What is the FAKA?
The FAKA is a trebuchet design invented in late 2006 by Craig Macomber. It stands for Floating Axle King Arthur. It combines the efficiency of a Floating Arm Trebuchet (FAT) with the increased potential energy of a King Arthur.
Basically, it gets a lot of energy for it's size and weight, and uses it very well, but there are many challenges. A FAKA is a very high end trebuchet form the efficiency perspective. They work great over a huge range of mass ratios. The FAKA is very efficient for its frame height and arm length as well. FAKAs are hard to build, and have have a tendency to go very wrong, and often break things, if the timing is a little off.
Disadvantages of the FAKA
The combination of FAT and KA does have a cost. It's hard to build, and unstable to operate. In the simplest setup, there is nothing designed to absorb energy, and it can not swing back and forth like most trebuchets until it stops. The leftover energy goes into battering the axle trucks into the stops, and the hanger into the upper arm stop. Of course, when properly tuned, there is very little energy left (The FAKA can be tuned for very high efficiency), but before its tuned, or in the event of a misfire things can go quite wrong. Several arm derailments have been caused by this.
My FAKA has misfired once, and it lead to the wheels smashing into the front stop and derailing the arm. This was with 5 pounds of CW. It has derailed several other times, but so far no major damage has occurred.
Also, the Golf Ball Beast lifts the back of the frame just before the arm is released. This is bad because it adds stress to the frame when it re-contacts the ground, and could (And I think it did) derail the axle.1
Design of a FAKA
FAKAs have several parts, most of which are similar to other types of trebuchets.
Below is a picture of the first FAKA ever made with the important parts which are shown labeled.
The upper arm stop is very important. It must hold the boogies or trucks tight against the stop. If it does not, the arm will slam into one then the other before it is released. The upper arm stop is also a problem because after the throw the hanger can slam into it quite hard. On my larger FAKA, Golf Ball Beast, it is hinged so it can get knocked a little bit out of the way.
The boogies, or trucks, which ride the tracks, need to prevent the axle from twisting relative to the frame, If one side gets ahead of the other, it will likely jam, but the counterweight or the arm might also strike the frame. This is why more than one wheel is used. The further between them the better they will reduce this twisting.