# What mechanism can make a wheel turn in discrete steps?

I want to make a wheel that behaves pretty much like a mouse wheel does — when you rotate it with your finger and release, it rotates back or forward by itself to match a nearest discrete position.

What are the common ways to do so?

• I think what you're asking about is a "detent" en.wikipedia.org/wiki/Detent: "a device used to mechanically resist or arrest the rotation of a wheel, axle, or spindle." Jan 4, 2018 at 2:36
• Detents are used in .. bicycle gear levers, the grind setting on my coffee bean grinder, the position in my windshield wiper speed setting knob, for a few examples. Jan 4, 2018 at 14:07
• Possible duplicate: engineering.stackexchange.com/q/13208/2559 Jan 4, 2018 at 16:51

One way to do this would be using permanent magnets arranged in a circle spaced out on a base plate with a central pivot point for a top plate (your said wheel) that has a ferrous disc mounted in it. Use the magnets with either pole facing up. As you rotate the wheel, the ferrous disc will be attracted to whichever magnet it is closest to, you can space the magnets to give you any detent pattern you like.

a stepper motor. they have discrete detents, furnish propulsion, are cheaply available in a variety of sizes, and easy to drive using arduino, raspberry pi, beaglebone, etc. and lots of user information regarding them exists in the robotics community.

• Thanks, but it doesn't really look like a thing I'm trying to find. What I'm really looking for is a mechanical wheel that you rotate with your actual finger to drive some mechanical fanciness (like the aforementioned mouse wheel or a wheel with digits on some bike locks) and which self-adjusts to some discrete steps. Jan 4, 2018 at 3:26
• got it, sorry. -NN Jan 4, 2018 at 5:12
• A stepper motor actually gives a nice tactile feeling when rotating the axle with your fingers and stops at distinct steps. Try salvaging from an old printer or CD ROM or something. It works similar to William Hird's answer, though the resolution may be too fine
– ChP
Apr 6, 2018 at 8:28

Genova or Geneva mechanism is stepper mechanism, there are plenty of websites explaining Geneva mechanism or drive, like this wikipedia article Geneva drive

• Hi Katarina, please add details as answers that rely on links suffer when the linked items dies - been guilty of this myself ! Jan 4, 2018 at 8:58
• @SolarMike it is well known mechanism he just needs to google it and he'll get nice 3D simulations and explanations. Jan 4, 2018 at 9:21
• A picture and a short para would be great though and you may find people voting for it... Jan 4, 2018 at 9:58