Introduction: Rotellino - Battery Free Contactless Bike Light

About: I am a lazy maker. I like electronics, 3d printing, fixing things and recovering mechanical and electronic components from things that don't work.

Rotellino is a cheap DIY bicycle light, simple to build and battery free.

Rotellino creates electricity almost frictionless because it uses the variation of the magnetic field generated by the wheel rim (Eddy current) to make a rotor rotate with 6 neodymium magnets and generate the current needed to power 2 LEDs.

For this project I was inspired by Magnic Light and Stonioni

Step 1: Materials and Tools



  • Soldering iron
  • 3D printer
  • Cutter
  • Dremel (optional)

Step 2: Prepare the Relay

We need to extract the coil from inside the relay and remove all the plastic and metal parts that we don't need.
The process is simple and done with common tools as shown in the pictures.

Step 3: Add the Leds

Solder the LEDs to the relay as shown in the pictures to fit well into the light housing.

Remember to connect the LEDs with reverse polarity as shown in the circuit drawing.

Step 4: 3D Print!

Download files from thingiverse.

There aren't special considerations for printing.

I used .25 layers at 50mm/s speed. The printing takes less than an hour and a half.

Step 5: Put It All Together!

Assembly is simple.

Remember to insert the magnets into the rotor with alternating polarity as shown in the drawing and video.

Step 6: Installation

Mount the light to the fork with a cable tie. I used a piece of red rubber to make it stick better.

Use the 2 joints to ensure that the rotor is 2-3 mm from the rim. The rotor must not touch the rim.

To figure out if the distance and position of the rotor is good, try turning the wheel and see if the rotor turns and the LEDs light up.

Step 7: Working Test

If well regulated Rotellino powers up between 5 and 10 Km/h. It emits a good amount of light for urban use of the bicycle.

I have been using it on a daily basis for about three months without any problems.

Soon I will upload a video with the bike in motion!

Any suggestion and advice to improve the project is welcome.

Support me and my projects at this link

Magnets Challenge

First Prize in the
Magnets Challenge