Orbital Sound

A device that makes a noise without the use of batteries, that's small light and portable.

This device makes use of resonance in a cavity.

As its an acoustic device we need to provide it with air.

But rather than applying the air by blowing into it we will propel the device at high speed to force the air.

Supplies

3D Printer

BlocksCAD

Cura

Plastic Glue

String

Sanding Paper

File

Modelling knife

Handles (See Final assembly for further details)

Safety Glasses

2mm drill bit

Step 1: Theory

If both ends of a tube in a musical instrument are uncovered its an open end air column. E.g. woodwind instrument

The resonant frequency depends on the dimensions of the air column in conjunction with the air speed and temperature.

Anti-nodes or maximum vibration exist at the open ends of the air column with the length of the air-column half the wavelength of the fundamental frequency.

The frequency would be calculated as f =V/2L = 343.7 m/s /(2*0.012 m) = ~14.32kHz

However, being a sphere its a more complex process.

If we cover one hole the sphere approximates to a Helmholtz Resonator without a neck.

With calculated frequency of 72.6*SQRT(0.002/(0.012^3)) = ~2.47kHz

Both frequencies are within the audible range of 20Hz to 20kHz although there are variation between individuals particularly at the higher end.

However, the spinner is not travelling at a constant speed but accelerating and decelerating thus affecting the intensity and frequency of the sound.

Additionally, multiple harmonics are also produced at higher frequencies than the fundamental.

For the design spheres rather than cylinders are used as they offer better stability in motion offering less air resistance and being more streamline..

When the spinner is turning air passes quickly over the outer surface creating a pressure difference attempting to pull air out of the sphere conversely the lower pressure created attempts the suck the air back in.

These oscillations of the air repeat at long as the spinner rotates.

Step 2: Design

The device will be required to rotate rapidly without the use of batteries or electrical motors.

This will be accomplished with the energy stored in a wound string with an offset axis.

In order for the device to rotate smoothly it is required to be balanced and symmetrical, a circular object fits the bill.

The circular object will normally rotate in the vertical plane.

As this device was to be 3D printed consideration needs to be given to the overall shape, size, strength and aerodynamics.

The circular object comprises a supporting dual hoop wheel with 4 spokes and a central hole.

But this on its own is not what will make the sound we desire.

In order to make the noise we require some resonators.

The resonators will be hollow spheres with two holes, one at each of horizontally opposite aligned poles.

A total of four resonators will be included which will fit between the gap of the two spokes.

Two small oppositely placed rings will be placed close to the centre through which the string will be laced.

In order to negate the requirement for supports and ensure the spheres are hollow.

The device (spinner), will be created in two halves in order to print it flat and then the two halves will be stuck together.

Printing in two halves enables the spheres to be inspected internally for issues.

Design details:

Radius of the outer hoop is 32 mm

Radius of the inner hoop is 18 mm

Radius of the spheres is 7 mm with wall thickness 1 mm.

Radius of the holes in the spheres is 1 mm.

Spokes and hoop thickness is 2 mm.

Once the design is complete, its rendered in high resolution to create a smooth print then a STL file is generated.

Step 3: Print Preparation

Load Cura (used for this project) or similar splicing application.

Open the STL file.

As we require two halves to create the completed spinner we need to create a multiple of the object.

This is accomplished by right clicking the object and selecting "Multiplying selected object".

Enter 1 in the dialog box (as we only require one object), and select OK.

The additional object will be placed on the bed.

Right click on an object and select "Select All Objects".

This will allow all the objects to be moved as a group to enable centring on the bed.

Once the objects are positioned assign the printer settings.

In the case the settings are:

Layer Height - 0.15 mm

Infill - Tri-Hexagon

Infill Density - 50%

Base Adhesion - Brim

No supports.

Filament - PLA

Weight - 9 grams

Print Time - 1 hour 22 mins

Save the Gcode file for the printer.

Step 4: Printing

Print using PLA or other suitable filament in a colour of your choice.

You could even print the two halves in different colours.

Step 5: Post Processing

Once printed remove the Brim.

Remove any blemishes or strings from the surface by filing, sanding or cutting.

Sand the flat side of the spinners to remove any roughness as this will help ensure the surfaces fit together evenly and prevent gaps in the spheres that will affect the sound due to air leakage.

Regarding leaks, the 3D printing process is known to produce small gaps between and in layers as a result these will require filling in.

The gaps are filled in with lacquer, enamel paint or epoxy resin this is applied both internally and externally and left to dry.

If necessary clear out the holes in the spheres with a 2 mm drill bit.

Clear out or widen the holes for the strings as required.

Following this a suitable plastic glue is applied to the flat surfaces of the two halves and these are bonded together.

The spinner is complete.

Step 6: Final Assembly

Measure approximately 1 metre (39 inches), of string/twine.

Thread the cord through both string holes to form a loop and tie the ends together with a suitable knot, I used a square (reef) knot.

Handles.

Subject to the string diameter and finish you may wish to add handles or use gloves to prevent the string rubbing your fingers.

Handles may be created from the following:

Two large body felt tip pens (loop the cord around the body), dowels (looped with cord or through holes), or circular disc cut from wood (loop cord through hole and body). Other options may be considered such as 3d printed handles.

Step 7: Operation

Before use and periodically during use check that the spinner has no issues and that the string is not fraying.

If any issue are found better to reprint a new spinner and to re-thread with a new string.

As a precaution wear eye protection in case there is a failure of the spinner or the string should snap.

Without handles:

Stretch out the string loop to form two parallel lines with index and middle fingers of each hand looped through the turns at the extremes

Clasp the string in closed fingers.

With handles.

Stretch out the string loop to form two parallel lines clasp the handles in closed fingers.

