# "The Insensible" - a counterweight trebuchet

10 Steps
Lindsey over the road has a big back yard. My family as been coveting his land for some time now. Finally I decided enough is enough, and began to plot the annexation of number 5. The first hurdle to overcome was getting past the formidable defences - a 6-foot high wooden fence with reinforced gate. Thus I began to design a weapon capable of reducing them to rubble. The "Insensible" is a 5.85m* high counterweight trebuchet including an added 2m of sling.

Note: I've written this instructible in the first person, because it is far from an authoritative set of instructions, but merely an account of how we went about building a trebuchet, compiled to help others create their own.
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## Step 1: Theory

The trebuchet is a siege engine that was employed in the Middle Ages, both by the Muslims and the Christians, and did not become obsolete until the 13th century - well after the intruduction of gunpowder.

The trebuchet consists of a base and a swinging arm. On one end of the arm (the much longer end, to gain mechanical advantage) is a sling in which the projectile to be fired is loaded. On the other end is a heavy counterweight.

The sling is a very clever edition to the trebuchet. It acts as an extention to the arm, without the added bulk of extra timber. When ready to fire, the sling is attached at both ends to the arm, but as the arm swings around, one end of the sling detaches (when it detaches is adjustable, to account for differently weighted missiles) and opens out to allow the projectile to be thrown free.

Most of the "Insensible" is made of recycled wood, with a steel crossbar (the axle for the arm), and concrete counterweight - 120kg.
MegaNerd says: Jul 5, 2012. 2:01 PM
How big does the axle and the 2 other bars have to be? (Thanks a lot for this instructables it was very useful and awesome) :)
Live long and prosper.
squiggy2 (author) in reply to MegaNerdJul 5, 2012. 6:52 PM
The axle we have is about 3cm diameter and we used the same bar for the counterweight pins. Originally it was a hollow tube but that bent on the first use. We couldn't find 3cm solid bar anywhere so we ended up putting a number of consecutively smaller tubes inside each other to make a solid bar.
Thanks for the compliment and well wishes!
laxap says: May 19, 2012. 1:27 PM
"...one end of the sling detaches (when it detaches is adjustable, to account for differently weighted missiles) and opens out to allow the projectile to be thrown free."

Can you please explain how it works?

I'm making a trebuchet, and my fear is the the projectile does not free itself and stays tangled into the sling.

squiggy2 (author) in reply to laxapMay 19, 2012. 4:08 PM
--setup--
- one end of the sling is attached to the arm of the trebuchet, and the other to hangs free and is attached to a ring.
- In step 9 you see the the release mechanism. It's pin, an you can adjust its angle with respect to the arm. The ring goes over this pin, so that the sling is now attached to the arm at both ends and the projectile won't fall out

--firing--
- When the arm rotates around, the sling moves with it, but at a higher speed.
- As the two bodies (arm and sling) rotate, due to their different velocities, the angle between them will change. In the beginning, when the arm is at rest, they're at ~120° to each other.
- Thanks to centrifugal force, as the sling rotates around, the projectile imparts a force on the sling outwards at 90° to its direction of motion like swinging a bucket round an the water stays in.
- When the sling moves to be roughly inline with the arm, at 0°, the projectile's centrifugal force will be acting at ~0° to the arm too, and it pulls the ring off the pin.

- What keeps the ring on the pin is friction. The projectile is always trying to pull the ring off, with its F*cos(a) where F is the centrifugal force and a is the angle between the sling and the pin.
- at 90°, the cos(90) is 0. So it is physically impossible to pull the ring off.
- at 1°, it would never happen, but if theoretically you had a ridiculously heavy weight moving extremely quickly, F*cos(1) would be enough to overcome the friction between ring and pin.
- at 0°, cos(o) = 1, so ALL the centrifugal force is acting to pull the ring off the pin

- SOOOO, the heavier the projectile, the earlier it will release, because it will have more centrifugal force to overcome friction at larger angles. This means that you have to adjust the angle of the pin so that is points more upwards (when arm is ready to fire) so that when the sling releases at 0° to the arm, not earlier.

