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New trebuchet (Read 1032 times)

HurlinThom

Interfector Viris Spurii

Leverage artillerist

Posts: 1390

New trebuchet
Jun 23^rd, 2011, 11:52am

Built a half-size prototype of one I intend to enter in this Fall's pumpkin event at Cal State Fullerton. Finished the frame yesterday, fitted it with an existing arm, sling, and counterweight to test for function. Here's a still from the video I shot. Performance was not great, but the working parts were pretty mismatched.

If the wood seems assorted, it is. I used a bunch of boards that had been sitting around taking up space, some out in the weather.

MVI_2064.jpg

When all is said and done more will have been said than done.

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Bill Skinner Slinging.org Moderator Forum Moderator Slinging Rocks! Posts: 1363	Re: New trebuchet Reply #1 - Jun 23^rd, 2011, 8:35pm Looks like a neat job to me. Do the neighbors ever complain? Bill
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HurlinThom

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Posts: 1390

Re: New trebuchet
Reply #2 - Jun 23^rd, 2011, 10:49pm

Thanks. Bill. All angles and lengths were calculated pretty carefully, and cut as precisely as I could. I'm trying to make this one as close to half the big one as I can, within the bounds of practicality. This one is for practice, to make sure the calculations are valid. I really don't want unpleasant surprises when I get the 2X6s I actually paid for cut.

No neighbor complaints, but they're mostly pretty cool. I limit myself to tennis balls so no real damage gets done.

BTW, I made a couple of minor changes and increased throwing distance around 40%.

When all is said and done more will have been said than done.

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Masiakasaurus Slinging.org Moderator mah-SEE-a-kah-SOR-us Posts: 4944 Gender:	Re: New trebuchet Reply #3 - Jun 24^th, 2011, 10:31am Quote from HurlinThom on Jun 23^rd, 2011, 10:49pm: BTW, I made a couple of minor changes and increased throwing distance around 40%. What were the before and after distances?
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HurlinThom

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Posts: 1390

Re: New trebuchet
Reply #4 - Jun 24^th, 2011, 10:52am

Guesstimated 80 feet to indirectly paced-off 115. Wink

First shot hit my roof short of the ridge, second one was recovered in the jasmine ground cover in the front yard. The greater distance might have been impeded by a small tree, but bounce and roll are unlikely. Both release angle and velocity were visibly better on the later throws.

Might not sound like much distance but the frame is barely over 2 1/2 feet tall, and nothing "trick" has been tried yet.

When all is said and done more will have been said than done.

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Bill Skinner Slinging.org Moderator Forum Moderator Slinging Rocks! Posts: 1363	Re: New trebuchet Reply #5 - Jun 24^th, 2011, 12:00pm Where do you go to test fire? If your treb is like a sling, your ammo limits your range, which can be a good thing, but don't you really want to know what it is capable of doing? Bill
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HurlinThom

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Posts: 1390

Re: New trebuchet
Reply #6 - Jun 24^th, 2011, 12:19pm

Well, there's a park I go to, but I have to wait until the off-leash dogs clear out. Legally the dogs ought to be on-leash, but that's ignored. Since most of my trebs are small I can use the back yard for early development. I have around 130 feet to play with before things exit my yard. The better efforts do wind up on the lawn across the street. I may have hit that house on occasion, but tennis balls have almost no energy left after traveling that far. As I find more ways to increase performance I build smaller to avoid problems/confrontations.

Just stuck a video up on YouTube, for those who are interested.

http://www.youtube.com/watch?v=LP5yq45nO_A

When all is said and done more will have been said than done.

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curious_aardvark Slinging.org Administrator Taller than the average Dwarf Posts: 9049 Gender:	Re: New trebuchet Reply #7 - Jun 24^th, 2011, 1:13pm Quote: but I have to wait until the off-leash dogs clear out. lol you miss a trick there - just get the dogs to bring the balls back like the video too. So what weight you got on that ?
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Morphy Interfector Viris Spurii Checkmate Posts: 2432	Re: New trebuchet Reply #8 - Jun 24^th, 2011, 5:16pm Maybe I'm looking too far into this but it seems like the treb's arm in the picture is about the same length as the sling portion? Is that correct and is there a certain golden ratio that lets you know the most efficient length for each in proportion to one another?
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HurlinThom

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Leverage artillerist

Posts: 1390

Re: New trebuchet
Reply #9 - Jun 24^th, 2011, 6:10pm

Morphy, the golden ratio is whatever works best. In other words it's situational. If the arm is fast (light, low moment of inertia, light projectile, or heavy counterweight) it sling needs to be shorter. And a longer sling goes with a slower arm. You're trying to get sling release at the point where as much of the energy as possible has transferred from the falling counterweight into the ball. There's some disagreement as to the particulars, and it's likely really a boring subject unless you're actually trying to optimize a treb's tuning.

CA, that's 20 pounds (iron, not Stirling). About 9 kg to those in the modern world. Plus a couple for the attaching gubbins. Matsu isn't much of a tennis ball chaser. Can't be bothered with piddly little stuff like that. As a youngster she did try to catch a Saluki, pretty amazing; they circled the park a few times until the Saluki kicked in the afterburners and left her. That's supposed to be the fastest breed in the world.

Ah, you meant the dogs in the park. Dog slobber all over my nice tennis balls? I think not. Plus they'd "fetch" the balls to their owners, not to me.

When all is said and done more will have been said than done.

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Masiakasaurus Slinging.org Moderator mah-SEE-a-kah-SOR-us Posts: 4944 Gender:	Weapon of Medi(a)eval destruction Reply #10 - Jul 26^th, 2012, 12:54pm Off topic replies have been moved to This Thread
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ChuckRocks Descens Leverage Artillery Design Engineer Posts: 290 Gender:	Re: New trebuchet Reply #11 - Jul 29^th, 2012, 9:06am Quote from HurlinThom on Jun 23^rd, 2011, 10:49pm: No neighbor complaints, but they're mostly pretty cool. I limit myself to tennis balls so no real damage gets done. They don't dare. They all think he's one of the Capitol One Vikings.
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xxkid123 Past Moderator Hallo, ich heiße kartoffel Posts: 4798 Gender:	Re: New trebuchet Reply #12 - Jul 31^st, 2012, 6:40pm Quote from ChuckRocks on Jul 29^th, 2012, 9:06am: Quote from HurlinThom on Jun 23^rd, 2011, 10:49pm: No neighbor complaints, but they're mostly pretty cool. I limit myself to tennis balls so no real damage gets done. They don't dare. They all think he's one of the Capitol One Vikings.
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HurlinThom Interfector Viris Spurii Leverage artillerist Posts: 1390	Re: New trebuchet Reply #13 - Oct 20^th, 2012, 2:48pm Little update on the small one. I just finished a very light arm (using up some materials that were taking up space in the shop) and put a small video of an ealy shot up on You Tube. http://youtu.be/diml-21PIY0
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