The rest of the process is applicable to either method.

Centre the spinner along the string so as to be positioned equidistant between your hands by sliding along the string loop.

Hold the string loosely with forearms parallel such that the spinner and string form a "V" shape with the spinner at the bottom of the "V".

The string is tensioned by rotating both hands in unison (creating small arcs), maintaining the "V" shape (as far as possible); as the string tightens it should shorten as it is wound.

Once the string starts to produce kinks, it is would sufficiently.

At this stage maintaining parallel forearms pull your hands outward away from each other.

The spinner will start to spin unwinding the twist previously applied whilst simultaneously whistling.

Once unwound the momentum will cause the string to wind its self in the opposite direction but at the same time losing momentum and slowing down.

During this stage relax the opposing pull between your hand and pull them apart again causing the spinner to rotate in the opposite direction picking up speed in the process.

Repeating the process with a smooth co-ordinated action will keep the spinner rotating and whistling.

It may take a little practice the get the spinner to rotate.

It's also a good exercise for your arms.

Comments

[Art_Lieberman]

I, too, used to make these with a large button 60 years ago, taught by my dad. And I just now finished making Gammawave's project. I cleaned the holes on the spheres, but I did not clean the insides of the spheres where there was a lot of stringing. I applied Gloop only to the spheres for connecting the two halves - nothing else. Did no additional cleaning. And it works great, including the whistling!

[Gammawave]

Thanks for the comment. Perhaps erring on the side of caution. But trying to ensure that I minimised the risk of it not working. But glad you have no issues.

[Art_Lieberman]

It was intended to be a compliment, that your great design works, no matter what.

[Gammawave]

Taken as such, thanks; much apprecated.

[deedsdone]

as a small boy my mother would tie knots around a handkerchief and i could wear it for a hat! and for amusement she would put a button on a thread looped through the holes and i could spin the button very fast and the harder you pull on the string and the farther you let it unwind the faster it would go! and it would go so fast it would start to hum and buzz. faster as it unwound and slower as it wound up. The pitch of the sound would go higher then lower So fast the string would break from the torque created by that little button on a thread! i was mesmerized by your instructable as you broke down the entire process very concisely, scientifically, intelligently... i rather enjoyed reading it.and id like to tell you that i made this project........fifty some odd years before this was posted....so it probably doesnt count or qualify but i think my mother referred to it as a gypsy top or a gypsy yo yo!!
very well done ! Intriguing!! now i'll have to make one from a button and a thread!

[Gammawave]

Thanks for taking the time to comment. Seems there is nothing new under the sun and though technology and materials may change some things are just waiting to be rediscovered. Happy it brought back fond memories. Did a search on the names you referenced the first returned a yo yo magic trick which can be found on youtube (no connection but my original train of thought was triggered by a yo yo, but not previous seen this), the second returned an item of clothing. If you do make one, post it the site and the fifty odd years connection will be rejuvenated.

[jeanniel1]

We used to use large buttons (2 of them at least 1" in diameter), string them up so that they could whirl apart and then back together with a "Clack!" Hours of entertainment!

[Gammawave]

Thanks for that will have to give it a try. Perhaps time for a resurgence in such things that don't require batteries for a new audience so that they are not totally forgotten.

[jeanniel1]

I second that!

[ElizabethD97]

This is such a neat design. I had to try it. I printed both halves as directed, but I just can't seem to get it to make a sound. I can get it spinning no problem, but the sound doesn't have that cool whistle noise yours does in the video. It's just the wind sound. I cleaned out the holes to make sure they were clear, but nothing. Do you have any other suggestions?

[Gammawave]

Problems can ensue if the spheres are not fully sealed at the interface of the two halves when glued.
in addition any small gaps in the body creates leaks hence painting the inner and outer of the spheres with paint or lacquer.
This is the first area to check out.
The hole sizes when printed at the correct scale are less critical 2 - 4mm is within the working range.
However, you could make the holes slightly bigger within this range if its not working at 2mm.
I am assuming this is printed at the default size as larger or smaller spheres tend to display the issue you are having.
Is it well balanced when spinning as this can make it difficult to get a consistent spin and thereby affect the sound.
Let me know how you get and If you have any images feel free to send.

[ElizabethD97]

That is super helpful. I went through and sanded down the edges and sealed them. It's not as loud as the one on your video, but I'm getting a little sound! Thank you!

[Gammawave]

Glad to help :)

[jayprab56]

Back in the Old Country (India), we used to make this out of bottle caps and such. They didn't make sounds like yours does, but, pre-TV, we were endlessly entertained by such simple things... I made one each for my 6- and 8-year old nephews and they were, lets say, underwhelmed...

[Gammawave]

Thanks for taking time out to comment.
Different times, different technology, different expectations.
One basis function which perhaps does limit its entertainment potential.
So maybe a version incorporating electronics with the addition of lighting effects for an audio/visual experience may be more appealing?

[jayprab56]

Yes, I thought of making one that used lights and a kinetic energy source that harvest energy from the act of spinning the toy. That way, it wouldn't add to the used-battery-load in waste dumps. I had NOT thought about sound, just light. The edge of the toy would have the LEDs and they could spell out words and messages, synced to the spin RPM

[Gammawave]

Definitely, an idea waiting to see the light of day :)

[jessyratfink]

That is a wild sound!

[Gammawave]

Even wilder it only creates this sound when accelerating and decelerating under specific conditions and not at a constant velocity.
The hole in the centre was used for additional experimentation and accommodates an M3 nut and bolt which was then tightened and fitted in an electric variable speed drill. No whistling just the sound of the drill.
Just to determine if this was specific to this model I have made some variants with different spheres sizes and different hole sizes and placement, all are silent when spun with a drill.