Both potato cannons worked as expected. They survived both the trip up on top of the van as well as the weekend abuse of being fired and left out in the rain.

Here are some clips of the pneumatic cannon:

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Range was approximately 75-100 yards. Given the tank was not designed to hold pressure and I was only going to put so much faith in the duct tape, I never ran it above 70 PSI. Will be looking to double the PSI as well as the length of the barrel for next year.

That puff of smoke you see coming out of the barrel is actually just moisture from the compressed air. Adds to the effect however.

Here’s the stun gun cannon fired during daylight hours:

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Range was probably closer to 150 yards. We timed how long the potato would remain airborne, and seemed to consistently run around 15-18 seconds when fired at a 60 degree angle. Will need to do some math to calculate what that works out to for distance and initial velocity.

Here are the two types of hairspray I found worked best:

The can on the right consistently produced the longest distance throws, but generated the smallest amount of flame in the chamber. Here’s an example. Note the most cool “thoomp” as the potato fires.

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The can on the left produced slightly shorter throws (maybe by 10 yards or so), but produced the most spectacular light shows. Here’s an example:

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My daughter was handing out glow stick bracelets. Turns out it produced just enough light to find the stun gun controls. That’s the bit of blue you can see moving around in each of the last two vids.

So that’s about it for now. At the recommendation of a friend I picked my son up a copy of Electronic Gadgets for the Evil Genius. May have some additional cool projects to post from that in the future.

Oh ya and the 10 ft catapult sitting in my back yard, plan on continuing work on that as well.

Chris

The pneumatic cannon is complete!

Ran a pressure test on the tank this morning. Filled it to typical tire pressure and let it sit for an hour. Needle on the gauge didn’t budge. This is a good thing.

Here’s the completed unit:

After sleeping on it, I was starting to think that maybe the warning/suggestion on the side of the tubing might apply to me as well. With this in mind, I decided to pull out “The Handyman’s Secret Weapon” to provide some structural reinforcement.

See, all fixed! Warning label gone!

You can do some amazing projects with duct tape. About the only thing it isn’t good for is sealing duct work.

We *finally* have some dry weather, so I decided to try a test firing at low power (20 PSI) just to see how it works. Here are the results:

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That’s about it for now. I’m off on vacation, but will try to post some more snaps when I return.

Drive fast and take chances,

Chris

Note the section circled in red. Keep in mind this is the air chamber that will get pressurized just before firing the pneumatic cannon.

I’m sure they did not intend for that warning to apply to me. I’m a professional after all.

Out of time to test it today so I’ll find out in the AM if that warning really means anything.

C

My daughter decided the potato cannon stand needed a bit of color. Here are the results:

Looks a bit to me like camouflage from the Avatar movie, but I’m not a pre-teen.

Also decided to RTV over the electrical connection on the potato cannon. This will reduce the chance of someone getting shocked. Not very likely, but better safe than sorry.

Also started work on the pneumatic cannon. Decided to keep it small so that I can finish it in time. The air chamber will be made up of 3″ PVC. I can then use a “T” connector to a ball valve and 1.5″ PVC for the barrel.

I started by gluing a female threaded connector to the barrel. This allows me to separate the barrel if I need to clean out an obstruction.

To this I’ll connect a male threaded connector, and then use various adapters to get me to a threaded nipple. This will be needed to connect to the ball value. Here’s how the parts will lay out, with the barrel on the right.

I’ll use a similar set of adapters on the other end of the ball valve. This will connect me to the “T” connector, to which I’ll attach 3″ PVC in order to form the tank. Here’s some snaps part way through the gluing process:

And yes I’m remembering to tape all of the metal to metal connections. 

Note the air tank section above only has one cap. This is because I have special plans for the other cap:

The top component is an air gauge so I can monitor pressure in the tank. The bottom component is a standard air valve for an automobile tire. Usually these just pop into place, but I decided to go with one that is threaded so I can use a nut to lock the connection point firmly. A bit of lock tight on the threads, and hopefully I’ll get an air tight seal. One of the problems with this build is that any air leaks pretty much requires that you throw half the unit away and start over. Want to do it right the first time.