There's a good video here showing a slow mo of the sling releasing if you need a visual
squiggy2 (author) in reply to squiggy2May 19, 2012. 4:11 PM
*edit: I meant at 89Â° it would never happen, not 1Â°.
At 1Â° it would almost certainly release with anything weighing more than about 1 gram (the weight of the empty sling would be enough)
laxap in reply to squiggy2May 21, 2012. 12:06 PM
jldiguiseppi says: May 17, 2012. 1:34 PM
we made a trebuchet for a scout project. We lobbed water balloons into the campsite of another troop, to our great amusement.
The best projectile was to tape sparklers onto softballs. DIY meteors; very cool
rogiewan says: Feb 13, 2012. 9:25 AM
Hey now this is EXACTLY what we need over here in Ireland! Maybe a tad BIGGER though. Thanks for the instructions and helping me to realize that I am not alone in my madness and that stuff NEEDS to get launched! Amen
nehi says: Aug 14, 2011. 2:11 PM
I take it you play rome total war. Awesome !!
itri45 says: Jul 17, 2011. 7:03 PM
good job with the trebuchet. few changes and suggestions first off all trebuchets use counter weights. second i would hinge the counterweight in between the main axle and itself creating greater efficiency. next try a more advancd design like a floating axle trebuchet or king arthur trebuchet or my favorite the floating axle king arthur trebuchet (FAKA).
good work
squiggy2 (author) in reply to itri45Jul 17, 2011. 8:33 PM
Thanks for the suggestions!
I've been thinking about a floating arm trebuchet for a while now, but I'd never heard of a King Arthur - I just googled it and am very excited :P
itri45 in reply to squiggy2Jul 19, 2011. 5:09 AM
yes, the king arthur is a little more advanced especially with the trigger release system. i am proobaably going to make an 'ible on the FAKA im building. great job.
oh and is the massive counterweight really necessary
squiggy2 (author) in reply to itri45Jul 19, 2011. 9:37 PM
No not at all, most of the time we're actually just running off 2 of 4 weights (so 60kg) but with a missile of any more than about 1.5kg there's a noticeable improvement in distance using the full 120. Also, I just came across an article on "traction trebuchets", which used teams of slaves and a big rope to pull the arm around, so there :P
itri45 in reply to squiggy2Jul 20, 2011. 11:43 AM
I have never heard of a Traction Trebuchet. that sounds like a crazy idea. what is your regular ammo for your trebuchet, rocks, logs, or somethings else.
squiggy2 (author) in reply to itri45Jul 21, 2011. 5:30 AM
Yeah I guess so, the usual - boulders, dead cows etc.
actually it was the first kind of trebuchet, before they thought of using a big weight
itri45 in reply to squiggy2Jul 21, 2011. 10:01 AM
oh i also notice in the video that oyur throwing arm is curving during every throw. i would try and make the arm one peice as when the arm curves you lose energy due to the joint.
itri45 in reply to squiggy2Jul 21, 2011. 9:57 AM
i normally just throw rocks or waterballoons. once i tried to throw a firework. it didnt work too well. :)
traction trebuchet. hmmmm
just a crazy idea
splazem says: Jul 14, 2011. 6:56 AM
I've made a couple trebuchets in my time, but never one that was mobile! Great job!
squiggy2 (author) in reply to splazemJul 17, 2011. 4:54 AM
Thanks very much!
I too have made a few catapults in the past, but when we designed this one we decided that it was one of the - if not THE - main criteria that it would pack up really easily and be fully transportable
splazem in reply to squiggy2Jul 17, 2011. 7:48 AM
Cool!
Kaptain Kool says: Jul 13, 2011. 4:09 PM
Okay, this is pretty cool, and the counterweight makes it look kinda like Thor's hammer or something!
LeonArchiTesla says: Jul 13, 2011. 11:50 AM