I think this is the only Lego-built flashlight that doesn't run on any batteries at all! First of all, you need to understand that when you turn a crank connected to a motor, the motor acts like a generator and creates energy. I used this energy to power 2 LEDs. The problem? I couldn't spin the crank fast enough to produce constant, consistant light. I fixed this by gearing up the generator (M-motor). Now when you turn the crank once, it turns the generator 14.5 times.I also increased comfort and stability with some well-placed parts. In the top picture, you can see my wire-control system. It is a little noisy, but lights well. Feel free to check out my other creations.