A robot isn't going anywhere without juice. Your body uses a complex process of breaking down food into chemicals that it then converts to energy for powering muscles, organs, and other systems. In robots, a number of different substances are used to give a robot its get-up-and-go. The most common are electricity (from AC wall current, batteries, and solar power), air, and liquid. Let's take a look at each of these. Caution
The majority of mobile robots consume battery power. These batteries process chemicals, either wet or dry, to create an electrical current that can be sent through wires to power actuators, sensors, and on-board controllers. Since batteries are such a common form of robot power, we should take a few minutes to detail some different battery types:
Although battery power is extremely common in robots, it's not the only source in town. No amount of pouring battery juice into a hydraulic or pneumatic leg or arm is going to make it move. These actuator systems get their energy from liquid and compressed air. Again, like the cylinders themselves, the "circulatory systems" to power these two technologies are nearly identical. You have tanks that hold the liquid or air, strong flexible tubing to deliver the material, and a dizzying array of fittings, couplers, valves, pressure gauges, and other "plumbing" parts.
For true robot autonomy (or any other type of power autonomy, for that matter), nothingbeats the big bright rays of our closest star. Solar-powered robots use what are calledphotovoltaic cells to covert the sun's radiation (photons) into electrical power (electrons). Although this is a miraculous feat, it's also an extremely inefficient one. Only a small percentage of the energy that reaches the solar cell is actually absorbed and converted into electrical current (the rest is lost as heat). To be able to use this current, it must be stored up and then accessed when there's enough of it to do anything useful.
Some robots (like the Mars Sojourner) use batteries for storage, whereas other types of solar-powered robots, such as many robo-critters, use capacitors to store up their energy. We won't get into capacitors here (see the "Thumbnail Guide to Electronics" inChapter 6), but basically a capacitor is an electronic component that dams the flow of electrons. Eventually, that dam breaks and the stored electrons race ahead through the circuit. This storing and dumping of the electrons can be controlled further with electronics. Using a solar cell and capacitors (and other support electronics), one can make what's called a solarengine, a free, always-available (while the sun shines, anyway) power source. Of course, since the cells deliver slowly accumulating power, robots of this type live a manic-depressive existence of bursts of energy followed by languorous sunbathing. And while most robots have to be weight conscious ("Do these gearboxes make my hips look big?"), solar robots need to be obsessive about it.
There are other, more exotic, power systems for robots being experimented with. One of them involves bots that actually eat! Dubbed gastrobots, these robots would have a gastric system that can break down sugars and starches in food and convert them into usable power. Imagine what a boon this would be for autonomous robotics. There's even a Gastrorobotics Institute at the University of Southern Florida (www.gastrobots.com). The Institute's director, Dr. Stuart Wilkinson, coined the term.
Another extremely promising new power technology, for robots and just about everything else, is the fuel cell. A cousin to the conventional battery, a fuel cell produces electricity through an electrochemical reaction. But unlike a battery, fuel cells use hydrogen (the most abundant element of Earth) and oxygen, and will continue to produce power as long as there's fuel available. Batteries need to be recharged. Besides not running down, fuel cells weigh a lot less than batteries (for comparable power delivered), are much more power efficient, and are, overall, better for the environment. There are problems with fuel cells. Hydrogen might be abundant, but getting it into a form that can be used by the cell takes processing, and a good hydrogen source such as methane, propane, or natural gas.