# Design suggestions for Mechanical rotating disc with 30 degrees step

I am a software engineer with no knowledge of mechanical engineering. I need to buy or build a rotating disc which can rotate in 30 degree steps only i.e each time I try to rotate it, it should take a 30 degree step and stay fixed in that place. Hope it makes sense.

Searching on Google I could find only info about electrical rotary encoders. Unable to figure out how to search for mechanical devices I need.

My guess is these sort of devices must already exists. Can please share any info you may have on this and provide suggestions on buying or building this.

Update: As shown in above pic, on the surface of the disc, there would be LEDs of different color, spaced about 30 degrees apart (or 45 degrees). Each time I want to point one specific light to the sensor. So from time to time, I want to manually rotate the disc to make the required led point towards the sensor (i.e some led pointed exactly to sensor and no intermediate position) and be it locked there.

• Check out machining or lathe heads - they do indexing. – Solar Mike Feb 4 '20 at 18:19
• Are you talking about a disk on a detented shaft or a shaft that can -only- turn 30 degrees per impulse? What are you rotating it with? What is its function? Is the disk even attached to a shaft? So many questions, so few answers... – BobT Feb 4 '20 at 21:12
• So... You try to twist the disc, and it moves 30 degrees before getting stuck, but if you let go of the pressure, it releases, and the next time you twist it it moves 30 more degrees? Sounds like a seatbelt mechanism with a really low preload... – Jonathan R Swift Feb 4 '20 at 21:57
• Search for star wheel They turn and lock. The indexing move takes about 1/2 the turn of the driver, and the rest of the time the follower is locked. – Phil Sweet Feb 4 '20 at 22:57
• Also called a Geneva drive – Phil Sweet Feb 4 '20 at 22:59

Your question may be closed due to being rather vague and open-ended.

Your goal can be accomplished with stepper motors and appropriate controllers, with servo motors and controllers, and is also likely with a strictly mechanical approach.

Consider to edit your question to reflect a more detailed methodology. If you do not require automation, indexing mechanisms are common.

I did a quick search for indexers but found the best results on Thingiverse, an online repository for 3D printed models. One of the models I found was somewhat more complex than expected, a scroll cam indexer.

The YouTube has a one minute video of one such device, which rotates 60° for each turn of the driving shaft. The one I found on Thingiverse appears to have eight pins, for 45° movement per rotation.

Unfortunately, the Thingiverse entry does not provide source files, which would allow one to modify the parameters to achieve your desired rotation. The concept is clear, however.

In the non-3D world, there are a few images for scroll cam indexers:

One could extrapolate from the above image that a suitably sized worm gear assembly could provide what you require. The input worm gear would have to turn many times to make a 30° rotation, but the worm gear could be driven by a set of gears to increase the single crank turn to that required of your structure.

This images shows what is described as a 24 to 1 reduction assembly. One turn of the crank gives you 1/24th of a rotation, while you need 1/12th for your objective. This means the input shaft need have only a 2:1 increase.

Such a design is relatively mechanically simply, if it meets your unstated restrictions.