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Mechanism with spiral spring

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An Mich Kotzelbaum25/02/2022 16:29:18
9 forum posts

Hi all,

for some of you this question will be trivial.

I would like to build a mechanism that i'd like to implement in a sort of "mono tone musical instrument" for my nephew.

Basically: i have a tuning fork mounted on a support and it should be hit by a hammer (or a stick..) by pushing a button. Now, the button should be "soft" to push, on the other hand the hit should be powerful enough to produce a loud tone.

I first thought at the classic boxing bell mechanism. It's fine, but it seems a bit hard to use.

Now i'm actually thinking at clock mechanisms. In this case there is a spiral spring that stores the energy. The idea of charging the whole thing by a knob or handle seems fun to me. Maybe it could provide for more than one hit

Does anybody know if there is already some mechanism like this, out there? If not, any ideas at all?

Thank you in advance for your feedback!

An Mich

Michael Gilligan25/02/2022 20:30:03
avatar
20182 forum posts
1053 photos

You might find inspiration here : **LINK**

http://507movements.com

… It’s fun to browse, anyway.

MichaelG.

pgk pgk25/02/2022 20:35:34
2563 forum posts
293 photos

A trigger release, such as found on crossbows - suggest a captive bolt wound or drawn back by hand. Similarly, could use the basis of an airgun cocking and trigger mechanism or for simplicity a simple hanging rod & weight that snaps into a release mechanism with a pull-string to reload. The problem with the above options is that the clapper will likely rest against the tuning fork and dampen it although with the pendulum version it could be arranged not to swing back far enough for a second strike.
Someone cleverer than myself could likely knock up a simple circuit so a single strike via a solenoid then reverses and resets - wouldn't even need a button push if using a break in a light path as the trigger - just a finger in a gap.

pgk

old mart25/02/2022 20:48:26
3775 forum posts
233 photos

How about the mechanism design similar to the bass drum pedal in a drum kit.

Martin Connelly26/02/2022 08:08:33
avatar
2137 forum posts
222 photos

Two tone door bells do this.

Martin C

An Mich Kotzelbaum26/02/2022 08:19:59
9 forum posts
Posted by Michael Gilligan on 25/02/2022 20:30:03:

You might find inspiration here : **LINK**

http://507movements.com

… It’s fun to browse, anyway.

MichaelG.

that's so cool!! Thank you, it is fun to watch indeed and instructive as well

An Mich Kotzelbaum26/02/2022 08:28:11
9 forum posts
Posted by pgk pgk on 25/02/2022 20:35:34:

A trigger release, such as found on crossbows - suggest a captive bolt wound or drawn back by hand. Similarly, could use the basis of an airgun cocking and trigger mechanism or for simplicity a simple hanging rod & weight that snaps into a release mechanism with a pull-string to reload. The problem with the above options is that the clapper will likely rest against the tuning fork and dampen it although with the pendulum version it could be arranged not to swing back far enough for a second strike.
Someone cleverer than myself could likely knock up a simple circuit so a single strike via a solenoid then reverses and resets - wouldn't even need a button push if using a break in a light path as the trigger - just a finger in a gap.

pgk

I thought of rossbows and airgun mechanisms as well, but beside the clapper issue you mentioned i'm under the impression that it would be a bit hard to load the spring. Maybe i'm wrong though.

Could you please explain the solenoid option? I'm afraid i don't understand what you mean

Thank you !

An Mich Kotzelbaum26/02/2022 08:32:06
9 forum posts
Posted by old mart on 25/02/2022 20:48:26:

How about the mechanism design similar to the bass drum pedal in a drum kit.

I thought about it, piano mechanics as well. Would definitely work, but most of users (children!) would push the "pedal" so that the hammer would dampen the tuning fork...

An Mich Kotzelbaum26/02/2022 08:36:32
9 forum posts
Posted by Martin Connelly on 26/02/2022 08:08:33:

Two tone door bells do this.

Martin C

Right! Thank you.. Too bad i can't use electricity

Maybe i can implement the plunger mechanism into the design though.. wink

pgk pgk26/02/2022 08:51:43
2563 forum posts
293 photos
Posted by An Mich Kotzelbaum on 26/02/2022 08:28:11:

I thought of rossbows and airgun mechanisms as well, but beside the clapper issue you mentioned i'm under the impression that it would be a bit hard to load the spring. Maybe i'm wrong though.

Could you please explain the solenoid option? I'm afraid i don't understand what you mean

Thank you !

