The BEAM Circuits Collection is a
I used to oscillate, but now I've
Storing energy for a rainy
At the heart of most solar-powered robots is a circuit
called the solar engine (variously called Solar
Engines, solarengines, SEs; a.k.a,relaxation oscillators).
The purpose of a solar engine is to act like a power
"savings account" -- a small trickle of incoming energy is
saved up until a useable amount is stored. This stored
energy is then released in a burst, in order to drive some
useful (if only sporadic and incremental) work.
The solar engine has a number of advantages:
- A solar-powered robot can be made to work, even in
relatively-low light levels.
- Solar cell size is minimized
- Saves money
- Saves weight
- Allows room for the solar cell to be
There are four types of solar engines to date:
- Type 1 - voltage
controlled trigger. This is by far the predominant form
of solar engine, since they are "efficient enough" for
most uses, and pretty simple to build.
- Type 2 - time
controlled trigger. These aren't terribly efficient, but
are handy for 'bots that need activity at specific
- Type 3 - charge curve
differentiated (i.e., it triggers when the charge rate of
the capacitors slow down). These are theoretically the
most efficient, though type 3 designs are still in their
- Nocturnal -- These
solar engines charge up when it's light, and discharge
(i.e., power a load) when it's dark.
For more information...
Ivar Thorson's writeup on solar engines
(particularly handy since it includes efficiency
comparisons for various designs) is here.
The excellent BEAM-robotics-Tek writeup is
Ian Bernstein of "BEAM-Online" fame has a
writeup on 1381-based solar engines here,
and a tutorial on how to free-form this kind of