The potato cannon powered boat
(work in progress... probably abandoned)

The CAD drawing of the boat's PVC parts

It's a boat of sorts that will float.  It certainly won't carry anything beyond basic needs. Potato cannons are powerful, but this is a very different application of the explosive power. Making it float stably will be tricky. I doubt the sealed PVC tubes will be enough. I see my two best alternatives as being wood and pool noodles. The latter I can probably get from Pioneer's robotics team. The long barrel at an angle is the propulsion system. The large diameter pipe section at the top will be where the combustion (hairspray and oxygen) takes place. The air will expand through the barrel and into the water.

My bro and I tested his potato cannon (sans potatoes) in a tub of water one afternoon. I think the recoil should be enough. Interesting to note, is that the barrel, if airtight, fills partly with water, so when we pulled the barrel out, a quart or so of water poured out! This problem will be taken care with already existing ideas.

A one-shot boat would be boring... Obviously it only has one barrel, so no multi-barrel firing. The solution is indeed a "reloading" mechanism. My method for acheiving this is largely documented by pictures below.

Of what is shown in the picture at the top of this page, it'll disassemble into two parts, the rectangular base and the cannon barrel itself. I'll probably use a screw through each of the top two red connectors to hold the barrel in position.

So what have I built so far? I've built the above gearbox, it works well with 3volts or more.  I've started building a control box for the contraption.  I've cut all the PVC pipe for the cannon as well.  What's left is wiring and machining parts for the combustion chamber.  I'll also need to do the mount for the can of hairspray.

To control the contraption, I have a control box that looks a wee bit much like a detonator for a bomb...  Nevermind that it was machined on school property too.  There are two controls on it.  First is the piezoelectric igniter: generally what's used on gas grill.  That thing is neat... Shocking one's self is fun.  It also makes a nice 1cm spark between it's two wires.  The second control is a three-way switch, pilfered from the controls of FRC1015's first control board (for the 2003 robot).  It took me a while to figure out how to properly wire that.  The actual 'box' is two 2x4's that I hollowed out with a milling machine and then screwed together.  The top is covered by 1/16" aluminum, with holes machined for the igniter and the switch.  Out the bottom are 6 wires, two for each direction of the switch and 2 for the igniter. An Eye-bolt is screwed into one side of the box and a nylon tether is anchored there.  The wires will be wrapped/attached loosely to the tether.

I know for a fact that the igniter's spark is strong enough through what amounts to about 50 feet of wire.  (Thus, I have a 25' leash on the boat)  It is, however, a significantly weaker arc.  The igniter's wires go to two nails that are screwed into the barrel.  The tips of the screws are very close to each other within, allowing for the arc which will ignite the hairspray.

The total length of 1.5" PVC used is just under 25'.  When I went to Stadium Hardware to buy the PVC, I had planned to buy 25', but bought 30' since the last 5' only cost an additional amount somewhere under $2.  I hadn't done any math beforehand, so that 25' estimate was amazingly close to what I needed.  I salvaged some of the connectors from an old archery target support system. The rest I bought.  The cutting of the PVC was all completed on a Saturday visit home from the dorm.  It fits together almost perfectly (i.e. a few imprecisions of >=1/16", but I've yet to glue stuff together (though I think it's safe for me to start doing so).

The CAD work that I did for this only involved how to put the PVC together.  I approached the CAD part of it by building the individual lengths of pipe and the connectors, and then assembling them from their separate files.  Initially, I designed the parts from memory, guesstimating various measurements.  When I returned home, the same weekend I did the cutting, I spent most of my time at home actually measuring pieces and updating the drawings.  That work payed off: every cut was right the first time.

I had some definite inspiration for starting this project.  The first of these was my brother's potato cannon.  He built it early during the summer with help from one of his fellow Boy Scouts.  Needless to say, firing chunks of potatoes a few hundred feet is great fun.  In part, I didn't want to be a complete copycat, so I started thinking of other ways to apply that method.  I eventually ended up here.

The other big source of inspiration was money, or rather a gift certificate, and the need to waste it.  It's not every day you get a $50 gift certificate from school!  For that I thank my Drafting/CAD teacher, Mrs. Porter. The gift certificate (to Stadium Hardware specifically) was an award for CAD/Drafting student of the year.  CAD was one of the funnest classes I had in high school...

Archived versions: -9-22-06