An Organ Made From Back-Driven Steppers

[Josh] wrote in to tell us about an experimental instrument he’s been working on for a couple of months. We’re glad he did, because it’s a really cool project. It’s an organ that uses the principle of back-drive—applying torque to the output shaft of a motor—to create sounds.  [Josh] is back-driving four octaves worth of stepper motors with spinning wooden disks, and this generates alternating current. At the right speeds, the resulting sinusoidal waveform falls within the range of human hearing and can be amplified for maximum musical enjoyment.

[Josh] built this organ from the ground up, including the keys which are made from oak and walnut. Each of the forty-nine stepper motors has a corresponding wooden disk. The larger the wooden disk in the stack, the higher the resulting pitch. [Josh] says that if he built it for a full 88 keys, the highest note’s disk would be sixteen feet in diameter.

This stack of disks is driven independently by a separate DC motor, and the speed determines the key it will play in. When [Josh] plays a note, that note’s lever is actuated and its stepper motor makes contact with its disk in the stack. When they meet, the motor is back-driven by the spinning disk. In other words, they work in concert to produce some cool, eerie sounds.

Here’s a somewhat similar sort of build made from lasers and fans, if you consider that both instruments create music from objects that weren’t built to do so. Watch [Josh] play his stepper organ after the break. He has several build videos on his YT channel, and we’ve also embedded the one that covers the motor, power, and electronics part of the build.

Building the electronics:

17 thoughts on “An Organ Made From Back-Driven Steppers

  1. Shades of the Hammond B3! Very interesting project. Great job of thinking outside the box (by the way … what IS a box?).

    A second “deck” of steppers with drive wheels twice the circumference of the original ones, running on the same path would give you 1/2 the frequency of the original (one octave lower). You would, of course, need a larger keyboard and a slightly different linkage, but you are limited by the number of keys and steppers you are willing to assemble. Looks like there’d be room for several additional “decks” … so start building that foot pedal assembly.

    Electronically converting the output of a second bank of steppers falls outside this interesting design (divide the second “deck” stepper outputs by 2 for example); I mention it in case you don’t like making drive wheels.

    1. I was watching the video and thinking,” Wow, this is very reminiscent of Wintergatan.” Then I scrolled down to the comments section, and the top comment was from Wintergatan…

    1. Just guessing but it might be both. We hear, on the video, the sound from it’s jack plug output. I bet in real life it makes quite a racket. Hence headphones rather than speakers. Might be it’s only possible to play with either headphones or BIG speakers, at a distance from the audience.

  2. Sounds a little bit dischordant, and could do with being an octave higher. Of course, the design is genius. I suppose the drive wheel isn’t quite stable, speed goes up and down a bit, which will add a vibrato effect, for free!

    I wonder if you could build a smaller one using mobile phone vibrator motors? Doesn’t have to use steppers. Also wonder, if he used different combinations of the coils on the steppers, could he do other octaves? He’d need an enormous multi-way switch. Or lots of little ones, perhaps giving him selectable octaves for parts of the keyboard.

  3. Wintergatan was mentioned as a driving inspiration in the article, but the fun part is that everyone has an idea about doing it better or differently – seems to have fired up some imaginations.

    Two immediate thoughts apart from the previous comments:

    This reminds me a great deal of Benjamin Franklin’s glass armonica.

    Making a continuous tone wheel would be pretty interesting, allowing you to “bend” notes with a lateral drive on the traction wheels. Stepper motor blues, anyone?

  4. Is there a problem with tuning it right? It sounds like it gets detuned as more steppers touch the wheel shaft. Do you have the right circuitry to maintain the speed of the shaft regardless of the breaking force applied by the steppers touching it?

  5. Not the Hammond, but the Telharmonium with out the 3000volt high impedance output. I haven’t watched the vids yet cause the blues is so hot on the radio right now. I use stepper motors as “turntables” and get a badass bass woomp or subsonic coo. Flywheel adds sustain, switch shorting unused windings gives quicker decay. Some motors from old 40Meg hard drives for head positioning (not voice coil) have many more poles than printer motors do. One printer motor as a generator is able to generate some power, hooked directly to a speaker it will whine. Thus this instrument should be able with the diode mixing or resistance mixing be able to direct drive speakers like the Telharmonium did thru the phone network just over a century ago. Drive the tapered drum with a clockwork and use weight or springs and make it alternate power source. It will survive an EMP! A speaker suited for each range and for each “pipe” would be even greater effect, no mixing at all.
    Critique after watching video. An incandescent light dimmer on such good wood construction and all. Yuck. Never the right pitch. Either use an induction motor at full speed better synchronous, or use a DC PM motor on a regulated DC supply (tape drive motor from VCR) for a much more constant but variable drive. When demoing an instrument, it’s good to play the range of it as well as to try and perform a piece on it. The piece should be played up an octave, less bass more tone. These motors seem to be head positioning for floppy drives. They have the least number of poles per rev, so good for bass except they have a tinny tone vs. the smooth bass of a platter motor. Petal wheel printer motors have a large number of poles also.

    1. Use motors with 400 full steps and the drive wheels could be much smaller. And for cripe’s sake, use a drill press and/or jig to bore straight holes. :P Looks like it would eventually shake itself apart.

  6. I’ve been collecting components for something quite different from this for quite a while now. Hope I’ll be able to show it off this year. Such projects always take serious time. Good one.

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