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Compressed Air Rocket Sled

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RocketsNorth

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My daughter who's a Junior in High School brought home her physics ISU (Independent Study Unit) assignment a few weeks back to build a vechile that could transport an egg 3 meters (10 feet) through a 1 foot x 1 foot tunnel. While she's an honor role student, physics is her weakest subject, so she asked me to give her some ideas. So naturally I suggested a Rocket Vechile and we got down to design.
The 3 main considerations we needed to address were:
  1. She needed to be able to carry it the mile and a half to school easily
  2. It had to be "self powered"
  3. She had to do most of the work herself
After much debate, we decided that a "pressure cylinder" made from 4" PVC pipe fasted to a balsa wood sheet pumped up with a locking bicycle pump. My son chipped in the BAM wheels for his Element skateboard.

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RocketsNorth

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We grabbed a tire valve (valve stem removed) and drilled a hole in one of the end caps and glued the "pressure vessel" together.
The threads needed to be sanded down to allow the pump to release smoothly with 80 grit sandpaper

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RocketsNorth

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We drilled out a 5/16" hole through some 1"x1" I had left over from our fence repair last year and used a treaded rod for an axel.

Finally, we Duct Taped the presure vessel to the balsa wood base

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RocketsNorth

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Last night we gave it a try in the garage.

With about 35 or 40 lbs of air we launched the sled and it ran 12 feet in about 1.5 seconds or a shade over 5mph.
Over the weekend we'll tune the wheels and hopefully we can get the speed down about a second over the same distance.
 

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