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Topic: 2 Stage Model Rocket feasibility (Read 4 times) previous topic - next topic

radman

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I don't imagine any well-built Arduino would be troubled by the sort of accelerations likely to be encountered by amateur rockets, assuming all connections are soldered.

saulton7 seems to know what he is about but he also has budget considerations. My rocket attempts were all pretty terminal affairs, with people suggesting home made gunpowder I guess they have had similar experiences.  ]:)
I would be concerned not so much about about the board itself but how it was mounted, whether or not it would short and if/how it was protected from engine failure.

kg4wsv

Arduinos fly in rockets just fine.  Yesterday I sent my 4" 10lb Patriot up to 2500' on a J440. It was a bit windy, so I used a smaller motor than I'd originally planned. In the nose was a serial arduino with a radioshield connected to a Garmin GPS18 and a ham radio for tracking.  That particular rig not only survived that, but several previous flights to higher altitudes (5000+ ft), including one where the main failed to deploy and it hit the ground (salt, actually, at the Bonneville salt flats) at 50+MPH.  That impact bent some pins on the shield because the bulkhead broke loose and tried to go out the side of the nosecone, but it was otherwise undamaged.

Relays are not a good idea in a rocket, as G forces and vibrations beyond a typical relay's ratings may be encountered.  Use something solid state, such as a FET like grumpy_mike described.

If the circuit will be anywhere that it can cause the flight to fail unsafely (e.g. fail to deploy a chute because the second stage motor didn't ignite), don't do it.

A pair of CR123A batteries are smaller and provide much more current than four AAs, while providing the same voltage.

If you change igniters, make sure they're compatible with your motor.

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but I'd have expected the second stage to be triggered by the first stage separating, and I'd expect that to be triggered somehow by the expiry of the first stage.


That's how it happens on model (e.g. Estes sized) rockets.  A special first stage motor burns through the top and lights the next stage.

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Doing it based on a timer somehow doesn't feel like a good way to synchronise the handover to the next stage.


Works for NASA - that's how they stage their multi-stage sounding rockets (and deploy payloads, parachutes, etc).  High power rocketry also uses timers for staging.  As a matter of fact, I just bought a couple of commercial units.  Haven't even used one yet, and I'm already planning to make my own, probably arduino-compatible. :)

-j

terryking228

Hi,
Many people use Arduino Pro Mini (which can fit inside a ping-pong ball) for balloon and rocket work;

http://arduino-direct.com/sunshop/index.php?l=product_detail&p=107

Estes ignitors, "electric matches" and EB Caps  (Electric Blasting Caps) are made with low-resistance high-current ignitor wires for safety.  In this case, with care, the Flashlight Bulb Filament igniter may (with great care) be suitable.  It is the favorite of the CellPhoneTerrorist group... Sigh... 

Google is your friend; see what others are doing...


DISCLAIMER: Mentioned stuff from my own shop...

Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

saulton7

I planned on putting the Arduino and other circuits in the nose cone of the rocket, also i have solved the low current ignitor issue, as i found these http://www.amainhobbies.com/product_info.php/cPath/1683_1686/products_id/59816/n/Quest-Q2G2-Rocket-Motor-Igniter-Pack-6?utm_source=Google-Base&utm_medium=cpc&utm_campaign=Product-Feeds&source=google_ext

they should be able to be fired by a couple of digital pins wired together (about 4 i think)

zoomkat

If it were my time and money, I 'd look at what others are using for similar size/design rockets. Unless the rocket is of unusually large size, I can't see the improvement over a very small and simple piece of timed fuse.
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

kduin

You could also use an Attiny85-Chip (about 3$) instead of a whole Arduino-Board.
It's enough hardware for simple in/out operations. (i just built a device with a pusbutton, led, reed-relays and pir-sensor with the attiny, i'm also a arduino newbie)
See this tutorial: http://hlt.media.mit.edu/?p=1229

kg4wsv

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I can't see the improvement over a very small and simple piece of timed fuse.


Really?

What about safety?

You can not push a fire button, but once you light a fuse, you can't un-light it if an unsafe situation develops (someone wanders into the LZ, the dog knocks over the launch pad, etc).

Most 2nd stage ignition systems are inside the rocket, between the first and second stages.  It's not particularly practical to assemble stages with a burning fuse inside.  The timing would be tough, too.



The quest igniters can not be reliably fired directly from digital outputs.  Use a digital out to switch a transistor that fires the igniter.

-j

zoomkat

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You can not push a fire button, but once you light a fuse, you can't un-light it if an unsafe situation develops (someone wanders into the LZ, the dog knocks over the launch pad, etc).


Ok, backyard project.  :) I thought the discussion was about second stage ignition, not initial launch. So what are you going to do when this thing rolls over from being top heavy and zips around the LZ?

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Most 2nd stage ignition systems are inside the rocket, between the first and second stages.  It's not particularly practical to assemble stages with a burning fuse inside.  The timing would be tough, too.


Yes don't light the second stage fuse while you are assembling the rocket. See, you are slowly getting there!
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

GoForSmoke

The smart thing is the way that Estes engines do work. They don't ignite the next stage until after the first stage has burned. Still, I have seen some 2nd stages light at lower flight path angle than was planned.

I knew a EE student who talked about delayed fuse lighters (for M-80) that used a capacitor and resistor to hold a transistor closed and another larger capacitor to ignite the fuse when the smaller one ran down. You can be accurate since you can test the 'fuse' ahead of time and you can feed the smaller cap right up to the moment of launch.

Easy igniter. Run 2 wires into some steel wool with a little fine powder mixed in. Steel wool burns hot. I used to prefer flash powder but since 9-11 things aren't so easy or fun any more. :-(
OTOH wet your powder and coat a very thin wire with the mud and let it dry then overload that wire.
I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.

saulton7


You need what is known as a logic level n-channel FET, connect the source to ground, the gate through a  100 ohm resistor to the arduino output pin and the drain to your load. Connect the other end of the load to the positive of your power supply and connect the negative of the supply to ground. As simple as that.


Where could i get such a FET? i usually buy my stuff from sparkfun. Could i substitute the FET with another type of transistor? (in the event sparkfun does not carry an FET)

also, how bad is a rocket being top heavy?

GoForSmoke

http://www.youtube.com/watch?v=7eT-buIKUpY

9V is overkill.
I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.

terryking228

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also, how bad is a rocket being top heavy?


See: http://nar.org/NARTS/TR13.html  "Rocket Stability"   

Center of pressure needs to be a ways behind center of gravity.

Therefore fins.
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

kg4wsv

A little top heavy is actually better than tail heavy.  If the center of pressure (CP) is ahead of the center of gravity (CG), the rocket is unstable and won't fly straight (think fireworks rocket when the stick falls off and it goes in crazy gyrations on or just above the ground).

Ideally the CG will be one "caliber" (body diameter) forward of the CP.

If the CG is too far forward (i.e. very top heavy), the rocket wil be overstable, and be very prone to turning into the wind.

If the rocket is too heavy it may not be moving fast enough when it leaves the rod/rail, and as a result fly horizontally.

You can download OpenRocket and use it to create a model of your rocket and simulate how it will fly.

-j

saulton7

Can Open Rocket simulate two stage rockets?

kg4wsv

Yes, although I'm not crazy about the data display.  It seems to forget about the first stage and only track the second.

-j

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