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 chimney.

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 frame.

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 finally arrived:

These pictures are really bad, but they give you an idea of how deep it was:

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 see, and...

...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!