Water Bottle Rocket Launch Mechanism

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Introduction: Water Bottle Rocket Launch Mechanism

A simple and reliable release mechanism for water rockets can be built from PVC plumbing supplies and cable ties, as in the diagram. This will cope with pressures in excess of 100 p.s.i with safety.

Step 1: General Principles

An easily controlled release mechanism is shown, whereby the forces trying to drive the bottle upwards are directed downwards along the length of the cable ties, with only a very small component, courtesy of the bevels on the tie terminations, directed outwards against the retaining sleeve. The coefficient of friction for plastic on plastic is low and the actual contact area is reduced, because of the internal curve on the sleeve, such that very little effort is required to pull it downwards, well within the amount of force that can be supplied by a radio control servo, for example.

Step 2: Construction

The details are illustrated here. You may find it easiest to take a bottle to the hardware store and browse around to find bits that fit together without too much slack. The black 'O' ring is important in providing a tight seal otherwise the water will leak out as you pressurise the reservoir.

Step 3: Release

The outer sleeve is shown in the locked and released positions.

Step 4: Launch

Pump it up to 80 - 100 psi and pull the sleeve down to launch. A good trick is to get an unsuspecting person to do this from close range and they will be soaked by the escaping water.

Step 5: 3...2...1...WHOOSH!

Works best with the bottle between 1/3 and 1/2 full. Enjoy!

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    26 Discussions

    I actually find that between 1250 and 1400 millilitres of water at 80 psi is optimal for a 2 litre thruster plus a nose (smart water bottle with a tennis ball strapped to the end), and if using a different bottle, scale it up or down properly. Just opinion, but based on fact that these are my best results. (No i am not British, but it's a habit to spell it that way)

    2 replies

    Not a problem, I'm always glad to give advice and do my best to make sure my spelling is easy to read

    Outstanding!! I was starting to mess around with mouse traps as well as other homemade levers. Thanks!

    I have done 2 stage rockets with my science programs. I take a 2 liter bottle, add a cut off bottom to the top, such that it can carry payloads (best one is vegetable bags from produce isle of supermarket, with beans taped in 4 places to make a simple parachute) however, to make a second stage, i have kids make paper airplanes with unfolded paperclip in the mid section, such that you could launch it on a rubber band. then i attach a rubberband to the waterbottle rocket, add the paper airplanes, and launch. the rubber band stretches on accerleration, and launches to airplane or glider as the momentum from the stage one rocket fades. you can also just hook the paper airplane in the payload half top and see max time aloft of planes. I'll have some of this on my site in a few weeks. www.the-inventor-mentor.com terry murray

    yah. i found this site, but havent gotten around to making it.<br/>here's the link: <a rel="nofollow" href="http://home.people.net.au/~aircommand/howitworks_2.htm">http://home.people.net.au/~aircommand/howitworks_2.htm</a> <br/>

    Hey, thanks for that! Ingenious to the max. Obviously works but still quite complex....and heavy. Will certainly give it a go tho'.

    I have kinda an idea for multi stages, you could cut the bottle's bottom off then put another bottle inside, that and glue it so its airtight. Pressurize the top bottle first, then fill up the bottom bottle and pressurize that, but i dont have any ideas on how to get the second bottle going though. Or maybe you could have it so the only thing keeping the top bottles valve shut was the pressure from the bottom one, then when the bottom bottle is done the second one will go off, if you get what i'm saying. I dont know if it would work though. Good i'ble by the way.

    I think the answer will revolve around differential pressures somehow - as the pressure drops off in stage 1 it releases a valve in stage 2 which then accelerates on its own. Both stages will need to be independently pressurised tho'.

    This looks nice all put together like this but would really be helped by having a parts list and assembly instructions.

    Can you show how to make this? I've tried this using the pictures as a guide but it never works no matter how I change it.

    very good, very clear. The first picture is very good. Ive seen this design before, but this is the best one

    3 replies