Jonathan's Trebuchet

In order for Jonathan to complete his engineering requirement for Cub Scouts, he needed to follow a blue print or build plan to construct an item of his choosing.  I looked around online to give him a few ideas and we came across the trebuchet, which I had never heard of.  We found a site that listed build plans so we decided to give it a shot.  We scaled our version down 50% to make it more manageable.  We used scraps around the house and Jonathan did much of the work (measuring, marking, cutting, drilling, hammering, etc.) as I provided instruction and assisted with the power tools.  It was a fun project that we continue to toy with as we work towards our end goal of launching a water balloon to hit the Wells' house :)

First step was to trim down a few pieces of PVC plank to the correct width.  He didn't operate the saw alone, I just stepped away to take the pic.

Next, we cut the pieces to length and angled a few of them as needed.

Screws would have been best, but I didn't have the correct size so we used extra nails I had around.

We measured and centered holes for the axle and Jonathan drilled them out.

Same for the launch arm.  One key factor was to have the long portion of the arm measure 3.75 times longer than the short portion.  With a 4' piece of wood, we determined the hole needed to be 10" from the end.

Jonathan drilled holes to screw in hooks for the safety / launch mechanism (an arrow).

At the end of the launch arm is a nail that controls the release angle of the payload.  I used the below image to show Jonathan how it works and how adjusting the forward/backward angle of the nail impacts the release angle.  The further forward the nail is, the later/lower the launch angle.  The angle will vary based on payload weight and counterweight.

We logged our launches to determine the average distance using different balls and counterweights.  Jonathan launched while Kaitlyn marked their landing.  We tested a wiffle ball, tennis ball and baseball and used counterweights of 5 lbs, 10 lbs, and 25 lbs.  Each ball was launched 3 times with the same weight to allow us to determine an average.  We found the 5 lbs counterweight was too light to launch any of the balls so we quickly moved on to 10 lbs.  A day or two later, Jonathan completed the math to determine the average distance for each, which are listed below:

                              10 lbs               25 lbs
Wiffle ball             13'8'                 29'5"
Tennis ball            21'5"                46'6"
Baseball                14'9"               35'5"

We launched the tennis ball with a 35 lbs weight and recorded the longest shot of 71'3".  Based on the known tennis ball distances above, we determined the average distance using 35 lbs should be 70'10".  This was really darn close to the actual distance so we felt good knowing our theory tracked right along with our testing.

Here's a video collage of the launches, some were successful and others...not so much.  Enjoy!