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MIDI Music Box pushrods
hsamuels Posted: 25 Dec 2023, 03:35 AM
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Joined: 25-December 23
As a radio-controlled airplane hobbyist, I can't help but notice the similarities in function between the brass wires on the music box and pushrods for control surfaces on the planes. On airplanes, you really don't want the pushrod to bend when it is pushing. One method of making lightweight rods that can both push and pull with minimal deformation is to cut most of the rod from a length of carbon fiber.

Add a short piece of Z-bend pushrod (steel wire with two 90-degree bends to fit in a servo arm hole) to the end of a carbon fiber rod. These are available at hobby sites and on Amazon, Aliexpress, etc. You can bend them yourself with a pair of needle nose pliers, but it's hard to make crisp 90-degree bends. A specialized tool called Z-bend pliers does this nicely.

Attach the wire to the carbon fiber rod by:

1. Lightly sand an overlap length of the end of the CF rod.
2. Align the steel pushrod with the sanded end of the CF rod.
3. Wrap the overlap area with thread. You may use a bit of tape to hold things in place for this step. Alternatively use heat shrink tubing, and shrink it over both rods.
4. Saturate the thread with thin cyanoacrylate, or drip the CA into the inside of the heat shrink tubing.

Wire attached to CF rod using heat shrink method

(User posted image)


Z-bend wire on servo arm

(User posted image)


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hsamuels Posted: 25 Dec 2023, 03:36 AM
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Here's the Z-bend in the servo arm.

(User posted image)


Last edit by hsamuels at 25 Dec 2023, 03:37 AM

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mit Posted: 26 Dec 2023, 10:59 PM
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yeah whatever

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Joined: 4-May 16
Interesting. Yes, I probably should have looked at existing pushrods for RC planes given that I was already using RC hobby servos. One method I thought about after building all those brass rods was laser-cutting the whole thing, not from acrylic because it's too brittle, but maybe steel if I sent off for it. Each rod would be cut to the exact shape including the z-bend, cutting in the plane that would allow that to happen. Delrin might also work, you could make them tall to add some stiffness.

Over the years since building that thing I have put a LOT of thought into other ways of making it. There's one totally different method that I really think would work, I made a start on it, but never finished. Hopefully one day.

The cotton thread/CA glue trick is one I use often. I started doing it (thought I had invented it) after reading a book about Pykrete.

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