There are many variations to the common potato gun. This section
discusses some of the most common variations to the standard potato gun.
Using a T or Y joint, the combustion chamber will have two endcaps on it. The purpose of this modification is to capture combustion byproducts or the byproduct of the evolution of your propellant. I know, you're saying "What?!" For example: Combining bleach and calcium carbide will evolve Oxygen and Water. The Oxygen is useful in combusion, water is not. Combining the two in the T-Shaped chamber allows the water to fall to the lower portion of the chamber so it won't impede the reaction. This chamber also has other applications; use your imagination.
This time, the combustion chamber is made out of a 180' drain trap to double it back upon itself. The advantage: Space saving, and it looks cooler.
Bolts are an effective means to add strength to your joints. They're especially useful if you intend on using the higher-order propellants. You simply need to drill holes for as many bolts as you wish, coat the bolt with plenty of sealant and use a nut on the inside to hold it in place. This should give you more piece of mind when doing those big time shots :)
A variation I have thought of but not yet employed:
The idea: A way to remotely aim and fire the potato gun.
Implementation: The potato gun fits into a harness. The harness is
constructed out of wood. Two RC car motors are used to swivel the gun on
its base, and raise/lower the barrel. Ignition is electric to allow for
the remote firing.
I don't know enough about Pneumatics to write this section. I would
like someone else to help me fill this in. If you'd like to write this
portion of my page, please send me email. I would like a very thorough page,
but there are no limits on it. Thanks!
This section includes 3 diagrams which will aid in your understanding
of the construction. Text users can download them by downloading these
three links:
SILENCE1.GIF SILENCE2.GIF SILENCE3.GIF
The principle behind a silencer is simple. The expanding gas in a gun reaches the end of a barrel. When this happens, the gas expands in all directions in a sort of shock-wave. The resulting wave of compressing and expanding gas reaches your ear as a bang.
The objective then of a silencer is to prevent the gas from freely expanding in the air by instead allowing it to slowly expand within the silencer. This is achieved in commercial silencers by porous metals and controlled air flow. Because we can't expect to be very technical, our silencer is a basic model of this principle which you can easily build from the same materials the gun is made from.
Note that these are only plans for such a device. I have not
constructed one nor do I plan to. This device may be illegal where
you live, or it may not work at all. I can't vouch for it.
(*) You may have to alter the diameter of the pieces to match the specifications of your gun. You shouldn't need to buy any new piping, use the leftovers from your barrel and combustion chamber.
(**) Don't forget, if you have a lesser diameter on any of these
pieces that you ought to increase the length to compensate.
Assembly:
First and most importantly, the inside of your coupling sleeve
and the outside of your guns barrel need to be threaded. This
is because you do not want to permanently affix the silencer to your
gun for various reasons.
1) After having the threading done, use your piping glue to glue the piece of 10" long, 2" dia. piping into the non-threaded end of the coupling sleeve.
2) Once that has set, slide the 4"->2" reducing bushing down until it is flush against the coupling and the 4" end is open opposite the coupling sleeve. Apply glue, and allow to set.
3) Using a drill, drill many (how many is up to you, but not TOO many) tiny holes into the 10" piece of piping. Use the smallest drill bit you can find (I don't have any suggestions), or else you'll end up turning your potato into french fries when you fire it. These holes allow the air to expand before exiting the barrel.
4) Next, glue the 4" dia. piece of pipe into the open end of the bushing. You should have a pipe within a pipe now, otherwise you got confused somewhere. Allow the glue to set, as usual.
5) Jam that foam or sponge into the area between the two pipes.
The tighter, the better. This silences and slowly allows the air to
expand as it hits it. This is what will absorb the bang.
All told, you should have a functional silencer. I do not know the
exact length of the coupling and bushing, so you may need to shorten
(or length!) the 2" dia. pipe to make them even. When attached,
it will look like you have a gun with two combustion chambers. It
may be necessary to use something to hold the foam (or sponge) in
the silencer, I haven't a clue.
One of the things I've often wanted to be able to do was track my shot. There have been a
few ideas tossed around but you have to keep in mind when you're tracking your shot:
Will I be starting a forest fire with this?
Can it be seen in the day as well as the night?
Is it even going to work??
Thankfully I've answered all of those questions already. Here are a few means to use to
safely track your shot.
Finally, an answer to the much posed question:
I still get conflicting email about this issue on a regular basis. I've decided to throw what Ace Hardware told me out the window; most people seem to disagree with them. Instead, I'll be quoting what I've been told in an email.
There are really only two important differences between PVC and ABS piping (besides the color). First of all, ABS is more expensive and more difficult to find. Secondly, ABS is more rugged than PVC. It will crack cleanly (when it breaks) where PVC shatters. ABS also won't degrade from exposure to sunlight and temperature extremes as much as PVC will.
My recommendation is: If ABS is feasable, then use it.
For most people, PVC piping is still completely safe. The differences are important for more powerful guns. If it's safety you're worried about though, then I suggestion you read on.
THE WEAKEST PART OF YOUR GUN IS THE JOINTS.
I cannot stress enough how vital they are. While the gun can stand 270
PSI the joints cannot come near that. Many people have written saying
that their gun "exploded" and pulled apart at the joints in a powerful
shot. I've never heard of anyone's gun bursting because the pipe failed
to hold. When you build your gun, keep this in mind: Your joints need
to be assembled properly! A common habit is to cut corners, well
don't! For a few extra dollars, buy the pipe cleaner and clean the
joints before gluing. Buy the purple primer and prime your joints.
Lastly, cement the joints right. Slide the pipe in firmly. Wipe off
excess cement, and let the cement cure completely before you go and put any
pressure on them. That includes the pressure of pressing another fitting
on. If you're concerned at all about the safety of your gun, the above
is much more important than, "Am I using PVC or ABS?"
Mounting your sparker on the side of your chamber adds considerable
weakness to the chamber and invites disaster. However, such a position is
favorable because it can ignite your propellant from the center rather
than the end. The result: faster burn. But how can you mount the sparker
in the side-center of the chamber if it's a safety hazard? The answer:
Put a T-Joint in the center of your chamber and mount the sparker in an
endcap on the T. This is far safer than mounting the sparker directly
into the side of the chamber.
Yes, one of my pet peevs. When you build your gun, don't skimp on your joints. Remember to:
I received an email from Steven Yahn, syahn@tscnet.com, which supports what I've said above as well as offering great inside info on pipe joints. Please click
You're probably asking 'why do I need to know the weight of my propellant?' Well most importantly, you should know if your propellant is heavier or lighter than air. Although this is really only useful for people who fill their chambers by unscrewing one end, I'm sure others can put the data to use.