The initial starting point for Merlin design was a FAT (Floating Arm Trebuchet) type design. I wanted to
keep the key measurements of the design as close to King Arthur as possible in order to provide a
comparison - the CW (counter weight) of 600 lbs and the TA (throwing arm) of 12 feet. But when doing
kinetic modeling, the best throw I could concoct was considerably less than acceptable. In studying the
FAT design I uncovered three major design points that I thought I could improve upon.
1) On a FAT the tip of the throwing arm is moving the fastest when it is going horizontal (a big reason why
large FATs tend to throw flat, distance robbing trajectories). In order to get closer to the desired 40 degree
trajectory I had to release the payload before the fastest tip speed. This produced a lack luster
payload speed of 110 mph.
2005 - Merlin Functional Design
To solve this, I tilted the horizontal track 40 degrees. Now the payload releases when the
arm tip speed reaches its fastest point.
This tilted track design showed a huge improvement in speed – from 110 mph to 177 mph.
So why not start the throw further up the horizontal plane? After all, the tilted track design
allowed me to do exactly that.
Again – another big improvement to 199 mph.
2) There are two tracks that intersect in the FAT/F2K design, the vertical CW track and horizontal roller
track. This means that the rollers have to traverse a gap in the horizontal track. There have been some
ingenious designs to solve this problem including a flap that covers the gap after the CW passes. After
a brainstorm in the middle of the night (I do some of my best thinking then) I moved the vertical track to
the right so the CW runner never crosses the horizontal track. The results are the L shaped pieces that
travel on the tower structure of Merlin.
With all these improvements the results are very similar to King Arthur. However Merlin needed to do
I could make it bigger or I could add weight – but I ran into the law of diminishing returns and I wanted to
improve performance using design, not a larger TA or more CW. So there was one more thing I needed
3) In the FAT or F2K design the height of the CW has a corresponding effect on the distance. However
CW height on a FAT/F2K is limited by the length of the TA. It just can’t go up any higher. So why not
disjoin these classical connections and make the entire throwing mechanism float. This means that I can
hoist the throwing mechanism as high as is practical. The following picture is the original design that
gave birth to Merlin.
The results, a speed of 257 mph. This was very encouraging and spurred on a flurry of activity. In fact I
went on to make some 80 different versions/modifications of this design before I settled on the final
production functional design.
The project is only started. The machine is 50 feet tall – how do I get it to Delaware? Obviously I had to
figure a way to collapse the machine for transport. And how would I support the enormous forces?
The engineering effort needed to address these 2 issues took much longer to finalize than the original
design work. Again, 45 more kinetic versions and compromises to get a 50 foot tall mechanism into a 13.5
foot high folding mass.
This functional spec became input to the final design. I have engineers on our team – and they think in
AutoCAD. So I had to learn how to build 3D AutoCAD drawings and build these incredible works of art.
During this exercise I found multiple issues with my functional spec. For example, I had one of the hydraulic
cylinders going right through the support structure for the J track – so I moved it to the tower. Going back
and forth between the functional spec and the final design became an iterative process. More versions…..
I suppose if this wasn’t my first effort it would have gone much smoother. I was learning about these
extraordinary engineering tools as I was going.
All this effort was to solve a problem that I didn’t have with King Arthur. When building a smaller machine,
you can pick up a piece, hold it in place to measure, mark it, cut it, put it into place. This was not possible
in the case of Merlin – the pieces are too big. It requires a tractor with a loader to move these 600 lbs
parts. So I had to develop a detailed design so I could build all the parts and then put them together and
hope and pray they all fit.
The engineers came down and showed me how to layout the main structure, get it level, and spot weld the
joints in place. This can be a daunting effort considering this is a 1/16 of and inch at the end of a 50 foot
piece. They wouldn’t let it go until it was right on. Then, one hot weld – and the warp will move the end of
the part 2 inches or more. Testy beast…… isn’t it…..
Many of you have seen the results.