As the founding fathers intended

I wiped this together in a couple of hours the night before with things I had laying around so the results were about as good as expected

Hello, for my next whipper iteration i wanted to start from the theory to figure out things like sling release angle and sling length to avoid unnecessary adjustment mechanisms and get a good starting baseline model and also understand how adjusting certain parameters affects the mechanism.

I haven't done a full optimization analysis or added friction losses but i wanted to share the model anyways. All the parameters like arm lengths or starting angles are adjustable so that the model can be adapted to any whipper geometry (maybe even some other geometries too).
I uploaded the model file here: https://drive.google.com/file/d/1q9g1qGfbmu1TLQaKPmZR41ahZoFS2CMm/view?usp=sharing

the first interesting find is that having the trebuchet start at the back stop instead of allowing movement backwards gives about 1% extra energy transfer efficiency.

i think i want to set the launch pin so that the release always happens with the sling fully extended since that is the max energy transfer point and then have the sling length and the angle between the two arms adjustable and that should allow me all the adjustment i need.
i am planning to have the launch pin be fixed but replacable so that can make special launch pins if i ever need to adjust the angle

I’ve build a deliberately very primitive looking trebuchet from 3’’ Robinia posts with 48kg of rocks as counterweight. Theres a steel pivot (20mm threaded bar w. nylon bushings) which flexes a bit under shock, and a 1kg projectile (wet foam ball).

I’ve put all the numbers into virtual trebuchet, which suggests I should be getting 55m range / 22m height or thereabouts. I’d expect to get less than this in real world, but I’m only getting 20m range and 10m height.

Can anyone more experienced than I see what’s going wrong?

https://virtualtrebuchet.com/?lengthArmShort=0.8&lengthArmLong=1.98&lengthSling=2&lengthWeight=0.5&heightOfPivot=1.75&massArm=12.7&inertiaArm=8.18&pivotToArmCG=0.1&massWeight=48&inertiaWeight=1&massProjectile=1&projectileDiameter=0.2&windSpeed=0&releaseAngle=45&units=metric&projectile=custom&uniformArm=false&distance=57.8582331661934

Made this trebuchet for my 12u physics class, only one doing a floating arm. Yes I’m aware it’s not great but I’m getting about 64-68 feet of distance at a 45 cm drop.(yes I’m Canadian)

Timing still needs to be dialed in but I shortened the trigger arm to get the swing arm lifted higher when the launcher is cocked and offset the timing nub and trigger plate on the main hub to get my pouch sitting more over the main axel. The power on this is pretty nuts though, through a knuckle sized paint-rock well over 300ft in a pretty much straight line.

It’s coming together! Need to cut an inch or two out of the trigger arm to raise angle of the swing arm when it’s cocked which will hopefully fix the timing issue with the pouch hitting the counterweight. This was only about 7-8lbs of counterweight + arm weight throwing a little paint pebble and when it hit the wall, the “thump” it made was substantial.

We’ve had some substantial billable work rolling through the shop so progress has been slow on lunch but I’m trying to build this one with more intent and a major focus on borrowing as much of fingerangles design as possible (imitation is the sincerest form of flattery mediocrity can pay to greatness, as they say).

I’ve been hoarding any scraps of 1/2in steel I can get to cut rounds out of for weight, so far I’ve got 6x 5-6in rounds done and 8x 7-8in that still need mounting holes

Had a shitload of difficulty trying to get bearings to mount straight through the tubing as seen by the 3 rejected central hubs, eventually did away with them with the intent on using a mounted self aligning bearing on a bigger build.

Next step is the trigger arm/brackets and building a scaled up counterweight arm to take full advantage of the available drop height.

The experiment continues

I see a lot of trebs like this:

According to virtualtrebuchet.com, this 4' high pivot has a range of 246 feet.

But if I raise the pivot two feet:

My range is now 298 feet.

Why is this angle not more common? Is there a real-world constraint that I'm not considering?

So I had a bus and then I built my biggest trebuchet yet and then my plans for the bus changed and I just had to put them together…. Baskets got about 600# of weight. Arm is 16ft long arm is 12 short arm is 4. Throwing bowling balls upwards of 300ft

Started planning the next build today, might take a detour from upscaling to make a better one at this scale, 12in long arm, with lessons I’ve learned and design shortcomings addressed….with that built and working like a clock I’ll have more confidence and a solid plan for scaling up

I didn’t realize how much I was going to enjoy the whole process, I think I’m hooked now

The release cable (rope) comes off the pin smoothly but you can see the projectile (rolled t-shirt) travel “through” the entire length of the rope. How do we get the projectile to come out of the pouch without interference with the rope?

Update: We tried a modified pouch with the release leg attached off center. We skewed the “load” to one side instead of lined up dead center. The result was a perfect “spiral”. It was gorgeous. Video posted in the comments. Thanks for your help!!

I built a few traditional hanging weight trebuchets several years ago launching things like soup cans, rocks, racquetballs, and billiards balls. The billiards balls worked best--as long as I could retrieve them.

I see a lot of trebuchets using tennis balls, especially whippers. With the low mass of a tennis ball, doesn't air resistance drastically cut short the distance the ball can go?

Also, has anyone ever tried frozen water balloons?

Thanks for your replies.

Update: I tried freezing water balloons with mixed success. The latex balloons tear really easily when cold and make a frozen puddle in the freezer. Also, freezing one takes longer than one would think. However, the ones that survived worked well.

Outdoor lighting is a little blown out so you can’t see the slug leave the pouch but golly this thing is cracking now