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music box
aeropic Posted: 30 Apr 2022, 04:04 PM
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Hi, first of all huge congratulations for your ideas and your humour too !
I do love the music box and I must say I'm very tempted to build one, just for the fun of it !

Listening to your video I understand you did not go the way of a push-pull mechanism to rotate the washers.
The reason you invoque is the added latency... Do you think that it would be huge to move the servo arm a little bit backwards to rotate the washer by a few degrees more ? If I understand well the extra motion would be twice the few degrees (once in each direction) ?

I'm just afraid of wearing the plastic parts...

Anyway, this is such a cool project :-)

Regards
Alain

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mit Posted: 30 Apr 2022, 05:04 PM
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yeah whatever

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Hello. I'm afraid I don't fully understand your question.

The motion of the fingers is just push then pull. Forwards then backwards. It was originally going to be backwards then forwards, which would add latency, but hold the wafers away from the tines.

Since making the video I came up with a better solution to keeping the tines free until needed, I added a thin plastic comb on the opposite side (laser cut acetate on some laser-cut acrylic).

(User posted image)


(User posted image)


This is pretty effective at stopping the buzz noise when the wafers hit the tine on their way round. When the finger pushes forwards, the acetate comb is just pushed out of the way.

I wouldn't worry about wear on the plastic parts, I've had dozens of hours of use out of the music box with basically no maintenance.

A few people have built copies of the music box, one person did it with entirely 3D printed parts, I was very impressed (it involved a lot of sanding to get the bits to move smoothly).

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aeropic Posted: 1 May 2022, 09:05 AM
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whooaoo thanks for your answer and your new idea...

My intention was to 3D print long U shaped fingers

On the left the servo.
The first corner would push the washer while the bottom one tip would finish rotating the washer after the note when the finger is pulled back by the servo.

The final idea was to get rid of the motor to suppress the noise from it.
With your comb, I do not understand if the motor is still needed ?
To play a note, if I understand well, the washer must be rotated by 90°. But the push finger cannot perform a full 90° rotation as the washer will enter in contact on the finger's left part ? Can it ? I understand that it was the job of the motor to finish the rotation when the finger is pulled back to clear the washer. Am I wrong ?

I have to understand better the geometry of the thing ...
I ordered my music box waiting for it from China. I got it very cheap for 25€

(User posted image)


Last edit by aeropic at 1 May 2022, 10:05 AM

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mit Posted: 6 May 2022, 09:05 AM
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yeah whatever

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Yes, the motor is still needed in my design. I moved it and added a belt drive to reduce noise.

I would be interested to see if your method works. I've spent a while trying to think of a good design for it but never came up with anything better.

Also worth looking at the design of harpsichord plectrums - they have a one-way mechanism to pluck the string similar to what's needed for the musicbox. https://en.wikipedia.org/wiki/Harpsichord#Mechanism

I had an idea to make laser-cut plectrums from delrin, but never got around to trying it.

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aeropic Posted: 6 May 2022, 11:05 AM
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Meanwhile i started drawing something more detailled even if I don't yet get the music box nor its measurements!
I have the feeling it should work...

Here are some screenshots. The first one shows the position of the finger just at the end of the push motion (after the note) the washer is rotated to its green position.
Then the servo pulls the finger to the left and it comes in contact with the washer at the bottom right. it will then push the washer from green to blue position and the top left pin is ready to be hocked for next move...

only concern is to know if there would be room enough between the shaft+washers and the aluminum body. maybe some filing will be needed ?

I will have a look to the harpsishcord thanks...


(User posted image)


(User posted image)



As I don't want to spend hours sanding the 3D printed parts, I wonder if I could print them 0.1mm thinner while keeping them aligned and spaced with a piano wire going through the full length of the finger and sliding into a drilled piece at the right ... (I'll make a drawing !)

I made huge progress on the software, I intend to use an ESP32 to get MIDI over BLE. Meanwhile the USB version is able to receive note-ON commands in real time from the PC (arduino IDE is not as nice as assembly language but the embedded library makes the sofware so easy with only 3 lines of code to get the notes).
I will simplify wiring using PCA9685 I2C 16 PWM drivers...


Last edit by aeropic at 6 May 2022, 11:05 AM

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aeropic Posted: 14 May 2022, 05:05 PM
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I received my music box.
Indeed punching the holes in the cardboard is a pain.

I coded a small script which eats a midi file as input and generates and openscad file.

Then 3D printer to make the physical board. Of course the huge limitation is the length... Anyway it starts playing music :-)

(User posted image)


Last edit by aeropic at 14 May 2022, 05:05 PM

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mit Posted: 15 May 2022, 10:05 AM
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yeah whatever

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Oh, very interesting! That's a really neat idea.

Something I would like to try is using a vinyl cutter to make the strips. It would have to be fairly thin card stock, thin enough for the blade to cut through, but still strong enough to play the music box. The benefit of the vinyl cutter is you can just get a roll of material, and cut something as long as you like.

Another option I considered is to make a holder for a roll of thick paper to go in the laser cutter. You can just unplug one of the stepper motors and connect another one to create a rotary axis, I've done this in the past to etch onto round objects.

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aeropic Posted: 15 May 2022, 06:05 PM
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definitely the roll idea is a good one !
Anyway the best option is to get it automated ;-)

I just tried to print a piece to guide 1.2mm inox rods (the one used for RC plane servo rods). It seems it directly pushes with 100% success the washers. (imagine it upside down with the rods being guided by the vertical walls and sliding directly on top the metal table of the music box)
With this there would be quite no effort to make the auto music box as there would be no fingers.
But, of course, the motor to rotate the axis would then be needed...

(User posted image)


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