The chimney claw project
One year, my parents realized that there was a bird's
nest down their chimney, at the very bottom. You could hear the chirps from
within the kitchen. Eventually, the chirps stopped, meaning that the
young birds were either dead, or had managed to fly all the way up through the
chimney on their maiden flight.
Let me give away part of the ending: There were no dead birds in the
Once the chirps had stopped however, my parents noticed that the kitchen fan
did not work efficiently anymore. The chimney-sweeps suggested that the best
thing to do would be to basically rip out and replace the entire chimney;
obviously a very expensive approach. I was a newly graduated software engineer
at the time, and had recently taken a course
in mechatronics, so I suggested (and constructed) something quite different:
What you see is a mechanical claw, somewhat larger than a human hand. It
consists of a servo (a motor combined with an angle sensor), some gears and the
actual claws. There are also some extra bright, white LEDs mounted on the
The claw hangs from a long cable, providing power and a control signal to
the servo. At the other end of the cable is a plastic box with a power switch
and a knob (actually a cog-wheel) on it. By turning the knob, you make the claw
open and close. Inside the plastic box are batteries and a programmable micro
controller, whose job it was to continuously figure out what position the knob
was in, and report this down the line to the servo.
This is what it looks like with the LEDs switched on:
So, having designed and built this contraption, the moment of truth had
These pictures are really bad, but they give you an idea of how deep it
Success! Lots of rubbish (or building material, if you're a bird) was
brought up. The claw went down and up again several times, but the first two
rounds brought up the bulk of it all.
However, it also became clear that some screws had loosened, making two
parts come off the claw. They were small parts, but still, when you go on a
mission to take things out of a chimney, you don't want to end up having
put stuff into it.
We did come up with an idea, though. The lost parts were made of metal, you
...my parents found a magnet and a long piece of string. After a bit of
fishing we had gotten both of the lost claw pieces back:
So there you are. The story about the chimney claw. And as a matter of fact,
the kitchen fan did work efficiently afterwards!