So here’s where we are at so far:

Give it the day to dry and I’ll be able to check for leaks and do a test firing this evening. Total build time was just over an hour. Soooo much easier than a 10′ catapult!

C

Before the rain descended, I was able to get in some test firings with the kids. Here’s some Quicktime vids with the results.

First, the good news. The potato cannon works as expected:

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The catapult works, but will need some structural tweaking before I can ramp it up to full power (sorry for the sideways vid):

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However here’s my problem; that test firing was on Sunday and it has been raining non-stop since then. I estimate I have at least another 4-8 hours of work to do before I can crank the catapult up to full strength. Given the catapult is 10′ tall, that means I have to work on it outside. Weather report calls for non-stop rain. Yesterday ended up being a complete wash, with today looking the same. Out time for the trip is in less than 30 hours.

Soooooo, think its time to punt…

I’ve decided to hold off on the catapult till next year. This gives me more time to work out the kinks, and keeps me from rushing things which can only end badly.

Aaron suggested I try a pneumatic cannon. If you have no idea what that is, its a potato cannon based on air power. You fill a tank with compressed air and quickly release it. The release is what actually fires the potato. Think I could build a decent hand held unit in one night, so I’m off to Home Depot now to snag some parts.

So the catapult is off line for now, but the saga continues…

C

Decided I wanted to build a stand for the potato cannon. Figured this way you don’t have to wrap your arms around it during ignition. More distance, the better.

Here’s the basic design I came up with:

and here it is with the potato cannon in place:

The wooden dowel used to set the firing height is also the plunger used for pushing the potato down the barrel. Wahoo, one less part to transport.

My daughter has expressed an interest in painting some of the components. I’ll worry about that a little later after she wakes. For now, there is a huge beast at the door beckoning to me, and I just have to answer…

More to do, more to come,

C

Assembled the unit outside of the shop and here’s what it looks like:

Pretty funny as the top is almost level with the window on the next floor up.

Now that’s its built, I’m convinced that top bar is not going to stand up to the abuse.  As much as I hated to do it, I partially disassembled the catapult (again!) so I can add two supports in the front. Once the glue is dry I’ll be able to reassemble. Of course I can always find something else to do while that’s happening, like building the throwing basket.

I like this design soooo much better. Its lighter, feels stronger, and I was able to shape a nice ark in the top to put a bit of spin on objects that get tossed.

Here’s a straight on view. The “arms” to the left and right will be bungee cord attachment points. The throwing arm will get glued to the bottom.

Getting down to the wire, so its time to get back to work.

Cheers,

Chris

Compared to the catapult, the potato cannon barely seemed like a project! Only took a few hours, in fact my wife completed the assembly while I focused on the beast.

The secret to a good potato cannon is getting a clean insertion that provides an air tight seal. Any air that can sneak by is air not propelling the potato further down the barrel. I tapered the top of the barrel so that the potato will get cut cleanly as its inserted in.

Here’s the full unit with a good proportion of scale.

And a close zoom on the ignition source.

I was thinking about taking the unit apart and wiring the activation switch to a remote box. This would permit me to build a console that had the kids feeling they we launching a ballistic missile. Given time constraints however, that project will have to wait.

Next step is to RTV the electrical components. Then I just need ammo and fuel to do a test firing!

For any sane person, trying to design and build a 10′ catapult in less than two weeks while still maintaining a job and a life would be more than enough….for a sane person…

Hey, I need something to do while the glue is drying on the other project.

This one should be easier as I actually found some directions. In typical guy format however I promise to skim them once, put them aside, and then wing it to make it even bigger and badder.

Here’ are the rough parts:

I’ll use the 3″ clear PVC for the initial expansion chamber. The 2″ clear PVC will be for launching the projectile. The device in the middle? Oh that’s a 300,000 volt stun gun. Figured that should get me some decent ignition.

Using a couple of metal screws for firing electrodes. Figured these should hold up to the arching and firing. Used a #2 pencil to set the spark gap. Reminded me of setting the points in the old muscle cars I used to restore. Yes I realize the electrodes are a bit off. Used to have the same problem in one of my old Mustangs.

Glued up the assembly and will let it dry while I switch gears back to the catapult.

More on this to come as well.

C