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Converting gravitational potential energy into air pressure to launch a projectile? Answered

Hello my name is Aaron! I am a high school senior from northeastern Kentucky designing a pneumatic system of sorts for a science competition and need some help. I will be building a device that converts gravitational potential energy, from a falling mass, into air pressure (or possibly the movement of air depending on the design) to launch a projectile a specific distance (max distance needed is 8.25 m).

What I am thinking about doing is using one double action pneumatic cylinder (DAPC) as a bellow in which a falling mass (max 3.500 kg at a max 90 cm) would strike its piston shaft, creating positive pressure within the system. With that positive pressure another DAPC’s piston would simultaneously strike our projectile sending it airborne in theory. Below there is an illustration of my idea, sorry about the poor quality.

So what I need help determining is would this design work before I start buying parts? If so what approximate sizes should the two cylinders be and should they be different sizes to maximize the force exerted on the projectile? If you have any other ideas concerning the design or any questions about the project PLEASE feel free to share!!! Below are some of the design rules that pertain to this project along with some notes in italics about them. Thank you very much for your time in advance!


   -Prior to competition, teams will design, construct, and calibrate a single device capable of launching projectiles into a target and collect data regarding device parameters and performance.

Design Constraints:
   -The launching force must be entirely supplied by the gravitational potential energy from a falling mass less than or equal to 3.500 kg. Any device part whose potential energy decreases and provides launch energy is considered part of the mass. The mass may consist of multiple discrete parts, which together count as the total mass.

   -During each launch, the gravitational potential energy must be converted to air pressure or air movement, which is then used to launch the projectile, either directly (e.g., pop gun style, etc.) or indirectly (e.g., using a pneumatic cylinder to swing an arm, etc.)
All device air chambers must start at ambient air pressure and must automatically return to ambient air pressure.

   -The launching device (would look similar to this with the adjustable angle to accommodate different ranges), including the projectile and all components, must fit within a 75.0 cm x 75.0 cm x 1.00 m box in ready-to-launch configuration, in any orientation chosen by the team. Weights used to stabilize the device must be within the box.

   -The triggering device (would look something like this except elevated with a mass suspended ready to be released) in not considered part of the device and must not contribute energy to the launch. It must extend out of the launch area, allow for the competitors to remain at least 1.00 m away from the launch area, and does not need to return to the launch area after launch. The triggering device must not pose a danger to anyone due to flying parts or excessive movement outside the launch area.

   -Teams must provide unmodified tennis, racquet, ping pong, and/or plastic practice golf balls to be used as projectiles. Teams may change projectiles for each launch.

   -The launching device must be designed and operated in such a way to not damage or alter the floor.

   -Electrical components are not allowed as part of the device or triggering device.

The Competition:
   -Two targets, designated by small marks on tape on the floor or panels lying on the floor, must be placed in front of and centered on an imaginary line parallel to the launch direction that bisects the launch are. Supervisors are encouraged to place sand, cat litter, or similar substance in the area around the targets to help indicate landing spots.

   -The targets must be placed in front of the launch area at distances between 2.00 m and 8.00 m (in intervals of 10 cm). A distance of at least 2.00 m must separate the targets. Target distances must not be announced until after impound is over and must be the same for all teams. Room ceiling height should be considered when setting the distances.



3 years ago

Looks nice, I would suggest putting the projectile at the last centimeter or two so it strikes the projectile rather than pushing it, this should give you a bit more speed and range.

Please post pictures if it works out, it looks like a nice design!

Thank you very much and I will make sure to!

Post photos if it works out, it would be cool to see!

Keep it simple: drop a weight on a plastic bottle.

That is what the trail event suggested to use last year, which worked well enough. I am just concerned with the constancy of a plastic bottle over repeated strikes from a 8 lbs. weight.

Use several bottles from the same brand, and switch them out if they look battered.


3 years ago

Keep in mind that as you compress air it gets hot. Hot enough to ignite materials if the compression is great enough. Anything that you use that is plastic might melt.

You need to hold back the air and allow it to build up pressure before it enters the gun side. You will get the best launch if it reaches max pressure before release. One way to accomplish this is a delayed release on the gun. A more automatic way would be to use some kind of burst membrane. The membrane would remain intact until it reaches a certain pressure and then it would burst letting all the air go at once.

That is an excellent idea but due to safety reasons we are not allowed to have "stored" pressure any duration of time, which stinks.

Can you use water and air, or are you restricted to just air ?