answer 1


You can use a D or Double D shaped shaft collar/coupler. Or obtain a Double D shaped punch, depending on the design of the piece you are attaching to the shaft.

  • $\begingroup$ Thanks SteveO. The collar/coupler seems simplest to me, since the arm I'm attaching is a 1/2" square wooden dowel. However, the collars I've found online (Ruland, Amazon) seem to just create a cylindrical hole when attached to the shaft. How does the arm then get attached at a right angle to the collar/coupler? Or am I looking at the wrong kinds of collars/couplers? $\endgroup$ Commented Feb 24, 2019 at 19:30
  • $\begingroup$ A ser screw could work, but you have to make sure it doesn’t back out. You can find D shaped couplers, such as this: robotshop.com/en/0770-set-screw-d-hub-6mm-bore.html $\endgroup$
    – SteveO
    Commented Feb 24, 2019 at 19:40
  • $\begingroup$ Looks like a "mounting hub" is what I might need! Thanks for the guidance. $\endgroup$ Commented Feb 24, 2019 at 19:46

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