I'm going to build a trebuchet.

Dave Shepard · January 12, 2008, 11:24:19 PM

A hinged counterweight is as good or better than wheels. The size this one is going to be, wheels aren't an option. I have my drafting table setup, so I am going to try and scale up a drawing for it. Unfortunately the logging job I was going to get the trees from is postponed, possibly cancelled. The woman I was going to do the work for was ill before Christmas, and her daughter transferred the land into a trust, and is not in favor of logging. :( Just a temporary hurdle.

Dave

ljmathias · January 13, 2008, 06:35:14 AM

Neat posts! You all might be interested in Educational Innovations at www.teachersource.com. They offer several trebuchet kits plus the Nova video on two that were made in Scotland- lots of good information on the video and the kits allow you to experiment. My oldest grandson and I are building a rolling version but it can also be set up stationary. The video did a somewhat-scientific comparison of fixed weight vs hanging basket weight versions and concluded that the latter were better based on ability to change the weight in the basket and thus change the range easily. On the other hand, with wheels, you can easily change your impact target and also transport the trebuchet for attack at another location. Seems like a trade-off to me. One thing that was clear, though, was that pounding a castle wall with 250 lb sandstone balls is devastating and over a few days can reduce a wall to rubble.

One thing to be aware of with a big one: unless you have a pretty good idea what you're doing based on engineering and/or trial and error with smaller versions, there is a very real possibility of the ammunition going straight up and straight down: oops!

Have fun but be careful- big pieces of wood break things when the fall down or over...

Lj

shinnlinger · January 13, 2008, 09:48:57 PM

Dave,

I used to teach an applied physics class and we broke the video you saw down many many times. there is a great graph in it, but they only flash it and dont explain it. I believe it shows the ratio for the pivot point on the fulcrum was 5 to 1 and I oversaw at least 30 mini trebs in action. We built ours out of knex and hurled herseys kisses, but one of them only 5 inches or so could shoot the kiss over 30 ft and break a "castle wall" I assembled for scoring.

We found the best models had swinging counterweights that were 80 x the weight of the projectile. More than that was counterproductive and less didn't go as far. I beleive 50x is what the shoot for in the video. It is this weight that can be the trouble. If it is not at least 40x it can shoot straight up or backwards. The sling hook has to be just right also(the kids would bend this and dial the machines in), but the weight is the key. I heard Cortez built one when he ran out of powder against the aztecs, but he didn't put enough weight in it and the projectile went straight up and crushed the machine.

The toughest part was the sling (lenght and realease angle of the hook)and the kids would ussually settle for taping string to the kiss. Triggers could be troublsome also, but I saw some pretty good ones.

Interestingly, Ed Levin, the TFer in charge of the second swinging counterweight one lives not to far from here and I used to work in his shop albeit not for him. If you want I will try to contact him for plans to the second one if you are interested.

Dave Shepard · January 13, 2008, 11:33:13 PM

If you want to stir Ed a little, that would be great. I contacted him when I started this thread. He said he would see if he could get permission for the plans. I haven't heard from him since. I am sure he is too busy to put much effort into a "crazy" idea like this. ;) Oh, wait, he already has. :D :D

Dave

Furby · January 14, 2008, 02:04:34 AM

To figure the 5 to 1 ratio, where do you measure to on the short end on a hinged counter weight model?

shinnlinger · January 14, 2008, 06:28:23 AM

Furby,

We would measure from the pivot to where the hinge for the counter weight hung on the "1"side and to the sling hook on the "5"side.

Dave,

I teach woodshop and building construction among other things now so a call to Ed is probably in order for a variety of reasons. We will see what happens. Maybe I will building a not so mini treb myself.

Furby · January 15, 2008, 12:43:59 AM

On the little ones a straight or uniformed arm is used most times based on what I'm seeing.
When they were actually used and in some movies and such, it appears an entire tree with the taper left on is used for an arm such as Dave was talking about.
What I'm wondering is if the mass/wind resistance of the butt is equally off set by the extra weight in the butt?
Has anyone done any scale models that are actually capable of measuring the small differences?

dail_h · January 17, 2008, 09:12:59 PM

www.trebuchet.com

Dave Shepard · March 30, 2008, 01:00:48 AM

I'm still thinking about this project, but a lack of good trees for the project and not making any headway on the plans is putting a big damper on things. If anyone comes across any full scale information about Warwolf, that would be great. Material costs will go up if I have to buy in the logs for the project, I was going to buy them on the stump, which would have been veeeery cheap. ;)

Dave

plbnyn · March 30, 2008, 09:44:11 PM

saw an article in Smithsoniam mag couple of years back.

zopi · March 30, 2008, 10:54:39 PM

http://members.iinet.net.au/~rmine/gctrebs.html

didn't read the whole thread, but you might think about building a small one..say just big enough to chuck the neighbors yappy little ankle biter back home...i built one about three feet high a few years back...had lots of fun with it despite it's size...

I want to chuck toilets...

Stumpkin · May 11, 2012, 09:36:21 AM

Hi Dave,
I found these free books from Google about the Trebuchet.

http://books.google.com/books?id=vqpDAAAAYAAJ&dq=Trebuchet&pg=PA8#v=onepage&q=Trebuchet&f=false

http://books.google.com/books?id=wXVPAAAAYAAJ&dq=Trebuchet&pg=PA308#v=onepage&q=Trebuchet&f=false

http://books.google.com/books?id=S-1BAAAAYAAJ&dq=Trebuchet&pg=PR13#v=onepage&q=Trebuchet&f=false

Let me know when you build one, I want to chunk a flaming Stumpkin.

shinnlinger · June 12, 2012, 08:44:50 PM

My wood shop class just built a decent sized one with a 55 gallon drum full of water for the counterweight but I can't upload from my iPhone for some reason.

pineywoods · June 12, 2012, 09:11:20 PM

Quote from: shinnlinger on June 12, 2012, 08:44:50 PM
My wood shop class just built a decent sized one with a 55 gallon drum full of water for the counterweight but I can't upload from my iPhone for some reason.

Now that sounds like what I'd be interested in building. Dump the pics off on to your computer...

shinnlinger · June 16, 2012, 11:33:45 PM

shinnlinger · June 16, 2012, 11:52:43 PM

shinnlinger · June 17, 2012, 12:02:55 AM

shinnlinger · June 17, 2012, 12:18:39 AM

We were rushed for time so not all the details got done in the most ideal way (see duct tape instead of muffler clamps) but the machine performed well. If I can figure how to add videos I will show you all a few shots, but we were hucking milk jugs full of water into the woods 60 + yards. The kid who supplied the lumber (dad has a woodmizer) has plans to add a second 55 gallon drum in a welded cage this summer, but I suggested cutting a 275 gallon oil tank in half instead. A random guy swung buy and donated a ruger gun barrel for the pin between the throwing arm and counterweight.

A fun project for sure.