Friday, December 01, 2006

Using the Potato Gun and Launching Rockets: A Few Tips

When you have thirty kids running around begging for pudding, sometimes it can be hard to give them all good instructions. These are a few tips that will help us get the most out of our meetings.
The Potato Gun
Nobody Likes a Misfire
Today at our fourth club meeting we did a ton of potato gun firing. We did have quite a few misfires, though - that is, times when the potato gun just didn't fire. There were also a few misses, although our aim was fairly good. In any case, here are a few tips for being a potato gun expert.

AIMING: If you want...
  • Maximum Distance: Hold the potato gun at a 45-degree angle.
  • Maximum Height: Hold the potato gun straight up, of course! :)
  • To Hit Something: If you're relatively close - say, half the width of the Lower Field - you should pretty much aim straight at the target. Aim a little bit up, but probably not more than 10 or (at most, if you're, say, all the way accross the Lower Field) 15 degrees. This one will just take practice.
POWER: How do I get the most?

  • We haven't yet done a lot of testing, but there's a perfect amount of hair spray to spray. We've found that 4 seconds works quite well.
  • Also, choose a nice big potato - bigger than the barrel. Use the sharpened edge of the barrel to cut it down to size. Try to avoid ANY air gaps on any side of the potato.

MISFIRES: Why do they happen, and how do you prevent it?

  • The potato gun will not fire if you have too little or too much hair spray in the chamber.
  • NOTE: More hair spray does NOT always mean it'll go farther! There's an optimal ration of air to fuel. If there's too much fuel and not enough air in the chamber, it won't ignite.
  • SO: don't spray too much! (That's a lot more common than spraying too little.) It it won't fire, wait! Air out the chamber.
  • Note that sometimes, misfires are out of your control. Sometimes a wire is loose or unplugged or broken or something like that. But 98% of misfires are thanks to having a bad air-to-fuel ratio.
DUDS: Why did the potato just softly plop out of the barrel?

  • Again, there is an optimal ratio of air to fuel. If you have just a little too much or too little hair spray, the potato may not go very far.
  • Also, the potato needs a good seal in the barrel. That is, it should fit very snugly, and give a good deal of resistance when you shove it down the barrel. Otherwise, all those explosive gasses can just escape out the gaps around the potato instead of launching the potato.
  • SO: spray for about four seconds. (It's probably worth experimenting a bit with the exact timing.) Don't have too long a countdown - three seconds will do it.

Push the button HARD

Rockets are, in some ways, a lot simpler to launch than is a potato gun to shoot. You don't need to optimize this or that. But it is a longer process. Here are the steps:

PREPARE THE ROCKET (note: I won't be too detailed about actually making the rocket.)

  • When your rocket body is all assembled, crumple up three or four pieces of fireproof wadding and stuff them down the body tube.
  • Attach the parachute, fold it up and put it into the body tube.
  • Take the bottom of the rocket off and put in the engine. Put the bottom back on.
  • Stick the black end of an igniter (the little metal wires split like a weird V) into the hole in the bottom of the engine. Secure it with one of those little plastic plugs - the things that look like thumb tacks. Bend the wires out to either side.


  • If there's no wind, keep the launch rod aiming straight up. If there's wind, tilt it slightly into the wind.
  • Slide the rocket down the launch rod. Try to suspend it off the metal disc an inch or two, e.g. by wrapping the rod in tape at that point. (The tape part isn't necessary, but helps.)
  • To test it, take the the black box (electronic control box thingy) and clip the ends of the wires together. Put the key in the hole and press down hard. If the light lights up, you're good to go. Otherwise, you need new batteries.
  • Clip the wires from the control box to the two wires of the igniter on the bottom of the rocket. Keep the clips from touching any other metal.
  • Walk as far away as you can with the control box. If the launch pad is tilted in any direction, stand behind it. The wires will come unclipped very easily, so you may want to have someone hold on to the wires by the launch pad so that when you pull it taut, it'll tug on them and not the fragile connection to the rocket.


  • Start a countdown
  • Around 3, put the key in the hole and press down hard.
  • Right on one, or even an instant sooner, press down hard on the black square button and hold it. Hold it! It'll take a second for the engine to light.

And that's it! :) Now you're all potato gun/rocket launch experts.

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