Strong but Silent Fan or Drill Motor

[mikeoliviero]

Hi Eng-Tip Forum,

I'm a musician looking to make an instrument for my music that uses a motor to spin a noise tube of sorts (like a ridged vaccum hose) to make a droning musical tone. I have the tubes, and I have made some rough prototypes of the idea where I attached a tube to an electric drill or electric fan motor to get the requisite spin. But I need a motor that is: (a) CHEAP-ish, ideally less than $100 (so that I can make 12 separate machines, one for each note of the musical scale, each with its own motor) (b) QUIET(so that I can put a microphone near it to amplify the sound, and (c) POWERFUL (each noise tube can access five notes, the higher the speed of the motor, the higher the tone that comes out of the tube, and it can take a lot of torque to get the high tones). If anyone has any suggestions for drill or fan motors that are cheap, silent, and super strong, I would be much obliged.

If you are willing to help with some guidance, I ask that you please be patient and kind with me. I know nothing of electronics (but I'm starting and willing to try to learn) and I am trying to get my bearings on how to approach this idea. I know from music-related forums that forum responders can sometimes speak harshly to unknowledgeable newbies like myself. Any help or insight you might be willing to offer would be greatly appreciated.

Thanks so much.
Mike

 

[racookpe1978]

The motor may need to go inside a sound-resistant enclosure, (even a thin wood box wrapped with loose insulation would tremendously cut down on noise outside the box).

How long would the motors need to run? (That affect a motor's DC battery ? or AC + speed regulator/"drill motor" squeeze-type speed regulator trigger.)
How many need to run at once?
How long are the tubes? How big a diameter are they? How fast are they turning. (Basically = How much power is needed to turn the tubes?) Have you tested your prototype motor and tube so you actually know how much power is required?

Musicians are a funny group - very, very picky about some things (think Stradivarious violins) where price is literally no complaint at all - at least buy those who want to sell a Strat; but utterly uncaring about other things. How closely do you need to close these tubes?

 

[mikeoliviero]

Hi recookpe1978. Thanks so much for your response. Your sound-resistant enclosure is a great idea!

The motors would only need to run for upwards of 6-7 minutes at any given time (the length of a long song), but usually only for a minute or two at a time during a particular section of a song. I was thinking I could attach some sort of a wall-plug to them, so batteries would not be needed (unless in mentioning a motor's DC battery, you mean that it is the case that they also have to have an internal battery in addition to an electrical supply?).

The tubes are anywhere from 2 to 3 feet long depending on the musical key or notes I am trying to get (shorter the tube, higher the key or note). They are about 1.5 inches in diameter and are a super lightweight plastic...slightly translucent...they are a children's toy actually (

http://www.stevespanglerscience.com/sound-hose.html).

I don't know how fast they are turning. I would need to try to suss that out and get back to you. I also do not know how much power is required. Pardon the question, but do you have any suggestions for how I figure out how much power is required?

Can I ask for clarity on your question of "how closely do you need to close these tubes"? Did you mean how closely do I need to a place a microphone? If that is the question, ideally, I was thinking some kind of a little lavalier mic close to the base that remains relatively stationary, while the other end spins in a wide arc. Or a big large diaphragm mic could be placed just beyond the reach of the wide spinning arc tube.

Thanks again for your help!
Mike

 

[dArsonval]

Your idea reminded me of a device I saw at an art exhibition. (Photo attached)
It was a hand powered rotating mirror sandwiched between protective glass panes.
The visual effect was a crowd-pleaser. Note the gearing used to produce the higher RPM.
A quiet “rope belt” and pulleys could be considered.

Protective mesh screens would likely be used in your particular application to allow full
capturing of sound. If a shaded pole motor was sized large enough using a similar arrangement
you could use dimmer switches as what’s found in controlling paddle ceiling fans for example to very speed.

Anything with a gearbox (such as a brushed universal drill motor) would contribute to additional noise.

A shaded pole motor like this,

http://www.grainger.com/product/DAYTON-HVAC-Motor-10J151?s_pp=false

doesn’t have a lot of torque however so compromises would have to be made somewhere in your design.
It –might--- have enough to fling a tube in circles though.

Others may chime in on a better approach, so allow some time to lapse here to see what further ideas come in.

Enjoying the Forum,

John

 

[tygerdawg]

Could you clarify:
(1) tube is gripped on one END, correct? (Not in middle?)
(2) tube is rotated in VERTICAL PLANE (parallel to wall) or HORIZONTAL PLANE (parallel to floor)?
(3) What RPM speeds are required?

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[Sparweb]

My son played with one of those tubes for YEARS.

Anyway I don't think the tube needs to spin to make noise. The airflow alone can cause the echoing eddies in the corrugations, no matter what drives it.

