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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.

parachute deployment just an idea

Discussion about deployment systems including altimeters, timers, air speed flaps, servo systems, and chemical reactions.
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andicirk
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parachute deployment just an idea

Post by andicirk » Sat Oct 11, 2008 4:23 am

this is just a thought i had this morning while drinking my coffee , ive had a look around at various parachute deployement systems and many of them use a timer or such .....

i was thinking that (correct me if im wrong) that glider pilots and other ppl who fly on thermals use an altimeter with a sound output one sound for going up one sound for going down ....(stay with me)

what if we used a spring loaded ejection system( bent piece of bottle inside the parachute door) and the parachute door closed using an mini electro magnet connected to the descending sound of the altimeter, this way the parachute would only deploy when the rocket is coming down,


i have no idea what this would cost or if this has been posted somewhere else before, and as i said at the start of my post this was a morning coffee idea..........



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Re: parachute deployment just an idea

Post by dongfang » Mon Oct 13, 2008 6:36 am

Hi,

Surely, altimeter controller deployment would be great to have! I think it might be as easy to make it bottom-up oneself as to build a circuit to decipher the sounds of an ultralight altimeter.

I wonder if any of the water rocket / RC model altimeters and / or "onboard computers" that are sold on the internet have provisions for that?

BTW, I think a normal small RC servo would be better than an electromagnet: The magnet must either be super-quality engineering, or it must be fed with quite a lot of current. The servo uses almost no current as long as it is not commanded to move, and it has lots of torque in both directions.

Regards
Soren



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Re: parachute deployment just an idea

Post by Tim Chen » Mon Oct 13, 2008 11:03 am

dongfang wrote:Hi,

Surely, altimeter controller deployment would be great to have! I think it might be as easy to make it bottom-up oneself as to build a circuit to decipher the sounds of an ultralight altimeter.

I wonder if any of the water rocket / RC model altimeters and / or "onboard computers" that are sold on the internet have provisions for that?

BTW, I think a normal small RC servo would be better than an electromagnet: The magnet must either be super-quality engineering, or it must be fed with quite a lot of current. The servo uses almost no current as long as it is not commanded to move, and it has lots of torque in both directions.

Regards
Soren
Mark and I did some tests with "rare earth" magnets. They are very powerful for their size and create a lot of force. We made an electromagnetic coil and discharged a 300V capacitor from an old camera flash into it and it fired the magnet off like a gun! There is a huge amount of force from this setup, but we have not figured out a nice way to charge the capacitor and switch the power to the coil when we want a deploy. Some kind of solid state switching transistor sounds like the answer, but we are weak on transistor theory.


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Re: parachute deployment just an idea

Post by dongfang » Tue Oct 28, 2008 10:02 am

Hey, if we are going to make an electric parachute release, I have an idea: Put a blue filter in front of a rearward-looking phototransistor. As soon as it sees the sky, it triggers. Or, even better, one transistor looking forwards and another looking rearwards. A simple op-amp comparator compares the intensities.

I will try testing a little around with my camera's light meter one day, to see if the sky is bright enough wrt the ground to make something simple and reliable.

Regards
Soren



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Re: parachute deployment just an idea

Post by Tim Chen » Tue Oct 28, 2008 4:16 pm

dongfang wrote:Hey, if we are going to make an electric parachute release, I have an idea: Put a blue filter in front of a rearward-looking phototransistor. As soon as it sees the sky, it triggers. Or, even better, one transistor looking forwards and another looking rearwards. A simple op-amp comparator compares the intensities.

I will try testing a little around with my camera's light meter one day, to see if the sky is bright enough wrt the ground to make something simple and reliable.

Regards
Soren
I've been playing around with a device called a "Magnetic Apogee Detector". It looks at the angle of the magnetic field lines of the earth to tell if it's pointing up or down. In my hand it works very reliably. I have not flown it yet but it triggers every time.


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Re: parachute deployment just an idea

Post by andicirk » Tue Oct 28, 2008 5:59 pm

I've been playing around with a device called a "Magnetic Apogee Detector". It looks at the angle of the magnetic field lines of the earth to tell if it's pointing up or down. In my hand it works very reliably. I have not flown it yet but it triggers every time.

thats a great idea ,lets hope it works ..........in flight



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Re: parachute deployment just an idea

Post by dongfang » Wed Oct 29, 2008 1:48 pm

Hi,

Way cool idea, the magnetic detector! I guess it runs on hall elements?

I had another idea for a mechanical system that should trigger even in ballistic flights (my multi stage flights never get very straight). The only flight characteristic required is some hard braking followed by some time with no or only small longitudinal acceleration.

Here it is. It is somewhat inspired by the Japanese system in the other thread, but it is built into the nosecone bottle instead of hanging on the outside. I don't mind flying around with a weight. My rockets are so light that some inertia would drag them higher up. Maybe one could adjust the thing by finding out how many (x1) g's the deceleration would be after burn-out, and then find a spring that is sufficiently compressed by a weight that is x1 times heavier than the one used in flight.

Regards
Soren
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Re: parachute deployment just an idea

Post by Tim Chen » Wed Oct 29, 2008 3:44 pm

dongfang wrote:Hi,
Way cool idea, the magnetic detector! I guess it runs on hall elements?
I don't know what the sensor is made of but it is a commercial part used in electronic compasses. It measures the magnetic flux lines of the earth and can tell the orientation that way. A simple comparator circuit is all that it needs to create a pulse when it deviates from vertical. It should work just as well in flight as it does on the ground. Several people have used this before and have had good results.


