Midterm project by Mary Fê, Maria Paula Saba, Xuedi Chen.

For our midterm project, we wanted to make a wearable/mobile system that produces energy either shaking or beating it.

First, we thought about using piezos, but they produced almost no current with high voltage peaks. Inspired by shake-lights, we proposed to build a shaking system with copper coil and magnet passing through it.

Our first attempt was a failure. It produced something around 0.06V (60 mV) and 4 miliAmps.

Problem was: the coil was too small. We needed a LOT more wire.

We tried other coils and started getting some more interesting numbers. The coil on the left in the first picture produced a bit more than 10V! The middle one 5V and the smallest reached 2.5V.

To calculate Power, we measured the voltage difference when charging up a capacitor. Doing the math, we reached the following numbers:

Starting voltage: 1.5V
Ending voltage: 6.5V
Capacitance: 4700 microF
Starting energy: 0.5 * (0.0047 F) * (6.5 V) * (6.5 V) = 0.0992875 joules
Ending energy: 0.5 * (0.0047 F) * (1.5 V) * (1.5 V) = 0.0052875 joules
Difference: 0.0992875 – 0.0052875 = 0.094 joules
Time: 3 secs
Power: 0.031 Watts

Our following step was to build a tube in order to get more out of the magnet movement. And then, the Harvest Shake was born! Enjoy!