Evolution of the raspberry

Mon, 12 Oct 2009

 Rasp 1

I'm doing a bit of development work. I fancy the idea of making a model that blows a raspberry. (I'm not sure if that is a UK only phrase – stick tongue out and blow making a rude sound.) I've tried a few prototypes and made a bit of progress!

The first attempt was a rectangular section tube, 20mm wide by 6mm deep. The tongue attached to the far end in the middle. It worked okay but was quiet. The second one (2) was a bit thinner and worked better but after blowing through it a few times the end got crushed (3) and it stopped working. It looks like it is important that air blows down both sides of the tongue, that's what makes it work.

 So, to ensure a smooth air flow I remade the tube, but this time, tapered. Again, the tongue is fastened at one end in the middle and is free to flap up and down. This one (4) didn't work at all! Thinking that the problem was that card tongue was too stiff I re-made it, this time with a paper tongue in a card tube. It worked! Problem was the rasp noise was too high pitched. I reckoned that the paper was light weight, and therefore, fast moving. Next step I made a tongue sandwich, most of it made from paper for flexibilty but with card glued top and bottom to the end. (diagram above) The extra weight slowed everything down. It works great. Just what I was after. I was going to make a video but ended up making school resources for my True Love and now its dark.

Tomorrow I'll be trying to connect the whole thing to a set of bellows. That should be worth videoing!