First Launch

First test today, went interestingly. We delayed until late at night, which turned out to be quite detrimental to the camera quality. Launch site was a baseball diamond, which turned out to be perfect with the backdrop and clear area in front. The pulley system of the webbing turned out to have  ridiculous amounts of friction and the the bridal holding up the arm when it is being cocked traveled down the arm, making it lie at a skew angle. The first throw was with 180 lbs of counterweight, and threw about 70 yards. The second throw hit a protruding bolt on the way down, and threw about 40 yards at a weird angle. Hoping to test it out again before E-days next weekend.

So close!

We made the vertical counterweight guides today, 2 pairs of 10 foot 2x6's which guide the counterweight axle as it falls. They are each fixed to the frame with 6 carriage bolts so they can be removed for transport. We also cut the CW axle, 48" long out of 1" hot-roll steel. To keep track of pin angles, we added a small scale to the end of the arm. It doesn't show the angle, but we just need repeatability.

Almost There!

Frame is almost done, just need to get the vertical guides and bolt them on. The arm just barely hits the ceiling of the shop when upright, so we wheeled the whole thing outside to get all the lateral supports on. These supports go between the diagonal members and keep the halves of each rail aligned. Fortunately, we were able to move them reasonably close to the center with the arm hitting them. They are circled in orange in the picture below:

We also worked on a little addition originating from the generic F3K Floating Arm design, by adding a small piece between each of the central vertical supports, which the counterweight axle hits at the very bottom of it's motion. This allows the wheels to "pole-vault" over the gap, reducing the stress on the frame and eliminating the quintessential "bump-bump" sound of the wheels hitting the forward rails. The video below shows my colleague demonstrating the wheels appearing to float over the gap due to this addition:
 

3rd Wheel and Trough

Pretty self-explainatory, really. Trough is just scrap ply, 3rd wheel supports are 2x4's in various orientations.

Frame Part 2

Remembered to snap some pictures this time. This is the alignment loss due to to the warping of the vertical 4x4's:

I also added in the upper gussets and the four diagonals. A little wedge action on each end allows for everything to fit nicely together. Also, the glue added on the wedge lubricates it, making it easier to tap in, then holds it in once it dries.

A week in and the frame is looking pretty good. The vertical supports are in and the rails are ready to put on. Unfortunately, the central vertical pieces have splayed outwards significantly, making the rails non-collinear. Hopefully, as we add on the gussets and diagonal pieces we can coerce them into alignment. The treb is now taking up a good deal of room in the shop, so we are keeping it on a cart so we can roll it around. Sorry about the bad pics, I keep forgetting about them until I have to leave for class.

Construction updates

We are currently cutting out all of the 4x4 to length, as well as drilling holes for the lagbolts and counterbores. Since we have don't have a chop saw or miter saw, we have refined out technique to cutting them with the hand saw, a little time consuming that, and then cutting it square with the bandsaw. The bandsaw has a 16" throat, so we have had to do this for all of our long pieces. We have some gussets all marked up and ready to cut, and are hoping to bust them out tomorrow and start assembly!

Sling

Worked on the sling today, not sure if I like the design yet, though. The larger green lines are 3/8" tied with anchor hitches on one ring and a cow hitch on the other. The small brown line is paracord, with constrictor knots for where it attaches to the inner two big ropes and buntline hitches on the outside. The paracord was added while the big lines where taped to a hardhat, which gives the whole thing a nice concave shape when folded over.

Throwing arm

Arm has progressed well so far. It consists a two piece vertical lamination of pine to create a 1.5x5.5" cross section (shown in the first photo), then has a 2x6 doubler (second photo) on each side between the wheels and the counterweight hole. Additionally, the last 6" of the center piece has been rotated to minimize the chance of splitting along the counterweight axle. To offset and provide support for the wheels, two pyramid-like supports have been added, as well.  Both of these are visible in the third photograph.

So it begins...

Alright, here is the deal. I'm a student at Colorado School of Mines, where we have an annual engineering fest called E-Days. It's filled with all sort of quirky competitions, one of which it the trebuchet contest. Unlike many others, this contest is for accuracy rather than distance, trying to hit little castles at various distances. No size or counterweight restrictions, but you must throw a full gallon of water as a projectile. It is currently spring break, over which I have built the arm, leaving two weeks and some days to build the frame and test. Good news is, my colleague and I have already designed every part of the trebuchet in solidworks, with the exception of the counterweight buckets. Unable to locate any weight plates in significant enough numbers, we were planning on using large buckets with concrete. Now, let the fun begin....