Pouch Design
In the picture on the right, at position 1, the opening to the pouch is
facing up.  The back of the pouch is starting to be pulled.  In the next
position the back of the pouch is pulling more and in the third
position both the opening and the back are almost parallel.  

This is a key feature, because I've seen many designs that also give
the backspin, but they do it at release (not during the throw) which is
very hard on a pumpkin.  This can cause the pumpkin to break apart.  
And, this type of release is a big energy drain - it's pulling on the

The release pin on the sling is tied off on the TA with a few feet of
slack, so that when the release occurs, the ring on the release side
doesn't flail around after the pumpkin is long gone.  

In addition, I didn't want anything in front of the pumpkin at release.  
And I wanted the release to be gentle.  Remember, that 10 lb
pumpkin is generating 1,200 lbs of pressure on the sling - this is
running at 200+ mph.  So, the pumpkin is rolling down the side of the
pouch, and at release, it's already at the opening.  

The basketball net opening is released when the release ring falls
off the TA pin.  To emphasize the smooth release, the picture to the
right shows the pin release, how the wind blows the pouch open,
and then blows the pouch gently off the pumpkin.
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Pouch Design
I have experimented with many pouch designs.  I bought a walking
foot sewing machine so I could stitch heavy strapping material
together (cost me a small fortune).  The best pouch design for King
Arthur and Merlin is using a basketball net.  I've improved it by using 2
nets, one inside the other, but the design is the same.  

Objectives of the design:
•        Create a back spin on the pumpkin without using any energy
•        Have a clean release - nothing in front of the pumpkin at release
•        Have a smooth release to prevent breaking the pumpkin.  Need
to be as gentle as possible
•        Hold the pumpkin without danger of falling out prematurely  

I take the 2 nets, and tie the long pieces together (the ones on the top
of the net if it was mounted on a hoop).  This will become the base of
the pouch and will attach to the anchor side of the sling on the
throwing arm (TA).  The release side of the sling is tied to a number of
loops on the other side of the pouch.  This number changes over time
because the net is made out of nylon and it stretches.  

Throw dynamics:
Looking at it from the point of view of the pouch, the sling on the
release side is shorter than the anchor side and their attachments are
separated on the TA.  In the case of King Arthur the separation is 14
inches.  As a point of reference my sling length is 14.5 feet.  

The reason for this separation is so the pumpkin will roll down the
side of the basketball net going toward the opening during the throw.  
The objective is to get the pumpkin spinning backward so I can take
advantage of the Magnus Effect.  
I adjust the release side of the sling to the desired length.  This
length is obtained from simulations using Working Model 2D and
analysis of past throws caught on video.  

With the throwing arm semi-cocked so I can work on the release pin,
I attach the release ring and move the pouch/sling to 90 degrees
from the TA.  

With the ring secured on the release pin, I walk the pouch forward
until the sling gets to 130 degrees off the TA.  This will give me a
rough idea where the pumpkin will be in the pouch at release.  I
adjust the anchor side of the sling so the pumpkin is at the mouth of
the pouch.  

Now I'm ready to go and I can finish cocking the machine.    

One last point, I usually don't change the Pin angle - it stays at 130
degrees.  I adjust the throw height by changing the length of the
sling.  My  objective is to have the longest sling length King Arthur
can swallow.  This translated to a pin angle of 130 degrees.  

Shorter sling - higher throw............  

Enjoy your engineering experience.