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Monday, March 28, 2011

2011 Trebuchet for Chunkin' Pumpkins

The idea was to build a trebuchet.   This is a catapult type device with a sling that throws objects like dead beasties over the castle walls in the days of knights and non bathing.  A television show of the '80s, Northern Exposure, gets the credit for Count Ferrari's enthusiasm.  That particular device threw a piano a LONG way.

Our device only has to hurl an 8lb pumpkin 800' for us to win. is a very fine website with some math behind a predicted performance.  Just plug in the numbers and adjust to see how far you can throw an object.

There is a competition in Burlington, put on by the Parks and Recreation division.  There is another competition in Snohomish within a week too.  Both of these contests attract 5-8 different trebuchets and we intend to enter the contest that tops out at 800'.  There is another contest to 1600' but for our first run at this we will go for the 800' contest.
Lucky Dave with his head cut off for security purposes.

I mentioned my pursuit to my disc golf friends from Anacortes and Bellingham and they were instantly in!  We talked about resources and since Lucky Dave worked at Marine Service Center, he mentioned they had quite a bit of scrap steel from yacht delivery cradles.  I went and talked with the owner, Jim Rard, and he also had been planning to build a trebuchet for some years and this was the impetous he needed to get going on it.

Jim Rard of MSC looking at the 27' mast section for our throwing arm.

In the yard of Marine Service Center in Anacortes were all the ingredients for our creative, if bent, minds.  We found a platform that is roughly 6' x 10' built of welded 2x4 steel members and even has feet under it for easy forklift pickup.

Additionally, we found an axle system in a set of wheels used for some sort of caster like application.

The axle in the rough.

The axle minus the wheels.

The axle sitting on our platform.

Count Ferrari cleaning out the old
grease from the axle.

Many steps and designs were gone through but we are working with the guiding principle of K.I. S. S.  (Keep It Simple Stupid).  We originally had an A frame of steel but discarded that for a vertical post that is stayed with SS cable and turnbuckles to fit our nautical theme.  (There is a contest for theme and one for the crowd's choice as well).
Cole messing about on the platform.
The axle assembly is slated to be approximately 10' in the air between the two stayed towers of 4x4 steel.  We are hoping to melt down lead to power the beast as MSC has a melting pot just for the lead forming.  Lead is very heavy per cubic dimension.  708 lbs per cubic foot!  Jesse, Jim's 17 year old daughter, calculated the plate weight of 18" dia plates 1" thick to be 104 lbs.  So if we had 20 of those we would have 2000lbs + powering the pumpkin in a very small compact load.  We figured the weight of each plate to be the most we would want to pick up.

We have high hopes as Jesse manipulated the numbers we had, weight of mast, weight of plates, height of axle, length of sling, etc... at the virtual trebuchet website mentioned above and she came up with a theoretic distance of 1100 feet!  We shall see how accurate that predictor is when we finally get it built.
Jim on the left and the Count on the right,
both checking the spar section.
It weighed in at 125 lbs or 4.5lbs per foot.

Count Ferrari and Lefty are both growing white pumpkins at their estates.  We are hoping to produce many 5-8lb pumpkins.  The white pumpkins are superior since the wall thickness is far greater than the orange pumpkins.  For practice we are hoping to find some 5-8lb bowling balls.  We can reuse these easily.  There just happens to be a nice flat field next to Marine Service Center for testing, or we can just throw floating things into the bay!

The contest in Burlington is the 3rd week of September and the Snohomish contest is one week this side or another.  We hope to be throwing by May and totally dialed in by August.  Our theme is being worked on by Hawkeye and Jesse.  Pictures to follow.

The rigging is donated by Counter Current Marine owned by Ian Sloan.  Stranger,owner of Joyful Creations is sewing up the sling and will be doing the You Tube for us.

That is all for the nounce.  More to follow soon.

Submitted by Count Ferrari

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