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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.

Best Parachute Mechanism

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LamdinRockets
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Best Parachute Mechanism

Post by LamdinRockets » Tue Apr 03, 2018 5:53 pm

Hi,
Looking for a tutorial to make a reliable parachute mechanism for a class D rocket, any recommendations?



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anachronist
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Re: Best Parachute Mechanism

Post by anachronist » Fri Apr 06, 2018 12:26 am

Gosh, there are many ways to do this. I've been dabbling with a mechanical mechanism that senses when the rocket is falling nose-down -- just drawing so far, haven't built it yet (it needs some 3D printed parts). I've been using an Eggtimer altimeter controlling a micro-server that pulls two pins to release the nose cone. There's a similar concept mechanism in this tutorial: https://www.youtube.com/watch?v=vqTKXXpD9IU -- and there's a side-deploy mechanism described here: https://www.youtube.com/watch?v=UnwP3YXOn-I



LamdinRockets
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Re: Best Parachute Mechanism

Post by LamdinRockets » Fri Apr 06, 2018 7:26 pm

Thanks.

I have come up with an idea similar to the one seen in the second video you have linked, except involving an internal release as opposed to the elastic band around the outside. Additionally my system would involve an arduino, an altimeter and a servo. However my concern is the weight of the batteries needed to power the arduino; I think 2 AAAs would be fine but I'm unsure, I can't seem to find a concrete answer on it.



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anachronist
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Re: Best Parachute Mechanism

Post by anachronist » Fri Apr 06, 2018 8:05 pm

Look for posts by the current class D record holder. That rocket uses a wind-up Tomy timer that releases a rubber band, and it's all internal.

You need sufficient power for your altimeter and the servos, as well as the servo controller if your altimeter doesn't have it built in. 2 AAAs won't do it. Some altimeters take a 9V battery. You generally need lithium-polymer (LiPo) batteries. Lithium batteries are light. Mine is a 7.4V LiPo. You can see a picture of my battery + servo + altimeter in this post: viewtopic.php?f=5&t=2994&p=19370&hilit=eggtimer#p19350 -- I recall that battery is about 15g.



LamdinRockets
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Re: Best Parachute Mechanism

Post by LamdinRockets » Fri Apr 06, 2018 8:13 pm

I'll have a look through the forums, can you recall his handle?
Apologies I meant accelerometer not altimeter. 15g would be absolutely ideal i'll try and locate one.



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anachronist
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Re: Best Parachute Mechanism

Post by anachronist » Fri Apr 06, 2018 10:06 pm

Handle is Retrotec29. See his class D submission at viewtopic.php?f=24&t=2996 which has some nice pictures of rocket details. There's also a video further down showing a parachute deployment test.



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