Magnetic Spinner

Magnets have many practical uses in everday life but they can also be used to have a bit of fun with play and learning.

A quick project (under an hour), with the listed materials that should prove interesting with young and old alike demonstrating, magnetic attraction, repulsion and gyroscopic effect all embodied in a small toy spinning top.

Although, the design incorporates 3D printed elements for a repeatable consistent build, incorporating robustness permanence and colour co-ordination.

The project can still be realised without access to a 3D printer and alternative build options with few materials are described within.

Dimensions: 38(H) x 34.8(dia) mm

Weight: 42g

Main Supplies

Filament PLA+ Green

Disc Magnets with hole (Size: 31(dia) x 4.75 (thick) with 9.5 (dia) hole [mm]) - Qty 4

Carbon Steel Ball Bearing 10mm(dia) [larger than the diameter of the hole in the disc magnet]

Plastic Sheet ~5mm thick

Plastic Tray or Plate

Adhesive Putty (tacky)

Alternative build supplies

Glue

Clear Tape

Heat Shrink Tubing 35mm (dia)

Epoxy Putty

May prove more cost effective to buy a range of values rather than individual values unless you already have them available. Some components may also have a MOL greater than the quantity specified in the component list

Tools

3D Printer

Sanding paper

Craft knife

Know your tools and follow the recommended operational procedures and be sure to wear the appropriate PPE.

When using magnets be sure to follow the manfacturers operational and safety recommendations. (Example below).

Magnets Health and Safety document

Where minors are involved the project is to be constructed under adult supervision due to the use of magnets and small loose ball bearing.

The adult involved is fully responsible for ensuring that the activities associated with the project are carried out safely.

No affiliation to any of the suppliers used in this project, feel free to use your preferred suppliers and substitute the elements were appropriate to your own preference or subject to supply.

Links valid at the time of publication.

Some properties of permanent magnets in relation to each other are:

Two poles named North (N) and South (S) based in relation to the Earths magnetic field and the direction the end of a magnet points.

1: Opposite poles attract; N attracts S and S attracts N.

2: Like poles repel; N repels N and S repels S.

We make use of the magnetic attraction to bind multiple magnets together to create the major mass of the spinner whilst increasing the combined magnetic field to provide a balanced magnetic attraction with the multiple magnets on the back of the base to enable the spinner to be inverted without falling off.

Some properties of ferrous metals are:

They contain magnetic domains which in the unmagnetised state are randomly arranged but when subjected to a magnetic field and sufficient domains align to the applied magnetic field which may be N or S the metal is attracted by the opposite pole of the magnet.

This property is used to create a concentrated field at the point of contact on which the spinner is balanced and a weaker field around the edge of the disc magnet between the magnets in the spinner and the magnets on the back of the base and hold the spinner in place.

With no magnets on the back of the base the spinner can and will wander as there is no binding force.

Gyroscopic effect:

This refers to the way a rotating object wants to maintain the axis of its rotation.

Rotating the spinner imparts torgue and angular velocity and angular momentum keeps it spinning which depends on its mass and velocity. A heavier object has more momentum than a lighter object and a faster moving object has more momentum. Therefore, greater mass and speed equates to greater momemtum increasing the Gyrospcopic effect. If momemtum is maintained the spinning top keeps rotating but the system is lossy due to friction at the point of contact, gravity, wind resistance and in this case the inclusion of magnetic drag which ultimately causes the top to fall over and stop spinning.

Minimising these effects will prolong the spin.

The project was designed using BlocksCAD and consists of the following elements:

The dimensions of the Spindle and Protective Body to be 3D printed are:

Spindle: 11.8 (L) x 11.8 (W) x 28 (H) mm

Protective Body: 34.8 (L) x 34.8 (W) x 10 (H) mm

The Spindle simply pushes into the centre of a pair of stacked disc magnets and enables the used to rotate the spinner.

The Spindle and magnet combination fit into the Protective Body which supports and protects the magnets from damage due to impacts.

A ball bearing is inserted up through the centre hole in the Protective Body and held in place by the magnetic field.

The spinner rotates on the ball bearing.

Although, I have 3D printed the main supporting elements which gives it a degree of permanence, this is not absolutely necessary to make the project.

These can simply be substituted with tape wrapped around the magnets to replace the Protective Body and a dowel suitably shaped to replace the Spindle.

However, feel free to experiment with different materials.

