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Trebuchet load calc

Started by shinnlinger, March 14, 2012, 02:13:01 PM

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shinnlinger

Hi,

A student of mine is building a trebuchet in class and he wants to use a 1000 lb counterweight an a 12 ftish throwing arm. We want to put a swinging counter weight 1/5th of the way in from the end (about 2ft 4inches).  How big should the throwing arm be?  He has a woodmizer (lt 30)at his house and can cut just about any size, but is limited to white pine or possibly spruce.  I am suggesting a taper cut but that might just be silly.

I was hoping to work Dons calcs on it but I cant find the the correct app in the tool box.

Thanks.

Dave
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

zopi

Google "mac treb" also, a good book is Sir Ralph Payne Galway's treatise on seige engines.
Got Wood?
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zopi

Never mind.
http://www.algobeautytreb.com/
Not sure if that will help with the throwing arm...but there may be some links to help.
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Brian_Weekley

I have no idea.  But, COOL!  Everyone should have a trebuchet to hurl things. :D
e aho laula

zopi

funniest thing I have seen thrown...a urinal...half a mile...
Got Wood?
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beenthere

Being as how white pine grows with whorls of branches at nodal locations, I wouldn't trust it as an arm for trebuchet. I'd instead cut boards or dimension and laminate the arm.

Time to calculate the moments involved and the loads that will be applied. Are you teaching any engineering of beam strength in class?  Maybe the math teacher can help and a great teaching lesson can happen.
south central Wisconsin
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bill m

Rick Brown of the Handshouse in Norwell Mass. has made one. He should be able to give you the info you need.
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Brucer

Funniest thing I have seen (pictures of) thrown...a dumpling. :D

Many years ago a German housewife became incensed at the US jet fighters taking off at full throttle over her house. So her husband made her a catapult and she devised a recipe for a particularly sticky dumpling. She'd fire these at the offending aircraft as they took off.

Everyone who saw it thought it was great for a laugh -- until she got her aim and started hitting the cockpit canopies. It got her hauled into court but it also got the message to the air force command.



Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

zopi

Antiaircraft dumplings. That IS funny.

It always amused me...people buy houses in a flyway and the gripe about the noise...
Got Wood?
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Brucer

As I recall, she was there before the air force (and before jet engines). :D
Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

zopi

That happens too...it would suck to found an engine at full burn...

Still...that would take some skill...lol...edible flak...
Got Wood?
LT-15G GO chassis added.
WM sharpener and setter
And lots of junk.

jueston

I have a vague memory of a tv show about people who build trebuchet for some kind of competition and the lead guy said something like most people build their first one out of pine and very quickly find out that you need more strength then that will be able to give you, and that most of the ones in the competition were made of oak.

I can't promise that is accurate, it's just a half remembered quote from an unknown person....

zopi

somewhere on the web, I had found a guy who built a full size working ballista...which would chuck a spear or a tennis ball sized ball of concrete like four hundred yards...
Got Wood?
LT-15G GO chassis added.
WM sharpener and setter
And lots of junk.

zopi

Got Wood?
LT-15G GO chassis added.
WM sharpener and setter
And lots of junk.

Rooster

"We talk about creating millions of "shovel ready" jobs, for a society that doesn't really encourage anybody to pick up a shovel." 
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losttheplot

DON'T BELIEVE EVERYTHING YOU THINK !

Okrafarmer

Maybe hickory or locust. Oak if you can't get them. If you have to use pine, in your area, I would look for red pine.
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