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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

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What's a pyrotechnic squib?

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anachronist
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What's a pyrotechnic squib?

Postby anachronist » Fri Jun 30, 2017 11:43 pm

Regarding the safety rule at http://www.wra2.org/Water_Rocket_Safety_Rules.php which says "Reco.very system cannot contain black powder, fireworks, or pyrotechnic 'squibs'."

What is a pyrotechnic squib? Is that like an Estes pyro engine igniter, which consists of a wire that heats up to ignite a coating on it, which in turn ignites the engine?

What about a very thin wire that simply melts in a fraction of a second? Would that count as a "squib"?

I ask because I was in a conversation with the Eggtimer altimeter folks about water rocket recovery possibilities, using the onboard altimeter's deployment signal. The Eggtimer's deployment signal can be programmed to supply full battery power for as little as 1 second, which is enough to drive a servo controller. For that matter, you don't even need a servo, just a motor and a gear would be lighter. Or a simple hand-made solenoid actuator may be even lighter. Then he asked, why not just use that battery power to melt a very thin wire to release the nose cone? He clarified he wasn't talking about a rocket engine igniter, just a thin wire (like from an electronics fuse) that melts quickly.

Would fuse wire be considered a "squib" according to the competition rules? I could even encase it in a small glass tube so the melting material never touches anything.

A side question is, are the deployment signals built into some altimeters allowed for deployment systems on water rockets and still be compliant with competition rules?
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Re: What's a pyrotechnic squib?

Postby anachronist » Wed Jul 12, 2017 4:15 pm

Any decision on this?

It occurs to me that the weight advantage may be minimal, since I'd have to come with some sort of latch that prevents the melting wire from touching anything except the latch itself. The length of wire subject to melting would likely be a millimeter or two, though.
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Re: What's a pyrotechnic squib?

Postby WRA2 » Wed Jul 12, 2017 9:51 pm

anachronist wrote:Regarding the safety rule at http://www.wra2.org/Water_Rocket_Safety_Rules.php which says "Reco.very system cannot contain black powder, fireworks, or pyrotechnic 'squibs'."

What is a pyrotechnic squib? Is that like an Estes pyro engine igniter, which consists of a wire that heats up to ignite a coating on it, which in turn ignites the engine?

What about a very thin wire that simply melts in a fraction of a second? Would that count as a "squib"?

I ask because I was in a conversation with the Eggtimer altimeter folks about water rocket recovery possibilities, using the onboard altimeter's deployment signal. The Eggtimer's deployment signal can be programmed to supply full battery power for as little as 1 second, which is enough to drive a servo controller. For that matter, you don't even need a servo, just a motor and a gear would be lighter. Or a simple hand-made solenoid actuator may be even lighter. Then he asked, why not just use that battery power to melt a very thin wire to release the nose cone? He clarified he wasn't talking about a rocket engine igniter, just a thin wire (like from an electronics fuse) that melts quickly.

Would fuse wire be considered a "squib" according to the competition rules? I could even encase it in a small glass tube so the melting material never touches anything.

A side question is, are the deployment signals built into some altimeters allowed for deployment systems on water rockets and still be compliant with competition rules?


A "squib" is similar to a firecracker and are used by pyro rocketeers to deploy parachutes. When the competitions were first designed 15 years ago, parachute deployment was a big challenge. Since fireworks are not legal everywhere, it was decided that teams living in areas where fireworks were easily obtained would have an unfair advantage.

As far as electronic deployment signals are concerned, they are allowed and are usually used to trigger servos as part of a deployment system.

I also see no reason that a "break wire" as you are describing cannot be used either.
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Re: What's a pyrotechnic squib?

Postby anachronist » Thu Jul 13, 2017 12:53 pm

WRA2 wrote:A "squib" is similar to a firecracker and are used by pyro rocketeers to deploy parachutes. When the competitions were first designed 15 years ago, parachute deployment was a big challenge. Since fireworks are not legal everywhere, it was decided that teams living in areas where fireworks were easily obtained would have an unfair advantage.

OK, that makes sense. I guess nowadays it's called an ematch or electronic match. To me it makes sense to disallow them, not because of an unfair advantage, but because of the risk of melting or weakening critical plastic components in a plastic bottle rocket -- like the parachute or pressure vessel.
WRA2 wrote:I also see no reason that a "break wire" as you are describing cannot be used either.

Thanks for the clarification. With servos available weighing just 4g nowadays, and some altimeters like the US Water Rockets LaunchPad AlTImeter and the Eggtimer altimeters having built-in servo controllers, I see it as a challenge to come up with a lightweight and safe melt-wire mechanism. But it does open up some possibilities. I'm sure I can come up with something that weighs less than a Tomy timer mechanism or an arrangement requiring a separate servo controller + servo.

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