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note that the human body is a good absorber of stray RF fields, so this sensor should be a good people-detector

It's simply a Phototropic BiCore driving two small motors

I had to add resistors across the motor leads to slow them down! I got this idea from Ben Hitchcock's Fred Troubleshooting Page -- "D) If the motor fires strongly once..."

It is powered with two 3.3F Goldcaps. They can be charged in a few seconds. When they are charged, MAXIBUg gets "afraid" of light, and wanders of to go to play "in the dark". After a while, about 20 seconds (depending on the current used by the two motors ), the power has dropped, and it wants to "eat". It gets light attracted, and will turn and go to the light. When it gets there, it will recharge and still will be atrackted to the light until it reaches a trigger voltage , at which it gets "afraid"of the light again. This will go on all day until someone turns off the lightsource. While doing all this it also will backup when bumping into something.

Because of the "on-off" output of the first schmitt trigger, the inputs for the LDRs will switch. That's why it gets light atracted -light afraid. This also means that you cannot use IR diodes (like SHF205). You have to use LDRs !

Motorcycle lead acid batteries work great for larger low performance type robots. They are great for solar power robots too.

lead acid batteries have the serious problem of being very large and heavy, need to always be kept charged, and do not have the high discharge rates as the more modern batteries.

They have low power capacities, are heavy, have trouble supplying large amounts of current in short time periods, and get expensive to constantly replace

34164s are undervoltage sensing circuits ("voltage supervisors") designed for use as reset controllers in portable microprocessor based systems. We use them as 3- or 5-volt triggers (here, 3 or 5 fills in the "*" of the part number above), as the heart of the Chloroplast solar engine design.

To use a photodiode in its photoconductive mode, the photodiode is reverse-biased; the photodiode will then allow a current to flow when it is illuminated.