A little solar powered pendulum that I made a few years back. It uses a very simple circuit with just 2 transistors, a couple of resistors, a diode and some capacitors. Power is supplied by a two calculator solar panels wired in parallel for faster charging. The power is dumped into a coil which repels a magnet (disguised by some old brass gears) hanging from some fishing line. As the magnet swings back towards the coil the EMF generated lights a red LED in the top post and the power from the capacitors is dumped into the coil again giving the pendulum a little kick, forcing it higher.

Video, more pics and the schematic after the jump.

Pendulum swinging past the driving coil

The circuit is based on the following Solarbotics schematic that I found.

A view showing the LED and solar panels

Detail view of the pendulum gears

The messy guts of the thing

Close up of the rats nest (messy) circuit inside the box

For a start, most BEAM robots can be assembled out of mostly junk parts. Even if you have to buy new parts, there is usually a very low component count for each robot, making each project cheap.

For this project I wanted to make a small flower that responded to light in some way, using only components that I already had to hand. This is what I came up with:

Components used were as follows:

• Panasonic BP-242221 Solar Panel
• Pager motor
• 0.047F 5.5V Capacitor
• 1x 1K Resistor
• 1x 100K Resistor
• 1x 220K Resistor
• 1N4148 Diode (or similar)
• 2x 2N3906 PNP Transistors
• 1x 2N3904 NPN Transistor
• An empty beer can for the petals
• The base of an old PP3 battery for the stand
• The wheel of a small toy car used to mount the flower to the motor
• Wire for connecting components
• A glue gun & plenty of glue

When the flower is exposed to light the solar panel is charging the storage capacitor. As the light level drops off, the drop in charging current triggers the circuit and the energy stored in the capacitor is dumped into the pager motor, spinning the flower. In practice this means that when the sun is out the flower is charging, then as it is covered by clouds the charging current drops and the flower spins very rapidly.

Below is the schematic for the flower. It is based on the ‘Type 3 Solar Engine‘ design by Wilf Rigter. I didn’t have the same transistor to hand, but as with most things in the BEAM world, parts can be substituted for ones of a similar type with little effect on the final performance.

The components were free-formed using the ‘rat’s nest’ construction method. This doesn’t result in the cleanest finish (not in my hands anyway) but it does allow for a small form

A glue gun was used to secure the components and the bottom of an old PP3 type 9V battery was used as a support to keep the flower standing up

The flower was made out of an old beer can. Layers of petals were cut out in descending size and then stacked and hot-glued together.

This version was more of a quick prototype that a work of art, as you can tell.

I found that the wheel of a small toy car was a perfect fit onto the axle of the pager motor. This provided a nice flat surface to glue the flower too.

Here’s a video of the flower in action