Trebuchet

If you want to pronounce it like a proper Southerner, I recommend starting with "Treeb-a-chett".

Anyway, I built a trebuchet over the past two weekends using plans from Issue 25 of Make.  Let's see how that worked out.

I started by getting the nice folks at Home Depot to cut up a 4x8' sheet of plywood according to the plan spec.  When I got them home, I laid out the base and attached the cross pieces to make it more rigid.

 

Next, we added hinges.  This is a fold-and-store trebuchet - it'll fit in your closet!

Next, I screwed together pieces of 2x6" board to make the uprights.  These need to be very sturdy, as they provide the fulcrum for the throwing arm.

The uprights are attached to the base with strap hinges - the hinges are not what holds them in place, though.  At the top of each upright, screw-eyes are inserted to act as anchor points for guy wires.

How to make a guy wire
Get a length of 1/8" galvanized wire rope.  Use matching wire clamps to make loops at each end.  When you mount the guy wire, put a turnbuckle at one end (I used 1/4" by 5" turnbuckles) to properly tension.  This is easiest if you read the preceding sentences and execute them backwards like a Tarantino movie.

What?  I mean fully extend your turnbuckle and use that length to measure how long your cable should be.  This means you'll have a few inches of give in tensioning.

Attach yer Flanges!
The uprights get flanges, and the counterpoise deck gets flanges.  Check underneath your chair.  You guy a flange!  Everybody gets a flange!

The end result of all that looks something like this.

Drill Yer Steel!
The throwing arm needs two holes, the cross needs a hole, and the end cap needs a hole.  Drag your drill press out of its corner.  If you don't have a drill press, don't try this at home.

Clearly the maid has been neglecting my drill press.

You'll bolt some screw eyes through these holes, and tension another guy wire along them.  I assume this helps keep the throwing arm from bending or breaking under stress - it's never properly explained.

Anyway, you'll also need a ring to hold down the throwing arm when preparing for launch.  Use a 2" hose clamp for this.

Now you're ready to attach the throwing arm and counterpoise deck.  If you've been following along closely, your trebuchet will look something like this.

Finally, you're ready to build the trigger mechanism.  I made a mistake here, in putting the chain mount in the center - this gets in the way of the stuff you're launching.  Mount it off center, preferably off on one of the side decks.

Also - my panic snap didn't want to release very easily, so we devised a two-part trigger.  On one side, someone pulls a nylon string to open the snap - this is the "safety".  The snap stays caught on its lip until a person standing on the other side gives a solid yank from the other direction to pull the snap off the ring.

So let's see how it worked in our test runs with tennis balls and about 60lb of counterweight.




and...


As you can see, we had a little bit of trouble with the counterweight on that last go-round.  I'll be switching to big ol' bags of cement next time.