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Ping-Pong Ball Helicopters

This describes how to make freon-powered helicopters out of ping pong balls. No fire, no explosives, but fun anyway.

This article is a little tough to build, but is fun to play around with! This is a long article, I just knew you wouldn’t skip this one!! You will be glad you didn’t! 🙂

You will need:

  • Ping Pong balls (1 for each helicopter to be made)
  • Thin round wooden sticks about 6 inches long. I use the industrial cotton swabs with the cotton ball broken off.
  • Strong glue. I suggest 2-part epoxy, but others may work. Don’t use a glue that dissolves the ping pong ball. Water based glues might work, I don’t know.
  • The smallest diameter tubing you can find. I use heat shrink tubing that has been heated so it has been totally shrunk as far as possible. Tubing from a can of WD-40 would also probably work, but it is tough to bend and the opening might be a bit small.
  • heat-shrink tubing of the smallest and next smallest sizes. This is used for filling the ball.
  • A straight pin and a lighter or match to melt tiny holes in the ball.
  • Cellophane tape to be used to make a lifting wing (optional)
  • Assorted hand tools you might like to use.
  • For the launching station, you will need:
  • A tube of about 1/4 to 1/2 inch in diameter. I suggest removing the ink from a Bic pen (dispose of the ink properly, it is toxic! 🙂
  • Several rubber bands.
  • A can of freon. This is sold as Freeze-Mist (for cooling parts) or as canned air (for blowing dust out of hard to reach places). Same stuff, but you will have to fill with the canned air can held upside down to get liquid to come out. You can get this stuff at electronics supply houses (I think radio shack might sell it) or the assembly area at work. Guess where I get mine?
  • Some old coffee cup, glass or beer mug. I use an old coffee mug that has some stupid advertising on it. At least now it has a purpose.

The basic idea is to place the wood stick up through the axis of the ball and have a tube on the axis of rotation sticking out the side. As you twirl the stick, the tube should spin like one spoke in a wheel. (see pictures) The tube has a right angle bend at the end. .

Diagram for Construction:

How to build Ping-Pong Ball Helicopters

Method:

To make this device, hold the pin with a pair of pliars and heat the end with the pin head with the lighter. Use this to melt a hole in the side of the ball just big enough to put the stick in. Put a small drop of glue (the smaller the better, you want to watch the weight) on the tip of the stick and insert it all the way in to the ball so that the glue sticks to the other side. Take care to get this stick as close as possible on the center line. Now put some more glue around the base of the stick where it enters the ball to seal it against pressure. Slide the stick in and out a bit so that there is also glue inside the penetration to help sealing. If you have patience, set the assembly aside until the glue hardens. It’s easier if the stick is glued permanently when you go on to the next step. Take this time to make several of these assemblies. By the time you finish the last, the first should be hard enough to work with if you used epoxy glue like I suggested. Be careful not to try and pull the stick out.

Now, heat the pin up again and melt a hole in the ball at the ‘equator’ (assuming the stick defines the ‘poles’) that is just big enough to allow you to insert the tubing. Glue this in so that it sticks straight out the side. I suggest using some type of plastic tube that you can easily form by heating and bending. Set the whole thing aside until it is good and hard. Take your time and let it harden over night.

Now, you get to form the exhaust port. Bend the tube so that it points in the plane of rotation. Just bend the very end, leaving about 1/4 to 1/2 inch after the bend. The tube should be a couple of inches long. Make a few different models with different length tubes to see what works best. Be careful not to crimp the tube when bending it. Angle the tube slightly (about 4 or 5 degrees, maybe more but not much more) toward the direction of the stick. This will impart a downward force during launch and cause the helicopter to fly in the direction defined by the axis of the stick, but toward the sealed end where the stick tip is glued to the inside of the ball.

If you want to, use the tape to make a small blade for the helicopter to give added lift. Don’t make it too wide. Attatch the tape so that it is between the ball and the bend in the tube. The tape is attached to the tube for stability. Experiment with different shapes and angles to get the best performance.

You now have a completed helicopter waiting to be used.

To make the launching station, use all the rubber bands to attatch the launching tube to the side of the coffee cup. Make sure they hold firmly and double-wrap the rubber bands if you have to. Be creative, but make it sturdy.

