Trebuchet complete

[johnridley]

well, mostly. Everything's built. I need to adjust some stuff, I need to buy some rope and make a sling, I need to buy some more hardware to really secure the weight box. The throwing arm needs to be trimmed and some hardware added.

I had these ridiculous ideas of having some people just pull down on the sling to get the thing ready to fire. WRONG. We dry fired it with no weight in the box, and it took three of us to pull it down, and I was nervous about that. I could hold it down myself without too much trouble, but it's awkward to pull down, and the whole time you're thinking "if someone lets go, this is going to tear up my hands and hurt me."

Luckily I did buy a winch for this project. I will need to find pulleys too. Lowes only has really crappy 200 pound pulleys that I put back on the shelf, I don't trust them. I don't think I'd even trust them with their rated weight.

Ah, I see Harbor Freight has decent-looking double-pulley blocks rated 300 pounds. One more reason for a trip there tomorrow.

Oh well, this wouldn't be a berzerker project if I just showed up with it ready to rock. There'll be plenty of participation with this project.

For your enjoyment...

Comments

[johnridley.livejournal.com]

Yeah, eyes of various types are on the shopping list for tomorrow.

I'd thought about making steel plates to reinforce the stress points, but I figure for the first year, we'll just fire the thing until something breaks, thereby determining empirically where the stress points are.

I am trying to decide whether to mount the winch or not. Harbor Freight has some double-2-inch pulleys. Even a single pulley up high giving a 2:1 gain would probably make it pretty easy to pull down. Going with a double at 3:1 or 4:1 is a possibility too and probably still faster than using the winch.

Right now the winch is loaded with steel cable, but I'm thinking I'll take it off and put nylon rope on it for this job, IF I use it.

I may buy some different lumber for the main mount of the weight box. That's two 4-foot pieces of 4x4. Problem is, when you pull the beam down the last 30 degrees or so, the box hits the beam and cocks back. I guess that's not horrible but it looks weird and I'm not sure I like it.

[erikvolson.livejournal.com]

Two double blocks with eyes. One eye to the beam, one eye to the base. You'll need an eye splice around one of the beam block sheaves, or use wire rope and d-clips (or a single block with two eyes)

That'll give you a 3-1 purchase. Two sets means two people hauling on would provide 600 pounds of downward force on the beam, each block holding 150lbs, each person pulling 50 lbs.