Building your own rockets

Rocket . . Altimeter . . Launcher
Building your own rocket can be as simple as duct taping some plastic fins to a cola bottle to as complicated as a multi-stage, electronically controlled recovery, carbon fiber reinforced rocket.  I have put a few things into words that could be helpful for someone wanting to build themselves a water rocket.
Most any soda bottle will work.  Pop bottles made of PETE plastic are designed to hold the pressure of the CO2 fizz to +100psi.  Bottled water containers generally are not.  Do not use these, they can explode.  Well, I guess anything will explode with enough pressure behind it... he he he

Anyway, 20 oz bottles are more aerodynamic than a 2 liter bottle, but they do not hold as much air.  The new 24 oz bottle are nice because they are the same diameter as the 20 oz but are longer.  The more volume you have the more oomph you will have behind your rocket. This said, if you can join the bottles together, you may attain a higher altitude.
In order to join 2 bottles together I use this method of gluing and using "lamp rod". 
Another joining method is to spice bottles together like Bruce Berggen does.  Note: I don't use his instructions for Converting Florescent Tube Covers into Rockets, I have some instructions on my web page here.

Your goal for fin materials: strong, waterproof, light, and aerodynamic.
That said, you can use corrugated plastic boxes, old broken CDs, credit/gift cards, balsa wood, styrofoam... the list goes on and on.
I personally have been using laminating plastic.  I take the thickest laminating sheet and send it through the laminator without anything inside it.  Then I take it out and put it inside of another sheet and run it through again.  I end up with 4 layers of clear laminated plastic. I then cut them to the shape I want and heat up the end I want to glue to the rocket. when it gets hot enough, I bend 1/4" of an inch over at a 90 degree angle.  This gives me plenty of surface area to glue it to the rocket.

Joining the fins to the rocket:
Duct tape is the quickest and easiest thing to use, but it sure is ugly.
PL Premium Construction Adhesive is what I use.  Unfortunately it takes a while to set up. You have to wait over night to use your rocket.  The good thing is that it is semi flexible after it sets up.  This is good because PETE bottles flex a lot.  You should use some sandpaper to ruff up the area that you will be applying glue to, so that it has something to stick to because plastics are generally smooth and slick.
Fin skirts:  Cut the top and bottom off of another bottle, then tape or glue this to the nozzle end of your rocket.  Glue your fins to this "skirt" so that when your rocket gets damaged, you can take off the fin skirt off and put it onto your next rocket quickly and easily.

Recovery:  Lawn darts or parachutes, that is the question.
Lawndart: If you make a rocket with no parachute, try duct taping a tennis ball the the nose.  This will make your rocket last a lot longer.

Inertia cap over parachute:
A nosecone with a weight in it.  It works on the principal of inertia.  At apogee the heavier nosecone wants to remain in motion while the rocket slows due to air resistance.  This makes it separate and the parachute comes out of the nosecone.  These work OK unless you launch at an angle or it is windy and your rocket "weather vanes" into the wind at apogee.  If this happens, the nosecone stays on and your rocket becomes a lawndart.

Air-speed Flap: 
I personally have not used one of these so I have no advice for you.  But basically it is a spring loaded flap that is held down by the air rushing past.  When the rocket slows down and reaches apogee, the spring pulls the flap up and releases the parachute.

There are different ways to use electronics to deploy a parachute.  Timers, light sensors, radio controlled, accelerometers, and pressure sensors are some of the ways I have read about that you can use electronic deployment. 
also see My Altimeter

Tomy Timer: named after the Tomy toy company 
The insides of a wind up toy can by used to make a timer to deploy a parachute. Here is a video of one in use. You gut the wind up toy for it's mechanism.  Find something you can jam the gears with to keep it from running until you pull the jammer out. (I use the end of a cable tie.) Tie the jammer to a string and tie the other end to your launcher so that when it launches, it pulls the jammer out and starts winding down.  Drill a small hole through the winder knob. Make a "pull pin" to put through that hole and tie a string to it. (I used a paper clip for the pin)  Tie a piece of elastic cord to the pull pin string.  Tie the elastic to your rocket so that when you pull on the pin it stretches the elastic before you put the pin in the wind knob. The string should block the parachute from coming out until the pin pulls away from the knob.  You need to glue the mechanism to your rocket.  Make sure you don't get any glue on your gears. 

My design is a tube that sits on top of the rocket.  I put the tomy timer on the inside.  I cut a few holes to access the jamming hole and to stick the winding knob through.  I cut an oval out for the parachute compartment and I tape in a section of plastic bag to make a pocket for the parachute to sit in.  I also make a door to close over the chute and tape it on at the bottom to make a hinge.

Two Stage:
You can make a two stage rocket using a staging device that operates off pressure from your rocket.  It is relatively easy to make.  Bruce Berggren has a description on how to make one. 
Using a nozzle can dramatically change the way your rocket performs.  I have used some "tee" nozzles on my FTC rockets.  A tee nozzle is one that sits inside of the rocket on top of the launch tube.  When the rocket comes off the launcher the nozzle is forced to the bottom of the bottle and it tries to exit the neck of the bottle.  Only you have an o-ring to stop it from coming all the way out.  The remaining water has to come out of the hole in the nozzle. This makes the acceleration phase longer.  The size of the hole controls how your rocket accelerates. 
The one pictured is made out of 1/2 PVC pipe, a 1/2 PVC pipe coupler, an O-ring, and a piece of plastic that I turned down on a lathe.  The 1/2 pipe has a deep grove in in for a thick O-ring to sit in. I glued a pipe coupler close to the O-ring but then cut it down to let the O-ring fit tighter against the pop bottle top.  The hardest thing to make was the plastic nozzle.  I made this one a bit elaborate, but all I really needed was to get something to block off the pipe and then drill a hole through the end.


Bernard Willaert is where I found electromagnetic deployment for the chute

  I used Bruce Berggren's launcher design (dead link)

Tim Sumrall has some good ideas (dead link)



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