Water Release Mechanism - HELP!

I've been racking my brain trying to figure this one out, and thought I'd ask you guys.

I'm building a project which requires the release of a tethered "buoy" once this sinkable object hits the water. I know I could use a mechanical release - a water sensing probe that trips a servo release - but I would rather keep it really simple, and use just chemistry and/or physics to do the work, and somewhat quickly, within a minute or two.

I'm thinking that something must dissolve, expand or contract quickly when in water so that whatever is holding the buoy to the sinking object releases, and the buoy just floats to the surface.

Making a toilet paper "fuse" has come to mind, but I was hoping for something more solid. I considered salt (as formed into a salt lick) but because it's so dense would take a long time to dissolve. Sugar cube seems too fragile?

Any thoughts would be appreciated!

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Toga_Dan24 days ago

iirc, Edison tested thousands of filaments before finding one that worked well. if you Cruise the supermarket, it should be possible to find a dozen possibilities. aspirin? Noodle? Starch? dried potato?hard candy?also, Check recipes. how do you make hard candy? how do you make cotton candy? what about a cookie? us know your results, this might be transferable two other things.

ilpug27 days ago

What temperature is the water going to be? And does the mechanism need to be re-attachable or is it a one-shot disposable kind of thing?

PatrickA117 (author)  ilpug27 days ago

It will be in water less than 80F. It can be one-shot, though multiple use would be better..

Hmm okay. The more I think about it the more I like Caitlinsdad's idea of some kind of dissolvable tab. They are cheap and you can make a little holder that uses the tab as a sort of key to hold the thing in place.

Also, you could make something that operates a bit like the float valve in a toilet: have a little cylinder on the bouy with a tiny hole in the bottom that lets water in at a slow rate. As the cylinder slowly fills, a little float rises with the water level, eventually reaching a certain height and triggering some kind of little release catch. I'm envisioning maybe a length of PVC with a ping pong ball in it, which triggers a mousetrap-like system when it gets to the right spot. This seems entirely reusable and easy to tune to get the right time-to-release.

PatrickA117 (author)  ilpug26 days ago

The problem with a dissolvable tablet is ambient air moisture; I left an alkaline seltzer tablet out for only an hour, and it started to get soft.

You could candy coat the tab. So what are we doing here, sea bass or lake trout contraption?

salt or freshwater does make a difference two solubility of tabs regardless of their composition. good question caitlin's dad.

Toga_Dan24 days ago

what does the airline industry use?are there water activated buoys, rafts, or inflatables?

Toga_Dan24 days ago

what is edible underwear made of? cotton candy? What is its tensile strength?

caitlinsdad1 month ago

Alka seltzer tab. Good luck.

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