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Potato cannon carriage #1: Frame/axle and elevating arcs

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Blog entry by JJohnston posted 07-25-2010 06:12 AM 5495 reads 4 times favorited 11 comments Add to Favorites Watch
no previous part Part 1 of Potato cannon carriage series Part 2: Frame and elevating arc assembly and trunnion construction »

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 other parts. These would only be guidelines, naturally. I used AutoCad to draw and dimension everything.

We built the cannon first. It’s a 36” x 2” barrel and a 14” x 4” combustion chamber. The wheels (from McMaster-Carr) are 20”. Try as I might, I could not find a 20” wheel with a solid rim to simulate the real thing.

This is the beginning of the axle, or the frame. I don’t know the correct names for many of these parts, so I’m making them up. It’s 1/2” baltic birch ply, with lightening holes, top and bottom, and 2x lumber milled square to 3 1/2” wide for the sides.

This shot shows the “trail” in the towing position. We’re not actually going to tow it.

This is the trail in the firing position. There are 2 bolts in each arm, one farther back for the pivot, which will be secured with a nut, and one close to the forward end, which will come out, and drop into one of two holes, for each position. These pieces have been ripped a hair narrower than the frame side pieces so they will pivot easily.

Next are the elevating arcs. You can see these in the picture of the real thing. This is also 1/2” baltic birch ply. The curved slot is a circular arc, centered on the 3/4” hole on the upper right; the trunnion (cannon’s elevation pivot) drops into the hole, and there will be a hanger stud sticking out of the trunnion assembly and through the slot, with a locking knob on it. The arc goes from -10 to +45 degrees, so when the piece is resting on the trail, elevation range will be about 0 to +55 degrees. My lightening holes are unevenly spaced; that’s what you get when you eyeball rather than measure. I did all the cuts with both pieces double-side taped together.

Same shot; you can see the “trunnion bearing cap” in place here. The bearing blocks & caps are 2x lumber, milled square. The trunnion is a piece of 3/4” threaded rod. It will wear these holes out, but it’s not going to be moving very much, and there’s very little weight on it, since the hanger studs and knobs will be right near the cannon’s center of gravity, so I’m not worried. If they get bad, I’ll drill them out and put in a bushing.

Next installment: Frame/elevating arc assembly and trunnion.

-- "Sometimes even now, when I'm feeling lonely and beat, I drift back in time, and I find my feet...Down on Main Street." - Bob Seger



11 comments so far

View RonPeters's profile

RonPeters

708 posts in 1575 days


#1 posted 07-25-2010 06:42 AM

What a cool idea! A nice way to show the nephew there’s more to life than video games.

-- “Once more unto the breach, dear friends...” Henry V - Act III, Scene I

View wseand's profile

wseand

2442 posts in 1737 days


#2 posted 07-25-2010 07:17 AM

Well I have to say that will be the epitome of potato canons. And that is very typical of the Howitzer, that one is the M101 Howitzer from WWII era and continued service in Vietnam. It’s main use now is ceremonial.

-- Bill - "Freedom flies in your heart like an Eagle" Audie Murphy

View 559dustdesigns's profile

559dustdesigns

632 posts in 1863 days


#3 posted 07-25-2010 09:42 AM

I remember the one and only potato gun I ever had. I never saw it again after shooting it at a friends house, he lived on the gulf coarse. I still don’t think it was that bad cause we yelled “FORE” first! LOL. This should be great fun to build. Can’t wait till your next installment. Thanks, The trouble maker

-- Aaron - central California "If you haven't got the time to do it right, when will you find the time to do it over?"

View ajosephg's profile

ajosephg

1854 posts in 2256 days


#4 posted 07-25-2010 12:42 PM

That will be a BLAST!

-- Joe

View stefang's profile

stefang

13334 posts in 2029 days


#5 posted 07-25-2010 12:55 PM

What a fun project! I can’t wait to see what you come up with as the blog continues. One of these would look great in the garden too (not going to happen according to the wife).

-- Mike, an American living in Norway.

View CaptainSkully's profile

CaptainSkully

1190 posts in 2253 days


#6 posted 07-25-2010 05:23 PM

Very cool! I built this calcium carbide cannon from these plans.

-- You can't control the wind, but you can trim your sails

View Dennisgrosen's profile

Dennisgrosen

10850 posts in 1810 days


#7 posted 07-25-2010 09:58 PM

this is going to be interresting
I maybee need one to the next war with the kids…....LOL

Dennis

View Howie's profile

Howie

2656 posts in 1618 days


#8 posted 07-26-2010 12:38 AM

I like the carbide cannon idea. Looks like a great way to rid the world of load stereos!

-- Life is good.

View RonPeters's profile

RonPeters

708 posts in 1575 days


#9 posted 07-26-2010 08:07 AM

Hello?

Um… Mr. Johnston? This is the police. We’re calling because we had a report of a potato…

;-)

-- “Once more unto the breach, dear friends...” Henry V - Act III, Scene I

View JJohnston's profile

JJohnston

1586 posts in 1986 days


#10 posted 07-26-2010 02:16 PM

;-) I checked my city ordinances first. There’s a section titled (paraphrased), “Propulsion of Missiles”. It essentially says not to launch “rocks, paint balls, water balloons, etc. in such a way that is reasonably likely to cause harm to persons or property.” I’m right on the outskirts of town, and there’s a nice high spot overlooking a wide, shallow valley with nothing but scrub brush. It’s the perfect potaton cannon range.

-- "Sometimes even now, when I'm feeling lonely and beat, I drift back in time, and I find my feet...Down on Main Street." - Bob Seger

View 559dustdesigns's profile

559dustdesigns

632 posts in 1863 days


#11 posted 07-28-2010 10:11 AM

I’ve seen those pumpkin chuckin competitions on Tv, the ones where they shoot pumpkins 3000 feet.
Why not start one with potatoes.
You could have the raw potato class and the baked potato class. LOL

-- Aaron - central California "If you haven't got the time to do it right, when will you find the time to do it over?"

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