Page 137 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 5 Mechanical and Electrical Power, Work, and Energy 117

a penny for the copper. A pair of electrodes like these inserted into a potato will generate
around 1V at a very small current (just a few milliamps). Individual bio-cells can be
added in series to generate higher voltage, and in parallel to generate more current. 4

Your basic LED needs about 10mA at 2V just to light up, so you’ll need a whole plate
full of potatoes to get enough power. As far as making things move, even tiny pager
motors won’t start spinning until you feed them about 20mA, and they want more
current as soon as you do anything with them (see www.solarbotics.com/products/
rpm2/ for an example). So to get enough power for a motor, you’ll probably need a
whole sack of potatoes, or better yet, a whole garden.

Humans
The simplest way we can create energy is to use our mechanical energy of movement
to create different kinds of movement. For example, hand-cranked mechanical toys
like those from the Cabaret Mechanical Theatre (www.cabaret.co.uk) in the United
Kingdom range from dancing goats to flapping owls. These are powered by only a
hand crank interacting with all kinds of gears, springs, and cams inside the wooden
mechanisms. We’ll discuss mechanical toys and kinetic sculpture more in Chapter 8.

Wind-up toys have been around for hundreds of years. They have springs or elastic
bands to store the wind-up energy we create and use it to make a bug crawl or a toy
car move. Modern ones from Kikkerland (www.kikkerland.com) and Z Wind Ups
(www.zwindups.com) are popular with kids as well as adults. The following section
talks about how you can use springs to store energy like in these mechanisms.

We can also use our mechanical power to create electrical power to use or store for
later in rechargeable batteries. Hand-cranked flashlights and radios have been around
for years to eliminate the problem of dead batteries, especially in emergency or
power-outage situations. Because of the low power requirements of LED technology,
about 1 minute of cranking can give about an hour of light on one of these flashlights.

The problem with hand-powered mechanisms is that it’s hard to create enough electrical
power to do much more than light a few LEDs. Luckily, our legs are built to convert more
energy than our arms or hands—after all, we do walk around on them all day. For
example, you can find bicycle-powered blenders at Fender Blender (www.bikeblender.
com) that will whip up a smoothie while you work out. Other companies are exploring