If it is just flow, not spinning, have you ever tried attaching a big bag and playing the tube like a bagpipe? Given the size of the tube it wouldn't take long to blow all the air out of the bag, but hopefully just long enough to prove that airflow, not spinning, is needed. If a good note can be produced for X seconds from a bag full of Y cubic feet of air, then the air flow rate can be worked out.
Armed with a known air flow, you can then go and pick a suitable fan.
Computer fans are pretty quiet, but I don't know if they're big enough. Though the specialty fans (for PC gamers) can be 24" across.

If you really do need to swing the tube, then the power required of the motor goes way up. And you'll need a variable speed so DC is the simplest to use, without busting your limited budget. Cars are full of motors to power-assist all kinds of things. Maybe a power-window motor would turn fast enough and be powerful enough for you.
If you had a bigger budget, then a medium-sized stepper motor might do it, and you could control the speed precisely. Takes a bit of book-learning to hook up a stepper and get it working though.


STF

 

[racookpe1978]

Hmmmn.

If you going to "play" tubes but at irregular times during a song, then you'll either need to be mobile and agile (like my daughter constantly running through the high school band "pit" hitting various percussion instruments at various times for various songs). Or, be able to run each motor to a switch box where you can start/stop/adjust (?) each motor separately.

To your question: Can I ask for clarity on your question of "how closely do you need to close these tubes"?

I should rather have said: "How close do you need to regulate the tube's speed?
"Almpst close enough" might give you the tone you need, or it might be totally "wrong". I have NO "ear" for tones, music in general, nor singing; and so cannot tell even if a tuba or trombone is playing correctly - though, if I am lucky, I can generally tell if one is playing at all. (Hint: If a trombone is playing, the slidy thingie is usually going back and forth. And the tube is playing if the player is getting red in the face. Redder face = louder tuba.)

 

[MikeHalloran]

I'm thinking 12 small 3-phase motors,
each driven by a small VFD,
all controlled by a PLC,
or maybe a Mac or PC with the right interface board,
plus a 4 wheel garden trailer to carry the 'instrument' from the loading dock into the venue,
plus a HF trailer to carry the garden trailer.
You drive the the VFDs from a fat extension cord,
or if the venue lacks convenient power,
include a big inverter
and a rack of batteries,
or just tie the batteries to the VFD's DC buses
and omit the inverter.
... all for $1200 total? That number is a bit optimistic.

Also, the notes may have some odd 'attack' and 'decay' signatures as the motors accelerate and decelerate. To minimize that, you may need bigger motors, etc., so you have to prototype one tube to get that sorted out.


A steam calliope might be easier to build.



Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

It may be interesting to control the air flow through the tubes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

If your idea is to have this as a droning type background sound,like a bagpipe, with some slowly variable pitches, this could be cool. Some friends and I did a sort of "Blue Man Group" (sans makeup) skit at a gathering where we made instruments from available materials. Mine was what I called a tube-a-phone (I played Tuba in high school) which was a garden hose that I twirled over my head and by changing the speed, I could get three different "notes" (they are all polyphonic tones actually), I'm sure with enough motor power you could get more. But it requires a significant change in speed to change the pitch, with little "half tone" variability in between, it's kind of a threshold change. So the ramp time between those thresholds is going to make it difficult to change tones rapidly unless you have a relatively powerful motor and stiff power source.

So on to the practical physics of it. To get to the motor power required, you will need to know the total inertia (mass) of the device, the peak speed you want to run it at and the rate of change in speed that you want to attain. This is why people were asking you for the way you intend on mounting and spinning the tubes, that will have the most effect on the power requirement, as those thin plastic tubes have almost no masss.

Once you have that, there are standard acceleration formulae that can be applied to get to a torque requirement, then when you know the torque and base motor speed, you can determine the power requirement. The tricky "Catch - 22" part is that the total mass must INCLUDE the motor rotor itself and any gearing/pulley transmission system to take a standard motor speed up or down to your peak level, but you will not know what that is until you have selected the motor. So the process is to run the calcs for everything else, determine a minimum power requirement, size a standard motor, then add the rotor/transmission mass back into it, then redo it and see if it still works with the motor power. If not, go to the next standard motor size and start over.

"Will work for (the memory of) salami"

 

[racookpe1978]

Would that work?

Blowing air through the tube?

or is that just what an organ does?

 

[waross]

I suspect that the airflow determines the volume, and the flow of air coupled with the velocity of the end of the tube determines the frequency. Not sure though.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MikeHalloran]

I remember those toys, and the haunting noise they make, very well. I think the noise comes from a cavity resonance that's excited by the airflow over the moving end of the tube. I don't think you can get the same sound by moving air through the tube.



Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

Hmmmn.
-Line of tubes, open end up.
-Row of blow pipes with solenoid valve aimed across top of tube.
-User plays solenoid switches with one hand, switches (keys - but not a keybard) trips open solenoid vale which ports air from compress cylinder (no noise!) from manifold into right valve across the top of the right diameter and length tube.

Might be easier than a helicopter array of whirling tubes in mid air starting and stopping and accelerating and slowing down all of the time....

Ain't quite a pipe organ, but it beats a bunch of red-faced tuba players.
But the tuba players would be cheaper.