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Re: parachute deployment just an idea

Post by andicirk » Wed Oct 29, 2008 5:57 pm

i tend to like the idea of technological solutions but prefer the mechanical ones as they tend to last longer and are more acessible to the general public , piece of wire ,gravity, fishing weight etc , very zen

as things have more and more micro technology in them they become more disposable , its hard to bend a circuit bored back into shape

i might be saying this as well because this week my computer went down, ive been working on a citroen car( more technology in there than is really necesary) and my 20 year old truck (no computer based technology ), and i spent a lot less time each year on the truck lol,

r&d is important and helps us find solutions , but some times we look to far into a tech solution when a simple mechanical solution is maybe better



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Re: parachute deployment just an idea

Post by Tim Chen » Thu Oct 30, 2008 10:22 am

Here is a photo of the Magnetic Apogee Detector. The red L.E.D. is just an indicator for testing. It connects to the screw terminal bus where the signal is output. If the board is held vertical the LED is off, and if it is tilted to horizontal the LED comes on. We have a friend building a servo actuator from a microprocessor chip that will read the output and move the servo as soon as it sees the signal come on.
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Re: parachute deployment just an idea

Post by Andromeda » Fri Oct 31, 2008 8:46 am

Tim, nice looking circuit board you designed. Do you have the files to make the PCB that you can share?


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Re: parachute deployment just an idea

Post by Tim Chen » Fri Oct 31, 2008 10:40 am

Andromeda wrote:Tim, nice looking circuit board you designed. Do you have the files to make the PCB that you can share?
Sorry but I can't take credit for the design. I bought it from these guys this past summer: http://www.aeroconsystems.com/electronics/mad.htm and gave it to a friend to make the servo system. He's made a circuit board for the servo controller that hooks into the MAD board. I don't have his designs but I'll ask if he would send them to me.


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Re: parachute deployment just an idea

Post by Tim Chen » Fri Oct 31, 2008 3:13 pm

Here is the prototype MAD servo controller. It is designed to fin in a rocket as small as a T8 FTC. We have mounted it into a bottle cap so that can be slid in and out of a piece of T8 tube. T8 inside diameter is the same as the caps so they are used to hold the parts in place. The servo is mounted to another cap and uses a pushrod made from a large tie-wrap to eject the nose-cone.

We are preparing for drop-testing a crash test "dummy" rocket to see the best way to extract the parachute from the tight FTC. The rocket is just a weighted tube with fins and no electronics. We want to perfect the deploy without risking the electronics.

We have a few options:

1) Connect nose to the rocket with a streamer to create drag to pull the chute out from inside the nosecone.

2) Make a "clamshell" nosecone that is hinged and springs open when it is removed from the FTC and has the parachute stored inside. If there is not enough room in the nose for a parachute we will extend the nose with a section of T8 tube that will become the "clamshell".

3) The nose extends down one side of the rocket with a "door" that covers a parachute side-deploy bay with a spring loaded chute ejector. If we go this route we will possibly just glue the nose on and use the servo to unlatch a spring loaded parachute door.

Our perfect design would have the chute inside the nosecone 100% because we think that extra length is wasted space and weight and it also throws off the rocket stability. The more space efficient the deploy module is the better. It's already a foot long and once we add the camera it will grow even more. For now we will live with a inefficient design and refine it as we learn.
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Re: parachute deployment just an idea

Post by Spaceman Spiff » Fri Oct 31, 2008 4:41 pm

Looks great Tim!

I like your methodical testing approach. I hope you get permission to throw stuff off that parking garage first though. Years ago I got in trouble for throwing paper airplanes off our town library balcony. They had the cops come and my parents were called. I was grounded for weeks. Lucky for me I was a minor and didn't get arrested or anything.


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Re: parachute deployment just an idea

Post by U.S. Water Rockets1 » Sat Nov 01, 2008 10:10 pm

Tim Chen wrote:Here is the prototype MAD servo controller. It is designed to fin in a rocket as small as a T8 FTC. We have mounted it into a bottle cap so that can be slid in and out of a piece of T8 tube. T8 inside diameter is the same as the caps so they are used to hold the parts in place. The servo is mounted to another cap and uses a pushrod made from a large tie-wrap to eject the nose-cone.

We are preparing for drop-testing a crash test "dummy" rocket to see the best way to extract the parachute from the tight FTC. The rocket is just a weighted tube with fins and no electronics. We want to perfect the deploy without risking the electronics.

We have a few options:

1) Connect nose to the rocket with a streamer to create drag to pull the chute out from inside the nosecone.

2) Make a "clamshell" nosecone that is hinged and springs open when it is removed from the FTC and has the parachute stored inside. If there is not enough room in the nose for a parachute we will extend the nose with a section of T8 tube that will become the "clamshell".

3) The nose extends down one side of the rocket with a "door" that covers a parachute side-deploy bay with a spring loaded chute ejector. If we go this route we will possibly just glue the nose on and use the servo to unlatch a spring loaded parachute door.

Our perfect design would have the chute inside the nosecone 100% because we think that extra length is wasted space and weight and it also throws off the rocket stability. The more space efficient the deploy module is the better. It's already a foot long and once we add the camera it will grow even more. For now we will live with a inefficient design and refine it as we learn.
Hello Tim!

Your work is progressing very well! It's great to see you guys putting together an advanced FTC rocket. You guys, Reno1, TDF Water Rockets, Soren, RaZias, and many others on this forum are really making HUGE advances in Water Rockets. It's been amazing to see how much you guys have contributed in such a short time. Judging from the amount of email inquiries we get on our website it looks like interest in Water Rockets is growing by leaps and bounds. It's great to be able to refer them here for your great inspiration. Keep up the good work!

When we first got started in water rockets there was nothing but bickering, big talk, and one-upmanship from a groups of "bench-racers". It's good to see so many people building and flying instead of boasting and bloviating.


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