Alt-BEAM Archive
Message #06031
To: beam@sgiblab.sgi.com beam@sgiblab.sgi.com
From: Ben Hitchcock beh01@uow.edu.au
Date: Saturday, 11 September 1999 5:29
Subject: Re: Spark igniter
>>Hi
>>Today me and my friend built a potato cannon. For those of you that don't
>>know what a potato cannon is it's a large gun made out of PVC pipe that
>>shoots out potatos and uses hair spray for fuel. The igniter we used is
>>from outdoor grills and when the button is pressed a rather large shock
>>is produced (up to about 3/8"). I am curious where all the electricity
>>comes from because there are no batteries or anything. Anyone know how
>>these work? I know it's not really beam but it may an spark an idea for a
>>new preditor bot that shocks it's prey (already been discussed) or
>>something. Don't get get any ideas about mounting the gun on your human
>>seeking head though (interesting idea, any thoughts on how to make a head
>>seek humans?).
>
>The sparking device contains a piezoelectric material, a spring, and a
>weight. That's pretty much it. The way a piezoelectric material works is
>that it produces a voltage when you compress it, and also it will compress
>when you apply a voltage. So it works both ways. You may have seen a
>piezoelectric speaker already - they are those little flat brass speakers
>that you find inside cheap toys and greeting cards.
>
>Anyway, the way the sparker works is that when you press the button, the
>spring compresses, until the weight gets past the trigger part - and then
>the spring forces the weight to slam against the piezo material. This
>produces the voltage that you can see (and feel, if you're the recipient!).
>It produces a couple of thousand volts, but the duration is very short, and
>the current available is absolutely minimal. I would still be reasonably
>careful not to get too many shocks though - a shock like that if it occurs
>across your chest can cause your heart to lose it's rhythm. There is a
>critical part of the heart's rhythm (about 10% of a full cycle) where if
you
>get a shock, you can cause the heart to lose its rhythm. This is why at
BHP
>(Where I work) EVERY shock must be reported and your heart tested. Even
>little 32V shocks should be reported.
>
>So, I guess the moral is don't stick the terminals across your chest.
>
>PS. With the cannon, did you have a T-piece at the bottom to create a
>bigger expansion area, or did you only use the one straight piece of tube?
>
>Ben Hitchcock
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