Hand crank to be used as a on switch for a system?

I'm looking to make a music box for a cosplay I would like to do/make. I know how to make a music box, but for the sake of ease and to make the music sound better, I would like to make it all electric. With that comes a new issue: I would like the music to only play when the crank shaft is being...well...cranked. Any idea?

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What you are looking for is a friction type switch where a "strap band" is tightened to a "slip fit" around a "drum". This drum is turned by the crank. Where the strap comes together, a metallic arm is mounted so that when the crank is turned, the drum rotates and the friction pulls the strap/metal arm against a contact that completes the circuit. In order to open the circuit when you stop turning the crank, use a light spring to pull the metal arm away from the contact point. Actually a simple concept, just needs some finesse to get it to work correctly. The coolest part about it? The look on people's faces when you tell them you made it yourself.

Qa

(+1 to Re-design)
DoctorWoo (author)  Quercus austrina5 years ago
That's actually a beautiful idea! I understand the concept, but I'm still a but etchy on the design and strap band principal.
I keep thinking of a slip ring and brush inside of a motor. Only, as you stated, with a strip of metal versus a brush.

I think what I;m driving at is I don't quite know how the strap band would come in contact with the drum. The rest makes perfect sense to me.
Thanks in advance for the answer(s)!
I have prepared an image so you may visualize how one works. Should there be a problem viewing it here, I have loaded it to my Postimage account.

Adjust the friction via the adjusting bolt. You want enough friction so that the arm touches the contact point when you turn the crank, but has enough "looseness" that the spring pulls it away when you stop turning the crank. You'll get the feel for what you need when you see it n action. 

You can change the direction of the switch by flipping the contact point and the stop. Additionally, you can make it bi-directional (switch closes no matter what the direction of rotation) by making the stop a contact point (you then have two, one above and one below the metal arm) and connecting that to the red wire, and add another spring opposite the one shown. If you want more positive contact with the black wire, you can clamp it to the metal arm under the leather at one of the rivets/bolts.

Hope this helps and you are successful in your build. Let us see how it turns out.

Qa
Directional Friction Switch momentary n o.png
"see it n action" should be "see it in action". So much for proofreading. We really could use an EDIT feature. I detest deleting and reposting.

Qa
DoctorWoo (author)  Quercus austrina5 years ago
An edit button would be handy. I'm not the greatest typer, and always make a few mistakes.

But back to the task at hand, that's a fantastic illustration and nailed everything I needed! Thank you kindly for the help!
+1
Thank you kindly, Kiteman.

Qa
DoctorWoo,

You are quite welcome. I enjoy helping people, especially with unique situations such as this. The sketch is nothing special, just a MSPaint quickie. You can customize the design to fit your needs, nothing is set in stone (that's why the "*NOT TO SCALE" notation).

I designed this taking cues from many really old mechanical devices such as the old leather belt and pulley power transfer systems from the dawn of the industrial age, strap wrenches (used to make them when I couldn't find my oil filter wrench) and old leather shock absorbers (yes, leather shock absorbers on a real vehicle, I just can't remember which one(s)). Something to be said about paying attention to history - you never know just when you'll need it. :)

Qa
My idea would open and close contacts many times a rev, and you could then adjust the playback speed......
Re-design5 years ago
A push buttone that the end of the crank push on when it is cranked.

Or

A ring on the crank axle that is friction controlled.  So that it pulls on a switch when the crank is turned.