You don't need a very strong spring or this purpose and any re-loading can be done with mechanical advantage - long lever or winding drum.
A solenoid is essentially a coil with an iron bar down the middle - apply a votlage and the bar moves one way, reverse the polarity and it returns. So you would need to assemble suitable parts (outside my knowledge to choose them) so that a switch triggers the action, gives the strike, that closes another circuit that returns the striker. It’s how early doorbells worked, switching back and forth to give a continuous 'burrrr..ing'. To have a single strike would mean designing things to reset the circuit after the one hit. Since we now know this is or children to use then simply need to have stuff running on simple batteries.

pgk

An Mich Kotzelbaum26/02/2022 10:02:24
9 forum posts

I got your point. I must experiment a little with loaded spring mechanisms to get a feeling, i guess.

I also like the idea of the finger in the gap, it would require a battery of course.. I don't feel confident enough with electromagnetism but it may be the simplest option.

Thanks again

An Mich

Circlip26/02/2022 11:08:34
1510 forum posts

Never seen the hammer chime on a Mantle clock???????

Regards Ian.

An Mich Kotzelbaum26/02/2022 11:29:41
9 forum posts
Posted by Circlip on 26/02/2022 11:08:34:

Never seen the hammer chime on a Mantle clock???????

Regards Ian.

No, actually

But it is definitely the concept i'm trying to break down and simplify for my purpose

thanks!

pgk pgk26/02/2022 11:35:18
2563 forum posts
293 photos

One of the simplest mechanisms that comes to mind would be an upward angled tube with an end cap with hole... rod with knob goes through there and compression spring with washer inside the tube. A loose ball bearing is shot along the tube when you pull back on the knob and let go, That hits tuning fork (or hits something that hits tuning fork) but cannot escape the tube end gap and returns by gravity.

pgk

Martin Kyte26/02/2022 13:24:21
avatar
2753 forum posts
48 photos

A simple hammer on a semi flexible rod mounted vertically from a horizontal rod pivoted t both ends. The horizontal rod carries a counterbalance on 2 right angled levers to bias the hammer against a stop just shy of the tuning fork. A short tail on the pivioted rod to act as the activating lever/key. The action is such that pressing the activating lever lifts the hammer away from the stop and on release allows it to fall back. The flexibility of the hammer rod allows a small over run such that the hammer hits the tuning fork. Adjustment is by counter weight choice and adjustment of the stop.

regards Martin

SillyOldDuffer26/02/2022 14:11:01
Moderator
8692 forum posts
1967 photos

Something like this maybe:

dinger.jpg

When the cam is turned it pushes the spring arm away from the tuning fork until the apex of the cam is passed. Then the arm springs back and dings the clapper into the tuning fork. Simplest arrangement is with a straight spring arm but a rigid arm could be hinged and powered with a coil spring, opposing super-magnets, or an elastic band.

Devil as always is in the detail:

  • Cam has to be positioned to bend the spring enough to deliver a suitably hard whack
  • Clapper has to be positioned so it only hits the fork once and doesn't bounce repeatedly
  • Cam shape determines the exact trigger characteristic (but I don't think it's critical)
  • Cam might be better positioned in line with the arm, or near the bottom, so it can be turned either way.

Meccano is quite good for testing experimental set-ups.

Dave

Jeff Dayman26/02/2022 14:34:17
2225 forum posts
47 photos

I'd suggest the same idea/mechanism as used in a Sten gun, adapted to "fire" vertically. Basically it is a fairly heavy steel rod running vertically inside a loose fit tube. There is a spring below the rod causing it to jump up and hit the fork when triggered. After impact the rod falls back down by gravity, and if the spring is adjusted just so, it resets the rod behind the trigger catch / sear, and re-compresses the spring for the next actuation. Again, weight of rod and strength of spring have to be adjusted just so to get the rod mass vs the spring force to work as described. A nut soldered or welded on the bottom end of the vertical tube, with an adjuster screw installed inside, would provide a simple length/force adjustment for the spring, to " dial it in ". The trigger could be made with a button on a release lever, or left as a plain lever. It also needs to have a light spring and a stop to allow automatic resetting with minimal force. Just food for thought.

As with all simple mechanisms gravity is your friend.

An Mich Kotzelbaum27/02/2022 07:44:05
9 forum posts

Wow, so many inputs. Thank you all!

I like all your ideas, i already started to make some prototypes, thanks God it's sunday

Jeff Dayman28/02/2022 14:33:59
2225 forum posts
47 photos

Be sure to post some photos of your progress An Mich, would love to see how this works out. Cheers!

An Mich Kotzelbaum28/02/2022 19:08:02
9 forum posts

I surely will! I started to assemble something like SillyOldDuffer suggested, but i must find a thicker spring arm. Yes, it's all a matter of experimenting different things by now, i never dealt with springs in a qualitative way, it's a good project to get a feeling about it!

Thanks again to all of you!

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