the 40cm trebuchet project

[JodyH]

Damn you Freshman science, you just cost me 4 hours and about $75 to build a max 40cm x 40cm x 40cm trebuchet to launch a tennis ball into a 1m target at 5m, again at 7m and again at 10m.
I spent 4 hours with my boy perfecting a gravity only powered trebuchet THEN he tells me we could have used freaking bungee cords....
Fuck me dead... that would have greatly simplified shit 3 hours and $50 ago.

That is all
:p

[Lon]

Damn you Freshman science, you just cost me 4 hours and about $75 to build a max 40cm x 40cm x 40cm trebuchet to launch a tennis ball into a 1m target at 5m, again at 7m and again at 10m.
I spent 4 hours with my boy perfecting a gravity only powered trebuchet THEN he tells me we could have used freaking bungee cords....
Fuck me dead... that would have greatly simplified shit 3 hours and $50 ago.

That is all
:p

Awesome. Hope they do that in my daughters class.

[JodyH]

3:1, sling attachment point to pivot : pivot to counterweight attachment
1:1, sling length : sling attachment point to pivot
100:1, counterweight : projectile weight
Those are the ratios you'll be starting with.
Good luck and prepare to make 6 trips back and forth to the lumber yard even with a well stocked garage and scrap pile.

[Lon]

3:1, sling attachment point to pivot : pivot to counterweight attachment
1:1, sling length : sling attachment point to pivot
100:1, counterweight : projectile weight
Those are the ratios you'll be starting with.
Good luck and prepare to make 6 trips back and forth to the lumber yard even with a well stocked garage and scrap pile.

Thanks!!!

[mmc45414]

I still love my buddy's rig. He made it to break down so it could live in the garage until Halloween when he would set it up to throw the pumpkins into the woods. Made a swing seat and used a couple kids as the counter weight.

[Bigghoss]

Get it to fling a tennis ball 30+ meters and sell them to dog owners. That would be the coolest way ever to play fetch with your dog.

[gtae07]

Damn you Freshman science, you just cost me 4 hours and about $75 to build a max 40cm x 40cm x 40cm trebuchet to launch a tennis ball into a 1m target at 5m, again at 7m and again at 10m.
I spent 4 hours with my boy perfecting a gravity only powered trebuchet THEN he tells me we could have used freaking bungee cords....
Fuck me dead... that would have greatly simplified shit 3 hours and $50 ago.

But at least you built a real trebuchet, and not a catapult...

When my son is old enough we're building one. I've also harbored a dream of a pintle-mounted crossbow for the bed of my truck...

[RoyGBiv]

We finished a potential - - > kinetic energy car last weekend.
1.5M(height)x.5Mx.5M max.
Had to cover 5M including a small incline.

About $40 and 7-8 hours invested. Worth every bit when I got the text message in all caps.. "PERFECT SCORE!"

(Although I'm jealous over the Trebuchet project)

[Artemas2]

This book was essential in my parents raising of me
https://www.amazon.com/Backyard-Ballistics-Cannons-Cincinnati-Dynamite/dp/1613740646/ref=sr_1_1?ie=UTF8&qid=1512735685&sr=8-1&keywords=backyard+ballistics
(hopefully i linked that correctly for P-f dollars)

[STI]

Not real without pics.

[Peally]

Make sure to put old grapes and such in it so they rot after being shot and end the siege quicker.

[Sal Picante]

Not real without pics.

^^^ THIS!

C'mon... I've got a daughter that is going to "science this shit out" one day... Need help!

[Sal Picante]

Make sure to put old grapes and such in it so they rot after being shot and end the siege quicker.

The equivalent of hurling plague victims over the battlements?

[STI]

When I was in Scouting we came up with the idea of going to the grocery stores and pumpkin patches the day after Halloween and asking them if they wanted help "taking care" of the leftovers, filling up pickup beds with half rotten free pumpkins. The following weekend we held a pumpkin launching contest. Entries could be trebuchets or slingshots. The contest was held in a horse pasture which was about 3/4 acre square.

The first year the best trebuchet shot about 50 yards.

I think year 3 was when the pumpkins went into low earth orbit and started landing in the neighbors yard, and the contest didn't run after that.

[JodyH]

Pics when it returns from assaulting the gym ramparts this afternoon.

[Robinson]

I helped my granddaughter build a working solar cooker this year for science class and that was sort of fun. It doesn't reach nearly the coolness of a trebuchet. Not even.

[Shotgun]

How did you design the pouch so that it would let go of the projectile at the right time?

[JodyH]

How did you design the pouch so that it would let go of the projectile at the right time?
It's just a matter of tweaking the angle of the finger that the pouch cord loop slips over.

[JodyH]

BTW: the project sheet had a omission that fucked us (and many others). I'm going to email the teacher about it.

They specified the target size = 1m x 1m
They specified the target distance = 5m, 7m and 10m
They didn't specify that the target would be vertical on a wall and 1m up from the floor.
Without that being specified we went on the assumption that horizontal distance was the key element of the challenge and built our trajectory around hitting a 1m x 1m target either laying flat starting at the designated horizontal distance or a 1m x 1m vertical target at floor height at the designated horizontal distance.
Not specifying vertical target displacement and then placing it 1m off the floor is a pretty big fucking deal when it comes to tuning a trebuchet.
A lot of the trajectory is permanently tuned in with the sling release point and can only be slightly altered via more velocity.
It basically releases at the same angle every time and the velocity only changes how far it travels at that angle before dropping.

Im pissed.
LOL

[Peally]

You've failed the siege. Rebuild another Warwolf and try again in 6 months when it warms up :D

[Shotgun]

BTW: the project sheet had a omission that fucked us (and many others). I'm going to email the teacher about it.

They specified the target size = 1m x 1m
They specified the target distance = 5m, 7m and 10m
They didn't specify that the target would be vertical on a wall and 1m up from the floor.
Without that being specified we went on the assumption that horizontal distance was the key element of the challenge and built our trajectory around hitting a 1m x 1m target either laying flat starting at the designated horizontal distance or a 1m x 1m vertical target at floor height at the designated horizontal distance.

I'm no math whiz, but that sounds like at least a 10% to 20% variance at the distances quoted. Good reason to be a little pissed. If you were trying to breach the walls of a castle, you could just move your trebuchet forward or back as needed to get on target (as long as you stayed out of arrow range). Sick "Sam" on the teacher for the omission. https://www.youtube.com/watch?v=tgj3nZWtOfA

[JodyH]

We could have easily tuned it to hit the target with more velocity, but since the project sheet said nothing about vertical displacement we didn't worry about it.
Since nothing on the sheet had anything to do with height except the target size was 1m square we tuned everything around hitting a 1m cube at 10m distance and fine tuning the shorter distances via subtracting weight.
Using gravity alone to launch a tennis ball 10m requires close to 12# of counterweight on a 40cm long throwing arm w/sling, that's a shit load of stress slamming down on a trebuchet that size.

I'm still pissed.
By God this was MY project!

LOL

[Shotgun]

By God this was MY project!

Of course it was! Just about anyone who has ever been a parent knows that. I hope you get an "A."

You were probably typing a response as the time I edited my previous. You might have missed the link to the Killer Rabbit of Caerbannog. I often think of that rabbit when I see your avatar.

[Lon]

This thread really does need pics and video.

Just sayin’.

[JodyH]

Trebuchet is currently in the "impound yard" at the science lab until we get this all sorted out with the teacher on Monday.