Building a simple but unusual rocket

I’m going to show you how to turn an ordinary badminton birdie into a real launchable rocket. These are easy to make and bigtime fun to fly, plus they don't go so high that you'll lose it.

Best of all, they fly on Estes "mini" motors. You can find these in the toy department at WalMart, and a pack of four will cost around five bucks. You're going to need one to help you construct the rocket, so pick up a pack before you start. Look for motors labeled A10-3T or A3-4T, they'll be a little less than 3" long and about one half inch in diameter (pinky sized).

If you need more information about rocketry, check out my Rocketry archives, there's lots there, plus links to even more.

I'm going to assume that you have a launch pad and controller. The ones that come with Estes or Quest starter kits work fine. Starter sets are cheap, include everything you need and the value is very good.

And finally, just to prove I'm not a complete loon, here's the original plans for the birdie rocket as it originally appeared as an Estes rocket kit.

(in the extended entry)

Click on the pictures for Saturn V size.

Tools
Scissors
X-acto knife or razor blade
Pencil
Circle template – I used an empty spice jar

Materials
Badminton Birdie (aka shuttlecock)
Thin cardboard (from a cereal box or soda 12-pack is perfect)
Cardboard tube (Estes BT-5, or make your own)
Soda straw
Yellow or white glue
Hot melt glue

Instructions

Motor Mount Tube
The only real complicated step is right up front, and that's only if you have to make your own motor mount tube. I'll explain how, and then suggest a couple of super easy alternatives.

Cut a strip of thin cardboard (manilla file folder is ideal) 2.75" wide and about 4 or 5 inches long. Pre-curl it by running it over the edge of a table. Wrap it around one of the mini-motors, it should wrap two or three times. On the last wrap, squirt a little glue under the layer and use the rubber bands to hold things together while the glue dries. Be careful not to glue the motor inside the tube permanently, it has to be able to slide out. What you'll wind up with is a cardboard tube 2.75" long. Let it dry.

That's the hard way (and it's not all that hard to do). There are some easier ways to do it though. First off, you can buy that size tube from hobby shops and cut it to length, but a package contains 3 18" lengths, which is seriously oversupply for what you need (unless you're making a lot of these). If you go this route, look for Estes BT-5.

You can also buy a rocket kit and salvage the parts from it. Current Estes kits that use BT-5's are the Mosquito, Quark, and Swift. There are probably others, look for a rocket kit that uses the mini-motors (A10-3T, A3-4T, etc. - look for the "T" at the end of the motor designation).

Centering Ring

Using a template (I used a small empty jar), mark a circle on the cardboard. See the picture farther down to judge about how big a circle you need. Take your motor mount tube and use it to mark another circle centered inside the first.

Carefully cut out the inner circle with the X-acto knife, and then cut out the outer circle using scissors or the knife. Be careful, that knife is sharp! Take your time and make multiple light passes instead of trying to cut through the cardboard in one stroke.

Save that inner circle. We're going to use it in a moment.

Assemble the motor mount
Glue that inner circle into the very top of the motor mount. This makes a bulkhead that protects the birdie from the ejection charge of the motor.

When that has dried a bit, fit the centering ring into the bottom of the birdie and then slide the motor tube into place until the top end (with the bulkhead) touches the front of the birdie. Glue the motor tube to the centering ring with a bead of glue where they meet. Remove the centering ring from the birdie and do both sides of the centering ring/motor tube joint. Let it dry.

Aligning the launch lug
Next you need to place a hole in the centering ring that the launch rod will go through when it's on the pad. Line it up by using the rod and either punch the hole with a hole punch or drill it with the x-acto blade. If it looks like the rod won't pass through the cardboard and birdie smoothly (important!), take a short length of soda straw and glue it into place as a conduit for the rod to pass through.

Gluing it together
Run a bead of hot melt glue around the perimeter of the cardboard ring where it meets the birdie to join the two pieces together. That's it!

Launch Instructions
Put a motor into the motor tube and insert the igniter normally. Slide the rocket onto the pad by passing the launch rod through the straw or holes you made for that. Hook up the igniter to the controller wires, count down and launch.

When the ejection charge goes off, it will eject the motor out the back of the tube, which lightens the birdie enough to recover safely via drag or "featherweight" recovery.

To fly it again, just insert another motor and you're good to go.

Why it works
A badminton birdie stays stable because the rubber nose is heavily weighted compared to the rest of the body and the many holes (feathers) create enormous amounts of drag. These two factors combines keep the birdie flying nose first, but it also decelerates quickly when the thrust ends (either by striking with the racquet or by our rocket engine).

On recovery, the extreme amount of surface area compared to the light weight combine to keep the speeds low. It's the same principle as a whiffle ball, no matter how hard you throw it, the area/mass ratio means it'll slow almost instantly.

Posted by Ted at April 3, 2005 10:31 AM | TrackBack