The left part of my brain was saying, "Hmmm, a catapult... Can we even do that? The school has a zero-tolerance weapons policy. But as long as she has the OK from her teacher, then that could pose some very interesting math and physics problems for her to overcome, and would require quite a sturdy structure.
What should we use for materials, and just as importantly, what types of joinery should be utilized to reduce the risks of failure from high impact lateral forces?"
The right part of my brain said "A catapult! Hell yeah!"
So here's the deal I made with her.
1) She does all design work, calculations, and as much of the actual building and construction as I deem safe for her to handle.
2) We do not use real rocks or boulders as projectiles. We will carve and paint styrofoam blocks to LOOK like boulders, but anything that can cause harm to people or property may NEVER be launched.
3) We will design a series of fail-safes and locking mechanisms that will prevent anyone from using the catapult when it is not under the watchful eye of her or one of her teachers.
4) I get to put goofy bumper stickers and slogans on the back of the thing when it's done (more on this later)
She accepted my deal, and immediately went on the internet to research designs and the physics of the catapult.
The style that she chose is known as the Mangonel
Mangonels fired heavy projectiles from a bowl-shaped bucket at the end of its arm. The Mangonel was used for aiming various missiles at castles, fortresses and cities. This type of catapult was easy to construct and wheels were added to the design to ensure manoeuvrability. The Mangonels were capable of firing projectiles up to 1,300 feet.
One of the interesting things about Mangonels is that they didn't just launch rocks. According to several of the websites Rachel researched, The Mangonel could launch missiles across long distances. Attackers were ingenious in their ideas for launching projectiles which would cause distress and discomfort inside the castle walls. Mangonel missiles included the following:
- Stones
- Sharp wooden poles and darts
- Fire
- Casks of Burning Tar
- Burning Sand ( this became trapped inside armor )
- Pots of Greek Fire
- Dung
- Disease ridden bodies
- Body parts
- Dead animals
- Any rotting matter
- Quicklime
- Dead, sometime mutilated, bodies (often peasants from outside the castle perimeter)
That last one kind of gives new meaning to the phrase "Serf's Up!"
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Anyway, back to the construct:
Once she picked a plan and drew it to scale, we had to figure out a launching mechanism. Since the catapults of that time used sinew to create the torsion needed to spring the arm forward, and a few thousand feet of the stuff was hard to find (and out of our budget), we opted for rubber surgical tubing. Highly stretchable, cheap, and easily obtainable through Amazon.com
The rest of the supplies - mostly wood - was either already in the garage, or was picked up for just a few dollars at the local home improvement store.
(as a side note, it seems kind of ironic that one would go to the "home improvement" store for the materials to build a weapon designed to destroy a home).
With plans in place, we set out to build. Started by measuring and cutting the 2*6 lumber we were using for the chassis, followed by the wheels and winding guides.
We decided to use pocket-hole joinery for the chassis. Yeah, I know that's not very historically accurate, but we needed something that
1) she could do easily and accurately
2) provided a strong joint
3) we could easily disassemble/reassemble as needed until the unit was done, and then add glue for the final build.
Using the KREG pocket hole system, Rachel assembled the entire chassis (and learned a new skill!)
The wheels and guides were made from a sheet of 5/8" OSB, that was cut into six 16" x 48" strips. Those strips were stacked 3 high and glued together into 2 pieces, which were then cut into six 16" x 16" x 1.875" squares.
The squares were then cut using a circle-cutting jig on the bandsaw into four 15" diameter wheels, and two 10" diameter winding guides.
Here's Rachel at the band saw cutting the wheels with the circle-cutting jig.
Finished wheels, stacked and ready for drilling the holes for the axles.
Rachel used a 1" spade bit to cut the axle holes in each of the wheels. We used the dimple left by the circle-cutting jig to ensure that each of our holes were dead-center.
--------
Anyway, back to the construct:
Once she picked a plan and drew it to scale, we had to figure out a launching mechanism. Since the catapults of that time used sinew to create the torsion needed to spring the arm forward, and a few thousand feet of the stuff was hard to find (and out of our budget), we opted for rubber surgical tubing. Highly stretchable, cheap, and easily obtainable through Amazon.com
The rest of the supplies - mostly wood - was either already in the garage, or was picked up for just a few dollars at the local home improvement store.
(as a side note, it seems kind of ironic that one would go to the "home improvement" store for the materials to build a weapon designed to destroy a home).
With plans in place, we set out to build. Started by measuring and cutting the 2*6 lumber we were using for the chassis, followed by the wheels and winding guides.
We decided to use pocket-hole joinery for the chassis. Yeah, I know that's not very historically accurate, but we needed something that
1) she could do easily and accurately
2) provided a strong joint
3) we could easily disassemble/reassemble as needed until the unit was done, and then add glue for the final build.
Using the KREG pocket hole system, Rachel assembled the entire chassis (and learned a new skill!)
The wheels and guides were made from a sheet of 5/8" OSB, that was cut into six 16" x 48" strips. Those strips were stacked 3 high and glued together into 2 pieces, which were then cut into six 16" x 16" x 1.875" squares.
The squares were then cut using a circle-cutting jig on the bandsaw into four 15" diameter wheels, and two 10" diameter winding guides.
Here's Rachel at the band saw cutting the wheels with the circle-cutting jig.
Finished wheels, stacked and ready for drilling the holes for the axles.
Rachel used a 1" spade bit to cut the axle holes in each of the wheels. We used the dimple left by the circle-cutting jig to ensure that each of our holes were dead-center.
That's all we were able to accomplish on day one and two. We moved the parts into the shed for now, and will get back to it next weekend.
Bon Appetit, and Have Fun Storming the Castle!
-Steven
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