The elements are printed with the following settings:

Filament: PLA+ (I chose to use a green filament but any colour would be equally applicable.)

Layer Height: 0.15 mm

Infill Density: 100%

Base Adhesion: Skirt

Spindle: Print Time ~15min, Weight 2g

Protective Body: Print Time ~ 20min, Weight 2g

Some sanding may be required to remove excessive material that may prevent the spindle being inserted partially or fully and similarly with the inner surface of the body to enable the magnets to fit.

Insert the cylindrical section of the spindle into the centre hole in a disc magnet.

This should be a tight fit, if its a loose fit a little adhesive putty (tacky), wrapped around the cylindrical section of the spindle prior to insertion will fill any small gaps between the spindle and the inner surface of the central hole

Optionally, around the cylindrical section wrap a layer of tape or apply a little glue.

An alternative spindle build can be accomplished fashioned from quick setting epoxy putty or a wooden dowel, rougly fashioned or machined from wood, plastic or metal into a shape similar to the 3D printed spindle.

Carefully, bring the second disc magnet in close contact with the first magnet such that they are magnetically attracted to each other and stick together.

I noticed that the ceramic magnets dimensions do vary a little even within the same batch of magnets therefore, you may have to select a matching pair that both fit within the protective body.

Push the magnet and spindle combination into the protective body.

This should be a tight fit, if its a loose fit a little tacky wrapped around the circumference of the disc magnets prior to insertion will fill any small gaps between the magnets and the inner surface of the protective body.

An alternative protective body can be applied around the circumference of the magnets by wrapping a layer of tape or inserting within heat shrink tubing.

If using heat shrink tubing and a heat gun do not apply prolonged excessive heat* as this may damage the magnets should they fracture, better to apply localised heat in small areas quickly with a soldering iron or similar which allows the heat to dissipate and cool between application. *Refer to the manufacturers operation and safety recommendations.

Apply some tacky in the central hole in the disc magnet and press in the ball bearing.

Remove any excess material and assembly is complete.

Static Spinning

Stack two disc magnets on top of each other and mount them with tacky, tape or glue centrally to the back of a plastic base (plate, tray or sheet of plastic), with a thickness of ~5mm. Too thick a sheet and there will be too little attractive force between the magnets and the spinner. Too thin a sheet and there will be to much attractive force between them preventing spinning. Some variation in thickness will also be dependant on variation in the magnetic fields.

If you do not have a ~5mm thick plastic base, thinner sheets may be stacked to achieve the required thickness.

Two magnets attached to the sheet with the combined separation created by the sheet and ball bearing creates the right balance of forces to maintain the spinner in place even when inverted.

Hold the spindle of the spinner between index finger and thumb and perform the action as if clicking your fingers. This will both spin and release the spinner.

The spinner will be attracted to the magnet at the centre and continue to spin for a period of time.

Some practice may be required to initiate the spin whilst positioning the spinner close to the magnet, if released too far away the spinner is pulled in to rapidliy and stops the rotation.

During the period whilst the spinner is spinning pick up the plate and with smooth movements hold it vertically or invert it horizontally and back to the horizontal position. The position of the spinner will remain horizontal relative to the surface of the base on which it is spinning. Whilst remaining relatively stable and still spinning.

Remote Control Spinning

An alternative approach dispenses with the magnet under the plate and transfers this to your hand.

With the spinner rotating wave the magnet in your hand over the spinner.

Depending upon the orientation of the magnet it will either attract or repel the spinner, in either case you can manipulate the position of the spinner without direct physical contact.

Free Spinning

No external magnets are used in this mode, simply get the spinner rotating and see how long it continues.

Rotational Times

Maximal rotational times are evident in Remote and Free spinning modes >3 mins whereas Static Spinning is in the order of <30 secs.

Further activities.

In the earlier step (Background), system losses were raised.

How can some of these effects be minimised.

Use the spinner on a hard surface that does not deform due to mass and friction. Tempered or laminated glass rather than plastic. This can be applied to all the spinning modes.

Another way to reduce the impact of friction is to reduce the effect of gravity, simply by inverting the spinner such that it rotates upside down. The effect of which will be to reduce the friction at the point of contact as gravity is pulling the spinner away from the base rather than pulling it towards it. This effect can be readily observed by inverting the base when the spinner starts to wobble in the non inverting mode the stabilisation only adds a fraction to the overall rotational time but is clearly evident.

Experiment and have some fun.