Air Trajectory: Converting gravitational potential energy into air pressure to launch a projectile

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1. Sep 30, 2014

ahoback

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!
• Description:
• 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 http://gallery.scioly.org/albums/2/normal_a2j_DSC_0004.jpg [Broken], 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.

Last edited by a moderator: May 7, 2017
2. Oct 6, 2014

Greg Bernhardt

Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

3. Oct 8, 2014

ahoback

Yes I can. What I am really needing help with is determining the proper dimensions of the pistons. Should the bellow piston have a greater working volume than the striking piston? Should the bellow piston have a greater bore diameter than the striking piston? I am just trying to achieve the best transfer of energy from the falling mass, through a pneumatic system, to projectile. Thank you for your time!

4. Oct 10, 2014

CWatters

Do they have to be separate devices connected by a small bore pipe? How about two pistons in one pipe - perhaps with a large bore flexible coupling pipe between them to reduce losses? Do you even need a piston in the launching side or could the projectile be the piston? Just some ideas to play with.

5. Oct 12, 2014

ahoback

Thank you for the response! I was actually planning on using a large bore flexible coupling pipe between the two pistons. When you say could the projectile "be the piston" are you thinking about loading the projectile into a tube (somewhat like a potato gun) and having the pressure created from the bellow piston launch it?

6. Oct 13, 2014

CWatters

Yes. Why accelerate (put energy into) the mass of a perhaps unnecessary piston.

7. Jan 1, 2015

Lucas B

Hi my name is Lucas and I'm from Missouri and I'm in a similar event. I've been having trouble getting mine to launch the projectile far enough and I was wondering if you have had any luck with getting yours to work.

8. Jan 3, 2015

CWatters

Hi Lucas,

It would be interesting to calculate the efficiency of the launcher. Calculate the available energy (the PE in the falling weight) and the energy in the projectile (idealy measure the launch velocity but you could calculate it from the range achieved and use KE=0.5mv^2). The ratio would give you the efficiency of the conversion.

9. Jan 3, 2015

Lucas B

Thanks for the input but I got it figured out after more looking.

10. Feb 11, 2015

Brendon

Hey, i'm doing a similar Air trajectory layout, I was wondering how did your setup go ahoback? Did the two pistons work better then using one piston connecting to a PVC pipe tube to launch the ball? After making the layout and competing did you find anything you wish you had changed or modified?