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The Photovore

Photovore

Build the Photovore, a light-eating robot! Here are the circuit diagrams, assembly instructions, and the parts list. There is also an animation in Javascript of the prototype in action. If you don't have Netscape 3.0 or higher, you can still see the animation fairly well as a 'moving gif' (232K).

Robots are scarce. You rarely see them in the street. Those that earn their daily bread work in large factories and laboratories. They are stupid machines. For everything they do, they need scripts describing every motion in precise detail. So they aren't real robots, because intuitively we reserve that term for a mechanism able to carry on by itself, without us determining every action.

Designing a real robot has proved to be very difficult. So far, none of the experimentals is able to safely cross a busy road or vacuum any house it enters. A robot clever enough to do such things may well remain out of reach for quite some time. The Canadian roboticist Mark Tilden thinks it's a good idea to start with building `wild' robots, machines that look after themselves and remain active for many years without needing their owner's helping hand.

Wait until a robot has learned to take care of itself. Then put it to work, domesticate it. Three `laws' describe the robot that Tilden tries to create:

  1. A robot must protect its existence at all costs;
  2. A robot must obtain and maintain access to a power source;
  3. A robot must continually search for better power sources.

The surest source of energy for an electronic robot is sunlight. An electronic photovore (light-eater) has an advantage over living nature, because solar cells convert light directly into electromechanical energy, whereas biological life needs a complex chemical interstage. And a robot has few natural enemies - it is not edible. This allows even very simple robots to remain active for a very long time, stubbornly searching for a better place under the sun.

A small robot, eating nothing but light. Would that be possible? It is easy enough if a rechargable battery stores the energy in chemical form. Rechargables and electric motors go well together. Unfortunately the robot would spend most of the day `sleeping'. In Dutch daylight - that is, under a heavy overcast - the little solar panel supplies about 2 mA at 3 V, say 5 mW. Using two 30 mAh NiCd cells that allows about half a charge per day, if the sun shines now and then a full charge is possible. But the most efficient motor I could find needed at least 15 mA to do anything, so it would use up an entire day's light within two hours.

The 1.6" x 3.1" solar panel is a Panasonic BP-378234, nominally 3.2 V. solar panel

Electric clocks use much less power. With a small modification you can accelerate their time considerably, and they are quite cheap. I bought a simple clock intended as a replacement part for about four dollars. The stepping motor was disconnected from the circuit inside the clock. Instead the oscillator shown was used to drive the stepper. Gradually increasing the frequency made the seconds hand ultimately do over 17 revolutions per minute. Faster running is possible, but then the stepper will just as easily turn in the wrong direction, which would rob the Photovore of its sense of purpose.

oscillator diagram The HCMOS inverters, the 100N capacitor and the variable resistor together form a square-wave oscillator, which itself uses almost no power. The second capacitor converts the square wave into pulses for driving the stepping motor inside the clock. Its value depends mainly on the stepper specifications.
An explanation of the abbreviations is here if your need it.

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