New to the Hurling Bug

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New to the Hurling Bug

Postby JimL » Sat Jun 28, 2014 11:57 pm

It's in the administrative for some reason?
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Re: I posted in the wrong spot?

Postby JimL » Sat Jun 28, 2014 11:59 pm

New to the Hurling Bug

Postby JimL » Sat Jun 28, 2014 10:27 pm
It all started just before Easter when I decided to make a Floating Arm Trebuchet to launch Easter eggs. I am not an engineer or a carpenter so needless to say my eager task was not completed in time. I did complete the frame and sling arm and it functions very good. In a matter of understanding sling and release mechanics I made a "stave sling" or stick sling. I quickly realized that was all I needed to launch my Easter eggs. We were hurling baseballs, lacrosse balls and tennis balls 200 feet and beyond with them. At this point I employed the assistance of one of the most intelligent engineers in my industry to help design a large scale FAT to chunk pumpkins. My desires are somewhat simple in comparison to the extreme distances that can be achieved. I wish to hurl an 8-10 pound pumpkin 300 to 450 feet. I really would wish to have a completed trebuchet operating by the beginning of October and worry that the engineer will not have my design ready in time for fabrication before that point due to his busy schedule. So I was thinking of getting a standard counterbalance trebuchet made in time for this years season. My desires are to use aluminum 3"x5" square due to the rust resistance. But I am not opposed to using steel I-beams to cut cost? I plan on using a 12 foot trailer to transport the trebuchet and act as the base support via leveling legs. Beyond that I need lots of help, maybe simple help to folks that know the specifics to hurling objects 300-450 feet. First question is can it be done within the scope I discussed? Second is how long will the sling arm need to be? And last is, how much counterweight will be needed to propel an 8-10 pound pumpkin 300-450 feet? I thank you in advance for any help you can give. Thanks Jim

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Re: I posted in the wrong spot?

Postby madmattd » Sun Jun 29, 2014 11:37 am

Jim, Welcome to the Hurling Forums!

No worries on the mis-post. I'll nix the one in the Administrative Section since you re-posted it here and we can keep responses in one spot for you.

To answer your questions, sure it sounds doable. Since you are mounting to a trailer, your height is only constrained by any bridges you need to go under (and keep it under 13' 6" road height to stay legal regardless). You'll want to dis-mount the throwing arm when traveling so keep in mind a way to do that. So an 8-10' high main pivot (from the trailer deck) will be optimal use of your space to shoot a pumpkin.

Standard hinged counterweight trebuchets (HCWs) like you are looking to do usually use roughly 100x the projectile weight for counterweight, so up to ~1000 pounds in your case. That's a lot of weight, but not crazy given the size of materials you are looking to make your frame from. That ought to get you well out past your goal, less weight will shoot shorter, but likely will still get you out to 500 feet after much tuning work. Less weight is easier to cock (I highly advise a winch or ratchet or similar for this!) Steel or aluminum frame, the choice is up to you, but at least the arm I would suggest aluminum to keep it light (it needs to turn as fast as possible). I personally find steel easier to weld than aluminum, and it grinds better, but if you have experience with both than just go with whatever you prefer. Steel can be painted to minimize rust issues.

The most important part will be to keep your axles' lengths to a minimum, especially the main pivot. Braces extending inside the frame to support the axle just to either side of the arm will help greatly in this.

You'll want an arm ratio (long side to short side) in the 4:1 - 5:1 range, and the arm should be long enough that the tip of the arm when cocked is practically on the ground (or trailer base) and forms a 45-50 degree angle with the ground. Simple trig will help you out there with the exact sizes. As a starting point, the sling should be about 75% of the length of the long side of the arm, the exact length will need to be tweaked as you tune but that's a fair starting point given the parameters I've spelled out above.

Slinged Treb Still.png
Slinged Treb Still.png (9.02 KiB) Viewed 4414 times


We can get to tuning once you've got it built should you want some help there.

More questions? Just ask! Some more folks will pop up to help you out too. Post pictures as you build, we love pictures!
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Re: New to the Hurling Bug

Postby JimL » Sun Jun 14, 2015 12:28 pm

Okay now I have a new mission. Instead of a HCT that will be a metal frame and sling 500' I am thinking of a HCT that is a wood frame that will sling 300'. This thought is not to be trailer mounted but instead held together by metal brackets, to assemble as needed. If to use the specs of a 10' tall structure and using 6 x 6 treated lumber can this be done? How much counterweight should I look at using for my goal and will the 6 x 6 lumber hold up? Or should I up size to 8 x 8 lumber? Thanks in advance for any responses I may get.
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Re: New to the Hurling Bug

Postby TommyL » Mon Jun 15, 2015 5:33 pm

If you really want a FAT or F2K, build that! Don't wait for your engineer, build one to throw baseballs in an weekend and use that knowledge to build a pumpkin size version. Better to spend all your energy (and money) building what you really want instead of something to occupy your time. If you need pictures of a baseball version, I have them.

If you really want to build a HCT, 6x6 will be fine. The key is to minimize the distance your axle (the thing your arm hinges on) has to span. As far as counter-weight, you could probably get away with 500-700 pounds.
If my wife only knew how much money I have spent to throw fruit in a field...
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Re: New to the Hurling Bug

Postby madmattd » Wed Jun 17, 2015 8:10 am

6x6 will definitely be more than enough for what you are doing. Heck, we built Medieval Postal Service out of home improvement store 2x4s (tripled up in most cases) and that was way more than strong enough, and threw 9-pounders 1000-1300 feet.

Image

Like Tommy said, just keep the axle span short. Brace the axle, keep a narrow counterweight (and thus a narrow separation between the 2 frames), just do whatever you need to do to keep that thing from bending.

One rough idea for axle supports:
Image
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