# Thread: Vacuum cannon trial and error...Success!!!

1. Originally Posted by kls-ccc
What if you used a larger pipe on the vacuum end, reduced it on the other end to hold the ping pong ball, so you would have more air rushing in?
To much air would get past the ping pong ball, so it wouldn't move fast enough.
The pipe needs to be enough bigger than the ball that a little air will get past it, but not so much bigger that to much of the air goes around it.

Visualize it as blowing a ping pong ball down a pipe with 14.7 psi of air pressure.
The ping pong ball will go much faster down a pipe that has an inner diameter just slightly larger than the ball than it will down a larger pipe.

2. The thought was if you have a larger volume of air coming in the other end, when it gets to the other end which is smaller and has the ball in it, you'll have a larger volume of air trying to go down that smaller tube which should increase the pressure putting more force behind the ball.

3. Originally Posted by kls-ccc
The thought was if you have a larger volume of air coming in the other end, when it gets to the other end which is smaller and has the ball in it, you'll have a larger volume of air trying to go down that smaller tube which should increase the pressure putting more force behind the ball.
Remember that the end the ball is supposed to shoot out of is still closed with tape, if to much air has gotten past the ball before it gets to the end, and the ball is not moving fast enough as it approaches the closed end of the pipe , the the small burst of high pressure re-compressed air needed to break the tape won't happen.
The tape isn't broken by the ball physically contacting it.

If you want to REALLY make the ball go fast, have something more than atmospheric pressure driving air in through the end the end where the tape gets cut.
Imagine shooting a ping pong ball at a high enough velocity that it punches straight through a ping pong paddle.

4. Watch this video. Amazing what a ping pong ball can do at super sonic speeds! Someone posted this in one of these forums. I thought it was cool, so I tried it. Sub-sonic in my case. I'm waiting for Marks sound barrier breaker!
http://www.youtube.com/watch?v=YYNCGZCul1Q

5. Your limited to 14psi... but on the positive side, the pressure remains almost constant, where as with a typical cannon using a explosive propellant, the pressure peaks, then drops off as the gasses expand inside the barrel.

6. Originally Posted by mark beiser
I'm going to try my hand at building a super sonic one.
Haven't seen your obituary yet. Must mean you haven't built it yet?

7. Originally Posted by doc havoc
Haven't seen your obituary yet. Must mean you haven't built it yet?
Been busy with work and my yard. Had a record February and March, and the yard is a total redo down to bare earth and back.

The super sonic vacuum cannon is still on the agenda though.
Hmm, I am taking a few vacation days this week to relax, and it should rain a bit, so won't be able to work on the yard anyway...

8. Saw your yard work in another thread. Figured that was keeping you busy. Still got at least a foot of snow in my yard. Wish I could start some yard work.

9. Well, I built my cannon today, still a bit of refinement needed though.

The basic vacuum only setup.

10. The first shot with a pressure chamber on it.

11. Ping Pong ball vs. Ping Pong paddle.

I don't think I'm quite up to super sonic speed, but it is pretty close.
I need to work on a nozzle for the air inlet to get the velocity up more, and make a more secure target platform than the wet cardboard box that happened to be on my back patio.

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