| Blog series by JJohnston | updated 950 days ago | 7 parts | 18475 reads | 72 comments total |
Part 1: Frame/axle and elevating arcs
Recently, I thought I would try to get my nephew, 9, away from his video games, so I proposed that we build a potato cannon together. Grandpa was not very keen on the idea of us firing it handheld, so in order to placate him I agreed to mount it on a carriage. I chose the 105mm Howitzer as a model. This is pretty typical as light artillery pieces go, I think. I scaled various relative dimensions from pictures, and once we got our cannon built, used those relative dimensions to size the...
Part 2: Frame and elevating arc assembly and trunnion construction
This weekend consisted mainly of painting, painting, painting, some more painting, and after that, some painting. I’m using canned spray paint from the big box store, and the wood just soaks it up. It takes a good 3 coats before I can scuff sand paint without also sanding wood. Here’s the frame with the elevating arcs attached to the sides, and the axle going through. It’s a 5/8” threaded rod, 24” long. The box stuck to the side of the left arc is to hold a br...
Part 3: Trail, ramrod and major assembly
We made a lot of progress today. Most of the painting is done, so we could concentrate on assembly. Here’s the lower trunnion assembly with the hanger studs and knobs complete. The potato projectiles are muzzle-loaded, so they have to be pushed down toward the combustion chamber with a ramrod. The ramrod will ride in a tube above the barrel, both to simulate the “recuperator cylinder” on the real thing, and because it’s so long, there’s no other place to put it. ...
Part 4: Ignition
Ignition is via a 100,000 volt stun gun connected to the electrodes. The stun gun has a sliding on/off switch on the left side, and a momentary contact rocker switch on the right. I carefully pried the rocker switch body out of the housing and disconnected the wires. I then removed the guts from the switch housing, cut out a small rectangle of acrylic the same size as the bezel on the switch housing, drilled a hole in it big enough for the lamp wire I’m using for a remote switch, and su...
Part 5: Forward armor
First, I didn’t like the way the ramrod just stuck out of its tube, as shown in part 3, so I made a longer one that fits the rod completely. I put a small eye screw with a keyring in the end of the rod so I can fish it out. The tube now has a cap on both ends; I put a light chain on the access cap to keep it from getting dropped or lost. I’m not super happy with how chunky the forward tube bracket is. Now I’m starting on the armor plating. The “armor” is 1/...
Part 6: Some tweaks and the test firing
I made a few little improvements this week while I’m finishing the forward armor. I redesigned the forward ramrod tube bracket. It’s as minimal as I could get it – a 3/4” piece of poplar, cut to fit between the tubes, and a hose clamp. This lightens up the front end, both visually and literally. I also reattached the cap chain with a ziptie right behind the cap, which shortens/cleans it up. A shot of green paint and everything looks fine. I had a vision of ki...
Part 7: Artwork and final assembly
It’s been a while, but it’s worth the wait. I asked a friend of mine, who’s a talented sketch artist, to draw up some artwork reminiscent of World War II bombers. I asked for something in the style of Slim Pickens riding the bomb in “Dr. Strangelove”, and including the name I chose for it, “Devas-tater”, and after some fine tuning, this is the finished product. I’ve been using it as my avatar for the last couple of weeks. The “Mr. Potatohe...
