# how to tune a vibrating motor - total novice

#### John Bosler

Joined Dec 12, 2014
2
I want to build a musical instrument based on tunable vibrating motors. I have bought a couple of these from amazon:

http://www.amazon.com/gp/product/B00CFSYQCS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

which I believe will change their RPM, and therefore frequency, by changing the voltage going to them.

Can someone recommend a very simple circuit, using a 9V battery or wall power supply, that would allow me to "tune" the frequency of this? I'm assuming involving a potentiometer and hopefully not a lot else!

Assuming I can get that to work, the idea is to have 8 or 12 of them running, all powered from the same power source, but each with a different voltage so I have a whole octave. But the first step is to make one or two tunable. Thanks for any advice!!

#### MrChips

Joined Oct 2, 2009
21,911
Assuming the maximum motor speed is 7000 rpm, that's about 117Hz.

You will be looking at two octaves below middle C which is very low.

The lowest note on my bass guitar is E, 82Hz.
The next string up is A, 110Hz.

If you want to create a bass instrument that is all you're going to get.

#### GopherT

Joined Nov 23, 2012
8,012
I want to build a musical instrument based on tunable vibrating motors. I have bought a couple of these from amazon:

http://www.amazon.com/gp/product/B00CFSYQCS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

which I believe will change their RPM, and therefore frequency, by changing the voltage going to them.

Can someone recommend a very simple circuit, using a 9V battery or wall power supply, that would allow me to "tune" the frequency of this? I'm assuming involving a potentiometer and hopefully not a lot else!

Assuming I can get that to work, the idea is to have 8 or 12 of them running, all powered from the same power source, but each with a different voltage so I have a whole octave. But the first step is to make one or two tunable. Thanks for any advice!!
There are two options for a musical instrument.
In both cases, mount the motors to a box with a hold in it (like an acoustic guitar body) to maximize the volume.
In both cases below, you need motors with very low inertia so it can change speed quickly.
Also, in both cases, you will only be able to change tone (frequency) with rpm. You will not be able to change volume (unless you add a mechanical system to cover/dampen the sound box.

One. Like you planned - the input signal varies the rpm to make the notes you want.

The other option (and the one I think you are after) is to connect the input signal to a high gain amplifier to essentially make a square wave with a bridge to allow forward and backward direction). This case, the motor will literally vibrate forward and backward to create audible sound - especially with the eccentric weight on the motor you posted. You will get only the bass - low bass notes as the motor cannot respond quickly enough to make higher notes. Also, the heavier your weight is, the more you attenuate (shrink) the higher frequencies. Without the weight, you will be able to hear the tones up to maybe 120 Hz. With the weight, maybe up to 60 to 80 Hz (just a guess).

Sounds like a fun experiment but don't get your hopes tok high on high fidelity performance.

PS, I tried the vibrate method when I was about 10 years old. I simply connected a small motor to a headphone jack of a stereo receiver. I could hear the sound as the motor vibrated in my hand.

I guess a very easy way to try this is to connect to the speaker wire of an old stereo receiver. Add a 5 to 8 ohm resistor in series to insure you have at least 8 ohm load for your receiver. Do this with the crappy old receiver, not with anything valuable. Make sure you don't touch the speaker wires together with out resistance.

#### Bernard

Joined Aug 7, 2008
5,657
For experimentation ( simple inefficient ) might use power darlington as emitter follower & 5k pot for each motor. D1326, isolated, 8 A, 60 V, gain 2000, or something similar. Drain might be around 100 mA per motor. Better one comparator, FET, pot per motor.

#### John Bosler

Joined Dec 12, 2014
2
There are two options for a musical instrument.
In both cases, mount the motors to a box with a hold in it (like an acoustic guitar body) to maximize the volume.
In both cases below, you need motors with very low inertia so it can change speed quickly.
Also, in both cases, you will only be able to change tone (frequency) with rpm. You will not be able to change volume (unless you add a mechanical system to cover/dampen the sound box.

One. Like you planned - the input signal varies the rpm to make the notes you want.

The other option (and the one I think you are after) is to connect the input signal to a high gain amplifier to essentially make a square wave with a bridge to allow forward and backward direction). This case, the motor will literally vibrate forward and backward to create audible sound - especially with the eccentric weight on the motor you posted. You will get only the bass - low bass notes as the motor cannot respond quickly enough to make higher notes. Also, the heavier your weight is, the more you attenuate (shrink) the higher frequencies. Without the weight, you will be able to hear the tones up to maybe 120 Hz. With the weight, maybe up to 60 to 80 Hz (just a guess).

Sounds like a fun experiment but don't get your hopes tok high on high fidelity performance.

PS, I tried the vibrate method when I was about 10 years old. I simply connected a small motor to a headphone jack of a stereo receiver. I could hear the sound as the motor vibrated in my hand.

I guess a very easy way to try this is to connect to the speaker wire of an old stereo receiver. Add a 5 to 8 ohm resistor in series to insure you have at least 8 ohm load for your receiver. Do this with the crappy old receiver, not with anything valuable. Make sure you don't touch the speaker wires together with out resistance.
Thanks!! That is super helpful. I am definitely not after high fidelity. My goal is to be able to touch the motors to different instruments, for instance acoustic guitar or something else that will resonate. I am hoping for a higher frequency than 120hz though, more like 250hz - 500hz. I actually got the idea from touching my sonicare toothbrush to a dobro guitar. I think the sonicare is about 500Hz. If anyone has an idea how to create that let me know!! And if anyone has a kid who is into electrical engineering and wants to try to create this I might be willing to pay a little bit +plus materials..

#### MrChips

Joined Oct 2, 2009
21,911
When you touch your electric toothbrush to a sounding board you will hear higher frequency harmonics and not just the fundamental frequency.

#### GopherT

Joined Nov 23, 2012
8,012
Thanks!! That is super helpful. I am definitely not after high fidelity. My goal is to be able to touch the motors to different instruments, for instance acoustic guitar or something else that will resonate. I am hoping for a higher frequency than 120hz though, more like 250hz - 500hz. I actually got the idea from touching my sonicare toothbrush to a dobro guitar. I think the sonicare is about 500Hz. If anyone has an idea how to create that let me know!! And if anyone has a kid who is into electrical engineering and wants to try to create this I might be willing to pay a little bit +plus materials..
The sonicare has a rather special actuator motor that is more like a hair clippers. It doesn't exactly rotate ( depending on the generation you have).

If you are looking for super speeds, there are smaller motors than you found. You can solder/crimp a fishing weight on it to cause vibration. The little cell phone vibrator motors could reach 12000 rpm (200Hz).

Start with something - you may/may not be satisfied. Then refine if needed.

#### ronv

Joined Nov 12, 2008
3,770
Almost everyone has an old disk drive around. The actuator is a high torque low inertia motor probably capable of small movements at 500 Hz. or more. The mechanic might be tricky.