Donut Motor

I hope this DIY Donut Pulse Motor project inspires more people, here at Instructables, to make the underlaying idea to a common quest.

That idea is to make a small motor that can run for 1 lifetime; say 100 years. Imagine the many obstacles that you have to take:

What energy source can last for a lifetime?

What about wear in the motor construction?

What about minimal energy consumption?

How to measure long duration behaviour?

The Donut Motor runs on a 3V - 235mAh lithium cell with a current of 13uA for about 2 years. This duration is only calculated and not tested in practice. This is a great winter project; it is challenging, instructive and fun to build in some hours. When I enter my Lab and see the Donut Motor running, without a sound, that’s magic.

The motor cosists of only a few parts:

1 - Stator; a torus in 2 halves to attach magnetic bearings and pulse coil.

2 - Rotor; a sphere from Styrofoam or ‘Blue Board’.

3 - Pulse air coil; scrapped from a relay, made with new terminals.

4 - Pivot; made from a spoke and sharpened to pointed ends.

5 - Bearing magnets and glass pieces

6 - Rotor magnets glued to the sphere in a balanced way.

7 - Breadboard with electronic components; see drawing.

8 - The right glue, utility knife and small screwdriver.

9 - A bottom plate with the Donut Motor support posts.

10- Watch the photo’s and stop the video for all the details.

The motor has 3 main parts to be made:
1 - The rotor is made of a styrofoam sphere with 4 bar magnets evenly distributed over the circumference of the sphere. The axis must pass exactly through the center of the sphere. Important is a well balanced rotor to avoid swaying in the magnet bearings. I took fast-drying hobby glue, (which does not dissolve Stryrofoam!), to stick the magnets to the rotor. The rotor diameter is 6 cm, the pivot is 70 mm long.

2 - The magnetic bearings are glued with the glass against the inside of the torus. The distance between both sides is 71 mm. The bearing ring magnet is attached with double-sided tape to the glass.

3 - The electronic circuit is mainly an air coil, scrapped from a relay with a 220V AC solenoid with a impedance of 14.000 Ohm. The circuit is build upon the breadboard together with the lithium cell. Watch the diagram. At the inside of the torus the coil is fixed, such, that the gap between the rotor magnet and coil is 1 mm or less. The torus is standing at 4 legs of wood. Keep magnets and iron objects away from the motor.

If you have bought and prepared all materials you can assemble and try out the donut engine within a few hours. After the glue is dry and the circuit is setup, you can start testing the motor. An oscilloscope makes it easy to tune circuit with the potentiometer to the most economical and clean setting, without oscillations. The capacitor of 100nF is to avoid this undesired effect. The diode or LED over the air coil is to take away the back emf. The LED light’s up a little with every pulse. The scope image shows in detail the puls shape with a pulse/pause ratio of about 1 to 2.5. Maybe this pp-ratio can be more economical.
Once the Donut Motor runs, you can enjoy the continuously rotating rotor. It seems that the transistor pin connection in the scheme is false, but I can tell you that it works. When the rotor magnet passes the coil it induces a small voltage. This opens the transistors for 40 msec and produces enough flux in the coil to push off the rotor magnets. Take care, the coil must produce a north pole at the rotor side. Success!

The Donut Motor is an ongoing project, with updates at my YouTube channel.