This tiny little bot is my favourite. Very small and IMHO well constructed. Completely made from scrap. It Will fit in the 5x5x5 cm cube.
Parts: 74hc240 IC, solar cell from wasted calculator, few capacitors, 2 accus and most important: LED :))
Function: all my bots in the cawtbots series have no explicit function. Or should I say that the function is purely decorative. This one doesn't even move. It blinks at night. No batteries needed. Solar cell charges the NiMh accus through the day. Voltage drop in the dark and the process reverse, LED and IC are powered, voila: a blinking beacon bot is born. Works until there is some power in accus. When the daylight return the cycle is repeated. Endlessly.
Construction: made in the tricky freeformed style. Soldered with no PCB (printed circuit board). You can see that wires are kept as straight as possible. Could be hard to achieve.
Possible improvement: all the soft colored wires shall be replaced by unisolated straight line wire. This would add to very cool retro cyber thrashy look. Just a wishful thinking ...