Accordion Automation

This post shows some of the steps I went through to automate the treble section of the accordion.

I came across this website that describes the use of car windshield wiper motors to animate large Halloween projects:

http://www.scary-terry.com/wipmtr/wipmtr.htm

The windshield wiper motor provides more than enough torque to raise the bellows. In fact, I removed some of the pulleys I had previously installed on the device. With fewer pulleys, less rope has to travel to move the bellows. This makes them much more responsive to the motor movement.



When the bellows are at their greatest extension, the wiper motor must be reversed to allow gravity to squeeze out the air contained within. I used a couple of reed switches to sense when the bellows are fully extended and send a signal to the Arduino board that controls the accordion. One reed switch is attached to each side of the device for redundancy.


Small rare earth magnets were attached to the extension structure of the bellows. The reed switch contacts close whenever the magnets pass by, sending a signal to the Arduino controller.


Solenoids are used to pull the accordion pallets to select which notes are played. Bicycle brake cable is used to transfer the pulling motion of the solenoids to the accordion pallet arms. I experimented with a couple different strategies of connecting the brake cable to the pallet arms. I developed some laser-cut clips that wrap around the pallet arm and accept the ball-end of the brake cable. I designed break-away arms on the clips to aid with their installation in the tight spaces between pallet arms.


The clips worked with light tension on the brake cable, but they failed with a heavy tug. The acrylic did not have enough strength in the tiny dimensions that I had to use in the clips and did not fit inbetween some of the pallet arms. I designed another piece that uses the cable itself to wrap around the pallet arm, saving quite a bit of space.


I built a couple of oak brackets to fit over the front of the accordion to align the brake cables and hold the brake cable housing.


The placement of the brake cables translates the order of the accordion pallets to the order of the solenoids.



I adapted a computer power supply to power the windshield wiper motor and the relays that control them. I clipped and insulated the wires that weren't needed, leaving only two yellow 12V wires and two black ground wires exposed from the power supply. The green power wire was permanently connected to a ground wire to keep the power supply on.