Floating Arm Trebuchet ™
- Competition Version
The new, stronger F.A.T. Guillotine-Style Catapult
Designed and made in the USA for
better quality, better performance!
This version of our 21st century trebuchet is manufactured from top-quality solid oak non-
toxic formaldehyde-free domestic plywood. Plywood is more dimensionally stable, a lot stronger, and a
lot less expensive than natural hardwood.
The F.A.T. is an updated version of the ancient trebuchet, designed from a modern understanding of
physics and engineering principles for incredible power and range!
This version of our most popular kit incorporates several improvements over the old model, including our
new "gap-hop" architecture - now the wheels gently hop over the gap in the tracks instead of pounding
over them, eliminating the destructive "thump-bump" of the old model. This enables us to use positive
tracking wheels - no more frame-strikes! The wheels are locked-in to a track system that prevents them
from drifting off-course during firing. We've also added a turnbuckle based pin angle tuning mechanism,
for non-slip ultra-fine tuning of the pin angle. All major improvements for accuracy and repeatability in
this one-of-a-kind machine! Just fill the counterweight boxes with anything from coins, nuts and bolts,
BBs or anything heavy enough to give you five to seven pounds per box. The box dimensions are 2" wide,
5.75" long and 4.25" deep, for a whopping 48.8 cubic inches of volume.
Engineered using modern mechanical principles and computer aided design, this mini-powerhouse
can hurl a golf ball over 250 feet. It uses guillotine action and a plunging beam to maximize
potential energy and a floating arm to convert that energy into projectile motion. Precision crafted of top-
quality engineered plywood, the kit contains everything you need to build a working model.*
The trebuchet is essentially a gravity powered energy conversion machine, turning potential energy into
kinetic energy and using it to throw a ball. It's a great way to see classical mechanics in action! Similar to
the forty-foot tall, 25 ton behemoth " target=itnos>T-Wrecks" we built on the TV show "In The Name Of Science" (2004, The Discovery
Channel), except this model is only 34 inches tall, 18 inches long and 7 inches wide, but it
hurls more than five times as far as T-Wrecks in scaled distance.
A common complaint from engineering professors is that "Students today have a great understanding of
computers, but fewer and fewer of them have any real hands-on, real-world understanding of physics and
mechanics." Our kits are designed and intended to spark an interest in real-world science and
engineering, and maybe even a bit of history too!
The detailed instructions (14 pages!) are complete with diagrams, photos, tuning tips, equations for
calculating the machine's efficiency and more! All parts are pre-cut, pre-drilled and can be assembled to a
finished model in one evening (plus glue drying time).
We've put a lot of time and effort into making this kit as easy and complete as possible. It's a fun way to
learn about physics and engineering!
Tools required:
Scissors, Glue, Ruler, a utility knife, small wrenches (for one 1/4" bolt and one 3/8" bolt). Sandpaper is
optional.
Assembly time:
For a Master carpenter doing a sloppy job: about 2 hours.
A person with no kit building experience being extremely meticulous: two or three days.
The model in these photos was built by Ron Toms in about four hours.
Assembled Size:
- Height: 34"
- Length: 18"
- Width: 7" (frame) 12" (with counterweights attached)
Additional Counterweight Required:
- 10 to 18 lbs.
(Loose nuts and bolts, coins, rocks, anything that
can fit into the included plywood boxes.)
Range:
- Golf balls, up to 250 feet
- Tennis balls, up to about 120 feet.
(Optimal range assumes a well tuned machine)
Shipping weight: 12 lbs.
Box dimensions: 36" x 12" x 4"
Quantity pricing info:
0 to 4 kits, standard price.
5 to 9 kits, 10% off
10 or more kits, 15% off
Orders of $200 or more qualify for FREE ground shipping!
WARNING! This is a functional model intended for educational demonstrations of physics. It contains a
fast moving arm and projectile that can cause injury if you make contact when firing. Use only under
strict, competent adult supervision.
* You'll need to supply the counterweight material. Anything from nuts and bolts, BBs, coins, sand or a
good fist full of pebbles will do!
* Can throw 250 feet when properly constructed and tuned with sufficient counterweights. Your
performance may vary.
* FAT, F.A.T. and Floating Arm Trebuchet are trademarks of RLT Industries.
If you are buying this model for the Science Olympiad:
There is a rule which requires the trebuchet arm to remain stationary when the counterweights are
removed and the trigger is pulled. The original intent of this rule was to disqualify springs and bungee
cords from the trebuchet competition.
Since the FAT does not contain any springs or bungee cords, it does not violate the intent of the
rule, even though it does violate the letter of the rule. Keep this in mind if you ever become a lawmaker -
good wording is difficult and extremely important in order to keep the intent, without doing harm or
injustice to innocence.
If you want to use the FAT for your competition, there are options. First, I'd recommend negotiating with
your instructor or judges, let them know about the problem and the intent of the rule, and see if you can
get an exemption from it. This has worked for other folks in the past, but not always. It depends on how
reasonable your judges are.
If that fails, here's another strategy that has worked. The rule states that the arm cannot move when the
counterweights are removed and the trigger is open (unset). In this model, the arm is part of the
counterweight system. Its center of gravity falls as part of the launch sequence and the arm's weight
(including the wheels and wheel carriage) contributes to the total energy transferred to the projectile. You
should be allowed to remove the whole arm assembly to satisfy the "no motion" rule. In fact, since the arm
is part of the counterweight, if you are not allowed to remove the arm during this test, then your judges
ARE violating the letter of the rule in regards to this test!
Once the arm is removed and set aside, it will not move when the trigger is pulled, and the test is passed.
Of course, the decision whether to accept these lines of reasoning are entirely up to the judges of your
competition. It would be wise to check with them first before purchasing this kit. If they will not allow it,
then the SPECK or the TK3 are your next best options, although
nothing performs better than our FAT!
More info about SciOly and the FAT can be found here
Good luck with the competition!
