Rocket parachute ejection

[Greg O'Bryant]

Does anybody have a system that they really like for ejecting parachutes? I know that you can make a type of propellant fuse to time the ejection, but I was wondering if anybody has come up with a more reliable and altitude sensitive ejection device. I want to keep the engine as simple as possible so I would like to aviod using the propellant as the timer. Any thoughts would be helpful ecspecially if it is something that has really worked well for you. Thanks.

P.S. I made a batch of catalyzed sucrose propellant to get an idea of how fast it burns and to do some exdperiments. Lets just say that things are looking really good for making an end burner:)

[El-Kablooey]

how about something like a mercury switch and a small battery for a trigger? Maybe it could be set up so that when the rocket reaches it's apex and tilts the ejection charge would be ignited.

[Greg O'Bryant]

Thanks for all of the input. On Nakka's site he says that the mercury switch doesn't work. As soon as it goes to microgravity it sets the charge off. If I am going to set the time for N seconds after ignition I could use N length of canon fuse that is ignited from the motor flame to set off the charge, but this isn't that much different than using the propellant. The only advantage would be you would have less of a possibility of something going wrong in the engine itself, for example breaching the chamber at the delay grain junction. I was actually thinking of using an airspeed switch with back up elements as on Nakka's site. It is so much more elegant to have the rocket eject the parachute at the right time not the pre-set time.

[NickC]

i like the accelerometer way best. How do you wire all that? And what all would you need?

[Ray]

Greg and Richard Nakka are right, the mercury switch will trigger when the motor burns out. Not a good solution.

A photo transister will pby detect the flame of the motor as the sky during boost and deploy the recovery system.

The simplest solution would be to buy a timer from Perfect flite. They can be triggered on a G switch or a break wire. You can just FIRMLY tape them to the shock cord with a stick to keep them vertical for g switch use, or build a small avionics bay that will do the same.

Of course, there are many different types of Altimeters you can use. Perfect flite is my favorite, but GWhiz, AltAcc and others are available too. Some use barometric systems, others use accelerometers, one uses the magnetic field lines of the earth and several use both barometric and accelerometer based deployment. A good source of info is here.

Naturally, if you are concerned with CATO's, you'll want to use some thing that is cheap too.

Remember, there are only two kinds of experimental rocket motors, those that HAVE CATO'd, and those that are going too.

I've seen "N" class CATO's that completely destroyed rockets...airframe, recovery system, electronics etc. One of the motors continued up for around 1000ft AFTER it went through the rocket...

[Zippiot]

Anyone tried the airspeed sensors with the little flap stickin out the side of the rocket?

[larry cottrill]

Greg and Richard Nakka are right, the mercury switch will trigger when the motor burns out. Not a good solution.

Then that sounds to me like the perfect triggering event for a reasonable time delay. The mercury switch sets off a monostable (like a simple 555 timer circuit) which then activates the chute after a second or two (or however much you set up). Note that CMOS versions of the 555 are available, so the battery needed to run it could be VERY small/lightweight.

L Cottrill

[Ray]

Could be a solution to begin a timing event. I think it could work well for that.

You could do the 555 timer as you suggested, but the battery would need to be at least a 9V or something that will deliver a couple of amps of current for a second or two. Most e-matches, christmas tree bulbs, flash bulbs etc, need a pretty good amount of current to fire the charge. I won't use a battery that checks with a current less than 3 amps. I use ematches and christmas tree bulbs for my ejection charges.

I like the timers that Perfect flight makes...easy to program and tough. They've done all the hard work for you, the micro timer is only $25, and the mini timer is $35...not bad when you consider the investment you have in your rocket...

If you do a 555 timer for yourself, remember to allow for changing delay times, every rocket, every motor will want a different one. You'll need to provide a high current switch, relay, mosfet, etc for the firing channel.

I swear by an altimeter though, they allow you to dual deploy a rocket. This cuts down on the drift on recovery by allowing for a small chute to deploy at apogee, then another larger chute at a pre-determined altitude...saves a lot of walking, and lost rockets. When you start to do your own motor, the cost between a small motor, and a large motor is insignificant...so why not use the big one? Its always fun to know how high you pushed the rocket. Some of the altimeters out there will even allow you to develop a thrust curve for the motor.

[El-Kablooey]

I think you could get away with a few small watch-sized lithium batteries. I have used christmas bulbs for fireworks, and a 9-volt will stet off at least 100 before it loses its charge.

[Zippiot]

If the rocket is a decent size you an use the AA battery and board from a disposable camera. All you have to do is bridge the switch for the flash and replace with the micro timer, it sounds easy but it really isnt. The system should run somewhere around 330 volts but I donnot know the amps...

[Ray]

It seems that on this forum there is a stong push to "do it yourself", I like that, but I tend to focus on certain aspects of the hobby to do it myself.

I am an Electrical Engineer, and could certainly design, and test my own altimeters and timers, but I choose not too. I do that kind of work all day, and I need an escape from the day to day. Additional, I have found that others have done the work, and done the work well. I find myself asking, Why re-do what they have done? When it comes to electronics in a rocket, I tend to answer, I don't need to re-do it, I'll just use theirs. The cost is low, the companies have good reputations among the rocketry community, so really, why bother?

I want to focus my energies on the things that really captivate me. Designing, analysing and making rocket motors out of AP/HTPB. So far I have been reasonably successful, and the analysis part of the effort has been a real kick!

I guess, for everyone there is that thing that motivates them. I find that the commercial electronics part of rocketry is so well done that I don't find it interesting to come up with my own. I only have so much time in a day, and spending hours designing, assembling and testing a timer for deployment seems to be wasted effort, when I can buy one for $25 plus shipping.

To each their own :D

[Zippiot]

For 25 bux something reusable and small seems unbeatable, what kind of power does it need to be wired with to fire off an ejection charge?

[Ray]

Look here.

If that doesn't cover it fully, try re-reading the thread...all the info you are requesting is there...

[Ves]

Hello,

A 2weeks ago i make thist simple, cheap and lightweight parachute ejection system. Successfully tested on the groung. Flight test will be soon.

[NickC]

just get one of the G-Wiz LCX flight computers. $80 for basic model and $140 for the deluxe model with barometic altitude and a few other features, but the $80 will eject parachute at the apogee and will give you a calculated altitude. Also has other pyro outputs for things like multi-stage rockets. google G-Wiz flight computers