
This Student Invented a Stepper Motor Organ - mfburnett
https://www.youtube.com/watch?v=--sH0071ZDc#
======
jsheldon
I made this!

I tried posting this myself in Show HN, but I think I was getting caught in
the spam filter because I'm a new account.

Here is how it works, copied from the video description:

This is an experimental instrument I built that uses back-driven stepper
motors to synthesize sound. The operational principle is that when stepper
motors are back-driven, they induce a pseudo-sinusoidal alternating current.
If this signal is amplified and connected to a speaker, you can listen to it
as sound. The pitch of the sound is determined by the frequency of the wave,
which depends on how fast the motor is back-driven. Higher speed will be a
higher note. I thought this sound was interesting, so I wanted to make an
instrument that used this mechanism to make music.

There are 49 stepper motors, one for each note in my four octave instrument.
At rest, each motor floats above one of 49 disks, which increase in size
exponentially as the notes ascend in pitch. The disks spin together, driven by
a single speed-controlled DC motor. When a key is pressed, the corresponding
stepper motor is engaged with the corresponding disk in the disk stack, and
the disk back-drives the stepper motor. The larger disks are moving faster on
their outside edge than the smaller disks, so the stepper motors are driven
faster by the larger disks than the smaller disks. The disks are sized such
that all the notes will be in tune relative to each other. The key that the
instrument plays in is determined by how fast the disk stack is spinning. A
faster disk stack will play a higher key, a slower disk stack will play a
lower key. The speed of the disk stack is a global pitch shift.

Each note has a volume knob because the higher notes come in much louder than
the lower notes, so they need to be trimmed down.

The disk stack isn't built perfectly; it actually wobbles a little bit off
axis. Because the pitch of any note isn't actually determined by the radius of
the disks, but rather the instantaneous radius at the current point of
contact, this causes most notes to slightly fluctuate in pitch as the disk
stack rotates. This adds an interesting character to the sound.

Another interesting effect is that especially when spinning at higher speeds,
it may be difficult to get the higher notes to fully engage with their disks.
You have to push the higher keys pretty hard to get full engagement, otherwise
the note may go up to a half or full step flat.

------
mfburnett
This University of Maryland student made this experimental organ using 49
back-driven stepper motors this summer - absolutely incredible

------
defaultio
I made this!

I tried posting this myself in Show HN, but I think I was getting caught in
the spam filter because I'm a new account.

Here is how it works, copied from the video description:

This is an experimental instrument I built that uses back-driven stepper
motors to synthesize sound.

The operational principle is that when stepper motors are back-driven, they
induce a pseudo-sinusoidal alternating current. If this signal is amplified
and connected to a speaker, you can listen to it as sound. The pitch of the
sound is determined by the frequency of the wave, which depends on how fast
the motor is back-driven. Higher speed will be a higher note. I thought this
sound was interesting, so I wanted to make an instrument that used this
mechanism to make music.

There are 49 stepper motors, one for each note in my four octave instrument.
At rest, each motor floats above one of 49 disks, which increase in size
exponentially as the notes ascend in pitch. The disks spin together, driven by
a single speed-controlled DC motor. When a key is pressed, the corresponding
stepper motor is engaged with the corresponding disk in the disk stack, and
the disk back-drives the stepper motor. The larger disks are moving faster on
their outside edge than the smaller disks, so the stepper motors are driven
faster by the larger disks than the smaller disks. The disks are sized such
that all the notes will be in tune relative to each other. The key that the
instrument plays in is determined by how fast the disk stack is spinning. A
faster disk stack will play a higher key, a slower disk stack will play a
lower key. The speed of the disk stack is a global pitch shift.

Each note has a volume knob because the higher notes come in much louder than
the lower notes, so they need to be trimmed down.

The disk stack isn't built perfectly; it actually wobbles a little bit off
axis. Because the pitch of any note isn't actually determined by the radius of
the disks, but rather the instantaneous radius at the current point of
contact, this causes most notes to slightly fluctuate in pitch as the disk
stack rotates. This adds an interesting character to the sound.

Another interesting effect is that especially when spinning at higher speeds,
it may be difficult to get the higher notes to fully engage with their disks.
You have to push the higher keys pretty hard to get full engagement, otherwise
the note may go up to a half or full step flat.

