ballista plans

[baden]

Does anyone know where I can download plans for a ballista? We want to build one as a Pioneering project. Thanks.

[EagleInKY]

Google it. There are a bunch of plans online. I've never done it, but it looks like fun.

[baden]

I've found a few sketches on a couple of websites. Not much detail and no dimensions given. I can probably figure this out, but I am a huge fan of not re-inventing the wheel, so if anyone has a decent diagram of a ballista I would love to see it. This will free up my time for my normal duties such as filing tour permits, lining up drivers, nagging Patrol Leaders to give me a head count, rounding up health forms, and insuring 2-Deep Leadership.

[Crew21_Adv]

Baden and Fellow Scouters,

 

Greetings!

 

This page should be a good resource for all our Scouters. I cannot find instructions for a Ballista, but there is a good image on this site.

http://www.pioneeringprojects.org/index.htm

 

Crew21 Adv

[baden]

ZOWEE ! ! !

 

The plans for the Glenn Cockwell's catapult on this web-site is exactly what I need. I don't know the difference between a ballista and a catapult, but this is great. THANKS Crew21 Adv. You have done your good turn for today.

[fling1]

One of my favorite topics!! This might be a bit more ambitious than what you asked for, but I'll post it anyway in case others have perked up their antennae on this topic. I like to think of this as the world's only Cub Scout-powered trebuchet. I don't have a picture handy of the scouts playing with it, but here are some of my cow-orkers and neighbors giving it a try...

http://scouttroop.org/oh/bsa/476/kidsonbench.jpg

http://scouttroop.org/oh/bsa/476/wildride.jpg

http://scouttroop.org/oh/bsa/476/treblaunch.jpg

http://scouttroop.org/oh/bsa/476/mid-fling.jpg

and http://scouttroop.org/oh/bsa/476/punkin1.mpg

There are plenty of internet resources to help you design a trebuchet, if you want to get into this topic. If you poke around, youll see that it is pretty easy to get in deep :-) Heres some initial stuff to get you started

After a bunch of reading and looking, I settled on the following useful rules of thumb (all of which are observable in the photos I linked):

hinged counterweight

beam length ratio: 4:1 5:1 (I used a 16 2x6 with the axle at the 3 mark that makes 13:3)

axle height such that the cocked machine is at ~45 degrees

Sling length ~= L1 (longer of two arm lengths) this puts the ammo more or less right under the axle when cocked

Weight ratio = 40:1 50:1 (we throw 8 -10 lb pumpkins with ~450 - 600 lbs or so of people. We threw a bunch of 5 lb-ers this year and they launched beautifully with ~250 lbs of people. Voice of experience: if you get this ratio too low, you will release early and throw vertical not a good thing :-)

Release pin angle is pretty adjustable to get a well-timed release

You can get a more efficient machine by diligently working through the many variables. But you will get a working machine quickly with these rules of thumb.

I built mine in the pioneering tradition of trees and rope for several reasons:

cheap materials, easy to scale up

always enjoyed pioneering and thought this was a cool way to show scouts that it can be fun

tripod design means this can be built on uneven ground and made perfectly level!

This last point is really the best reason. Set up the tripods and install the axle. Take your time to adjust the legs so that the axle is level and perpendicular to the desired throw. Very small leg placement adjustments will dial it in nicely. When all is squared away, install the braces on the tripods.

Note that with 500 lbs, you are putting a large load on the tops of the tripods. Use stout timbers and strong rope. I buy a new 50 bag of 3/8 manila each time I assemble it, just for the tripod lashings. I have found significant rope stress, including breaking, when I disassemble it. I also try to keep the tripods as close together as I can, so that the axle takes less bending stress.

Hope this helps,

-Derek.

 

[SWScouter]

Yeah, I think building a catapult or a trebuchet is probably the way to go. Personally I don't think I'd want scouts building a very large crossbow. What would they use for bolts (big huge arrows)?