Vacuum cannon trial and error...Success!!!

[doc havoc]

The cannon fires at about 1:08. The bang scared me enough that you can see the camera jump quite a bit. I would say it is equivalent to a .22 caliber snub nose revolver report. This was an empty can. We had about a dozen failed attempts before we actually got it working.

[doc havoc]

There is no compressed gas used for this. It is strictly atmospheric pressure and a vacuum. With both ends of the pipe sealed with tape, a vacuum is pulled on the pipe. When the tape on one end is cut, atmospheric pressure pushes air into the pipe. Since the pipe was in a vacuum there is little to no air resistance to hinder the acceleration of the ping pong ball. As the air rushes in, some of it bypasses the ping pong ball and gets between the ball and the tape on the exit side of the barrel. With the ball moving up the barrel, this creates a piston in a cylinder effect and compresses the air in front of the ball, which blows the tape out and allows the ping pong ball to exit the barrel. I don't have any means of measuring the velocity of the ball, but I did read/watch a video posted on h-talk and the physics instructor (Purdue) estimated a muzzel velocity of nearly 600 feet per second. We have not fired for distance yet. That will be the next thing we try. I'm guessing that due to the non-aerodynamic design of the ball and it's lack of weight, it will not go very far.

[KickedGinger]

There is no compressed gas used for this. It is strictly atmospheric pressure and a vacuum. With both ends of the pipe sealed with tape, a vacuum is pulled on the pipe. When the tape on one end is cut, atmospheric pressure pushes air into the pipe. Since the pipe was in a vacuum there is little to no air resistance to hinder the acceleration of the ping pong ball. As the air rushes in, some of it bypasses the ping pong ball and gets between the ball and the tape on the exit side of the barrel. With the ball moving up the barrel, this creates a piston in a cylinder effect and compresses the air in front of the ball, which blows the tape out and allows the ping pong ball to exit the barrel. I don't have any means of measuring the velocity of the ball, but I did read/watch a video posted on h-talk and the physics instructor (Purdue) estimated a muzzel velocity of nearly 600 feet per second. We have not fired for distance yet. That will be the next thing we try. I'm guessing that due to the non-aerodynamic design of the ball and it's lack of weight, it will not go very far.

A golf ball fits perect inside of SRD-21
I wonder how well that would work.

[dandyme]

I'm glad you guys are being productive.

[mark beiser]

A golf ball fits perect inside of SRD-21
I wonder how well that would work.

Not very well, to heavy.

[doc havoc]

I'm glad you guys are being productive.

I can sense the sarcasm dripping off your comment. It was part lesson (vacuum and atmospheric pressure), part stress reliever and part fun. We didn't waste any class time on this. It was assembled and tested during breaks and outside of class. This cannon shoots subsonic. They (the students) want to build a supersonic cannon next. I don't think that will happen on my watch. I see way too many things going wrong.

[KickedGinger]

Not very well, to heavy.

Is this based on assumption or have you tried this?

[mark beiser]

Is this based on assumption or have you tried this?

It is based on being familiar with the how the vacuum cannon works.

The ball is carried down the pipe by the air rushing past it when the tape on the end where the ball is gets cut. The tape at the other end gets blown out by a burst of air that gets compressed when the ball nears the end of the pipe.
Anything that weighs more than a few grams won't be going very fast when it gets to the end of the pipe.
It may not even move down the pipe fast enough to cause the pressure wave needed to break the tape.

If the vacuum cannon was one designed to shoot a ping pong ball at super sonic speeds, it could shoot a golf ball at a pretty good clip, due to the compressed air driving it, but only at a small fraction of the velocity it could shoot a ping pong ball.

[ryan1088]

That is awesome!

[KickedGinger]

It is based on being familiar with the how the vacuum cannon works.

The ball is carried down the pipe by the air rushing past it when the tape on the end where the ball is gets cut. The tape at the other end gets blown out by a burst of air that gets compressed when the ball nears the end of the pipe.
Anything that weighs more than a few grams won't be going very fast when it gets to the end of the pipe.
It may not even move down the pipe fast enough to cause the pressure wave needed to break the tape.

If the vacuum cannon was one designed to shoot a ping pong ball at super sonic speeds, it could shoot a golf ball at a pretty good clip, due to the compressed air driving it, but only at a small fraction of the velocity it could shoot a ping pong ball.

Gotcha! I wont waste my time then. I did make a modified potato gun into a golf ball canon... works REALLY well...almost too well

[boilerman856]

How deep of a vacuum did you have to achieve for this to work and what size pipe did you use?

Sent from my XT907 using Tapatalk 2

[doc havoc]

Didn't use a micron gauge, just pulled vacuum until there was little to no air coming out the exhaust of the pump. The pipe is 1-1/2" abs. The ping pong ball barely fits. If we put the ball in the pipe and lift one end, it takes the ball about 6-8 seconds to roll to the other end. We used packing tape to make the seal on the ends of the pipe and then wrapped with duct tape to keep it sealed.

CAUTION: Do not stand directly behind the cannon. Our tape let loose one time on the discharge end and the ball came out the back end. Nobody was hit, but it did catch us off guard.

[mayguy]

I didn't have this fun back then! :-)

As I was watching the video, I was thinking, "How does that work!"? then saw your post later!