Now, you will need to make the filling station. Squirt some freon out of the can. You should see drops of liquid come shooting out. If you only get a blast of air, try holding the can upside-down while squirting. If you still get nothing, try a different can or a different brand. The drops that come out should be VERY cold, and evaporate as soon as the touch just about anything solid. If they don’t, it isn’t freon. Use only freon.

Use some of the heatshrink tubing to make a coupling from the tube that comes out of the can of freon (make sure it comes with a tube!) to the tube that comes out of the helicopter. Glue the end attached to the freon tube to the tube so it is gas-tite. Form the other end so it slides snuggly around the outside of the tube from the helicopter. This is the tricky part, since you want a good pressure seal but want to be able to remove it at the proper time.

Now, it’s time to launch!!!!!

When the boss is gone (if you are at work) to lunch or home, take your new toys out. Place the launch station (coffee cup and tube) on the floor so that the tube points straight up. Place the stick of the helicopter into the tube. If you can, make sure there is enough clearance so the stick goes all the way through the tube and the ball rests on the top of the tube, but there is still clearance between the end of the stick and the floor. The helicopter should now spin freely in the tube, with the exhaust tube going round and round.

To fill, stick the coupling on to the end of the exhaust nozzle and hold it tight with your fingers. It will try to slip off, but if you made it right it should fit tightly without too much problem. If it is too loose, aim a heat gun at it for a few seconds so it shrinks (make sure it is coupled to the helicopter when you do this) and let it cool for a bit. Now, hold the coupling in place and squirt the freon. The ball will fill with liquid freon, and frost or condensate will form around the outside of the ball. Stop spraying, but don’t remove the freon can yet. Press your hand slightly against the bottom of the ball for a moment to warm it up as much as possible. If you see gas or liquid leaking from either of your glue joints, fix it now. (make sure to empty the freon out of the ball or let it bubble off before applying glue and letting it harden). Once it is warm enough, let go of the ball and push the coupling off the exhaust tube of the helicopter. The freon will come shooting out, the ball will spin rapidly, and the helicopter will take off!! Yippee!!! Call all of your friends into the room and show them your new toy! Let them try it.

Cautions:

About the only dangers I can think of is if the boss catches you using up all his freon or wasting company time. Then again, if he is cool about things he might want to try it himself. This is the time to share and bond.

Freon boils at room temp and whatever it touches get very cold (about -50 F) so you can get frost burns from the stuff if you spray it right on your skin. It takes a fair amount to do this, and if you are careful you will have no problems.

Variations:

Try changing the angle of the bend in the exhaust tube to point down toward the stick more. This will give more lift, but decrease the spin rate. Spin is needed to keep the helicopter stable, so don’t bend it straight down.

Try changing the size, shape, and angle of attach for the blade (if you use one) to get more lift. This will also slow down the spin rate, so don’t do it too much. Remember that as the helicopter spins faster, the leading edge of the blade will tend to curve upward from the air pressure hitting it, giving you more lift.

Try putting a little water in the ball before filling it with freon. This is tough to do, but the best way I have found is to fill your mouth with water, put the exhaust tube in your mouth, suck a bit of air out of the ball, and let the vaccuum formed pull the water back into the ball. Don’t put too much water in or it will get heavy and not work. Spit out the remaining water in your mouth and don’t swallow it or take the air you sucked out all the way into your lungs, as it contains freon if you have used the helicopter at least once before. Water in the ball does two things, it provides a good source of heat to let the freon boil quickly when things get going, and it provides mass for the freon to push out the tube. The water will be pushed by centrifigal force up the sides of the ball and will exit through the tube, giving a better lift off and spraying water all over. This is kind of messy, so I suggest doing it outside only. Sometimes the water will get so cold it forms ice crystals. If you use too much water, you also run the risk of ice forming in the exhaust tube and sealing it off. Make sure the ball is at room temperature before putting water into it. If ice does form, hold the ball in your hand and roll the tube with your fingers to provide heat to melt the ice.

This toy will fly to about 30 or 40 feet straight up before the gas runs out, assuming you have things adjusted right. Sometimes it will spin but not leave the tube. This is caused by not enough downward angle on the exhaust tube (see variations above) or not warming the ball enough before lift off. It is important to have the freon as close as possible to room temp so it will boil more rapidly and come out faster.

I hope you have as much fun as I have with this Ping-Pong Ball Helicopter.


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