The inspiration for this solar engine came from Mark Tilden, who invented the original solar engine. Mark is a prolific inventor who also began the BEAM technology. He is currently designing robots like the Robosapien for WowWee Toy Company. I liked the electrical function of Mark's solar engine so much that I decided to design my own solar engine.
The solar engine is an onboard power plant for BEAM type
robots, sometimes called living robots. The circuit is simple
in function. The main components are a solar cell, main capacitor
and a slow oscillating or trigger circuit. The solar cell charges
the capacitor, until a predetermined voltage is reached, where
the trigger circuit dumps the stored electrical power from the
main capacitor through the main load (usually a high efficiency
motor). The cycle then repeats.
Figure 1 is the schematic for the solar engine. Here's how it works. The solar cell charges the main 4700 uF capacitor. As the capacitor charges, voltage level of the circuit increases. The UJT begins oscillating and sending a trigger pulse to the Q1. When the circuit voltage has risen to about 2 volts from the main capacitor, the trigger pulse is sufficient to turn on the Q1. When Q1 turns on, this turns on Q2 the 2N3906 transistor through the 2.2K resistor. The 2N3906 keeps the 2N3904 turned on until all the store power in the main capacitor is dumped through the 2N3904 and the high efficiency (HE) motor. The motor spins momentarily as the capacitor discharges then stops. The cycle repeats.
The solar engine circuit is simple and noncritical. It may be constructed using point to point wiring on a prototyping bread board. A PCB pattern is also included for those who want a neat looking project.