Theresa attends ITP

Sustainable Energy: MIDTERM

Posted on March 26th, 2008 by Theresa Ling.
Categories: Sustainable Energy.

The Energy Harvesting See-Saw
Theresa Ling, Drew Burrows

The Problem

In our discussion of kinetic energy harvesting solutions, Drew and I both found an unfortunate trend in the existing energy generating devices: if human powered, most solutions are solo operations and while virtuous, not very fun. In essence, they feel like work. How, we wondered, can we strike upon a solution that is social, cooperative, and fun?

The Solution

We came to the see-saw after some false starts in other areas, but settled on this device because:

a) it uses the strength and weight of 2 people

b) it has a well defined and understood range of motion

c) they’re loved by children for a reason: they’re fun (when was the last time you played on a see-saw?)

In creating our prototype, we made an adult-sized see-saw with a larger range of motion than those typically designed for playgrounds. This was achieved by raising the height of the fulcrum point to allow the plank to rise and fall an additional few degrees. This addition, we found, made a substantial difference in the voltage output of the motor. The rise and fall of the plank turns a flywheel-belt mechanism to turn the motor, which is a DC gearbox motor. We built a very simple circuit that essentially fills a small 2200µF capacitor on both turns of the motor through the addition of a bridge rectifier. For our prototype, we have 2 indicator LEDs that are being powered directly by the opposing motor turns and 1 more that is taking voltage from the capacitor.

Energy Analysis

With the components we currently have, we calculated that the observed power of our mechanism is 0.0014 W/s. Given a larger motor with a higher gearing ratio and/or more torque along with a much larger capacitor, this device could be much more efficient and powerful. In our next iteration of this project, we’ll look into these possibilities.

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