Double Spin Solar Pendulum




Introduction: Double Spin Solar Pendulum

About: Tinkerer from childhood on. After my retirement, together with my wife, fully committed to creative production. I prefer simple solutions for non-existing problems.

The name 'Double Spin' comes from the fact that the pendulum weight is rotating around a coil and also around its own axis. Normally you can expect that the weight goes back and forth. The reason of this rotation is because the weight hangs on a long needle with an extreme low friction suspension point. The weight consists of a magnet in horizontal position moving a few milimeter above a coil. Only the northpole triggers a pulse in the coil. Under the wooden platform direct beneath the coil is a very small magnet located. All this; magnetic field and electromagnetic pulse makes that the pendulum weight is double rotating and stays doing that.


  • Wooden platform 140 x 180mm and 20mm thick
  • Aluminium strip, total lenght 64cm, 10mm wide and 1mm thick
  • Mattress needle 10 inch long
  • Suspension point magnet 10mm high, 10mm round
  • Glassplate 10x20mm and 1mm thick
  • Coil from a 220V reduction motor 8.3K ohm
  • Weight made of 2 magnets 10mm high, 10mm round
  • Electronic parts, see drawing

Step 1: Video

Step 2: Construction of the Pendulum

The construction is quite simple. On a wooden board an arc of aluminum strip is made. See the drawing with the right measures. Use brass screws to connect this to the board. Connect the magnet and the glass plate with superglue in the middle of the top. Place the coil in the middle of the board, exactly below the top magnet. Make the weight with 2 magnets and a holder of copper strip so that this can be fixed to the needle. The lenght of the needle and magnet are such that the weight hangs 2mm above the coil. Connect now the electronic circuit.

Step 3: The Driver Circuit

The electronic diagram can not be more simple but it works great. When the northpole passes the coil an electric puls opens the 3906 transistor via a variable resistor. This opens the 3904 transistor; the coil gives a pulse back to the pendulum magnet and it moves away from the coil. With the variable resistor the pulse is made as clean as possible. The LED lights up by the back EMF and charges the supercap a little. Charging by the solarpanel happens via a diode because the low resistance of the panel could deflate the capacitor by night. The photo of the oscilloscope shows the pulse with some spikes. The capacitor may vary from 3 to 50F with a voltage of 2.7 or 3V. The solar panel is a 3V 90mA type. More voltage panel can only be used with a voltage regulator.

Step 4: Conclusion

When I enter my electronic lab I see this pendulum move in this very special way. It behaves like the rotor of a motor but also of a generator. A fast rotation of the magnetic weight induces power back in the coil. The driver circuit uses about 14 micro ampere. That is so little that it can run for weeks without solar charging. I use a supercap of 10Farad and this is always full. Just one hour sunlight a week will do. Success with building this continuous spinning device!

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    Question 11 months ago on Step 4

    Really like this, especially the simplicity of the circuit and the double rotations.

    Does this circuit self start or does the pendulum need to be pushed to get it going? I'm thinking of not bothering with the supercap as I don't mind if it only works in the light, but if it won't self start I might have to change my plan. I suspect it doesn't from the circuit, but I'd be grateful to find out first for sure.


    Answer 11 months ago

    No self start in this circuit. And yes the double rotation by a horizontal hanging magnet is my unique design. For a selfstarter pendulum you have to make a simple addition to the existing circuit. Take care, you need a stable powersupply to flatten the voltage input of the solarpanel. This circuit works within a narrow power range. Use a LDO of the right voltage. See my other pendulum project.


    Reply 11 months ago

    Thanks for your reply, all very useful information. I may just use the circuit type that gives a kick every now and then by reusing the insides of a cheap nodding solar toy. However, I'd prefer something like yours as it is building up the swing by reacting to it. I will definitely be using your magnetic pivot idea though, really clever, and I like your spinning development as well so will be using that also.
    Your other pendulum is also interesting because it doesn't take a lot extra to create a more interesting interaction and it's easily scalable, maybe with putting another passive pendulum to the other side?