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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 newest version of our 21st century trebuchet is manufactured from top-quality engineered hardwood plywood. Plywood is more dimensionally stable, a lot stronger, and a lot less expensive than natural hardwood. NOTE: This version ships without counterweights so you can choose your own. Just about anything heavy will do*

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! (Shown with optional accessories in these photos)

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!

Engineered using modern mechanical principles and computer aided design, this mini-powerhouse can hurl a golf ball over 200 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 "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 15 lbs. of counterweight such as barbel weights (sold at any fitness stores), weight bags (such as a pair of socks filled with metal nuts, bolts, coins, gravel and sand, etc...) or anything that can attach to the 3/8" by 4-inch long mounting bolts.

- Golf balls, up to 200 feet
- Tennis balls, up to about 100 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 200 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!

* This model requires about ten pounds of counterweight, up to fifteen pounds. You can use any kind of counterweight that will attach to the included mounting bolt (it is 3/8" diameter and extends four inches on each side). We've used sandbags made from old socks, filled with rocks and sand or nuts, bolts and coins, etc, standard barbel weights work great, or you can even use the same Steel Boxes as we use in the other version of this kit. (steel boxes sold separately)

Barbel weights are the most common choice, and we include large washers so they won't fall off the bolts. These weights are consistent, easy to manage and won't spill, and are available at most fitness and sporting goods stores for around forty cents per pound (we recommend using four 2.5 lb weights for 10 lbs total).

Sand bags, or nut/bolt/coin bags, are great because you can easily fine-tune the weights for target shooting, and you can prepare multiple bags of different weights to use in the field and for experiments. Bags made from socks can be quickly and easily swapped just by draping them over the 4-inch bolts.

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    Price: $139.00
    Minimum age: 14
    Availability: In stock.

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    Item code: 10102

So, why do my kids
need this stuff?

Seriously, get some toys, go outside and play. It's good for you. Spend some quality time with your kids, your buddies or just get away from the TV and computer long enough for a good dose of sunshine.

Learn a new skill. Get some exercise. Make someone happy. Make yourself happy. Set-up some cans and knock them down, just to see if you can.

Teach your kids something about safety, posture, focus and concentration. It's easy if they have something fun to do while they're learning it.

The science of Physics was founded on the principles of ballistic motion. What better way to develop an interest in physics than to play with ballistic toys? And you know where that leads... First, physics, then math, engineering and economics. Next thing you know, he'll be studying medicine with plans to become a ridiculously high paid sports doctor with a keen knack for investing, all because someone bought him a projectile shooting toy gun as a kid. How's that for a reason?

Here's an even better reason- kids like to play with their parents and they like to compete. Do some target practice with your kids in the backyard. It's far better than watching re-runs of some lame TV show or turning into a video game zombie! Parents and kids need to interact. It's our goal to provide the toys that make it easy. We're doing our part, now you need to do yours.

So, one more time, get some toys and go outside and play!