I’ve been researching the sling/pouch and subsequent tuning. I’ll describe what I found, and if the team is already past this point, then I apologize in advance. Not trying to second guess here …
POUCH DESIGN:
It seems that @Brandon_Green open webbing pouch is a good idea. According to Urban Siege, and their world championship quest, “big solid pouches tend to act as pretty good sails, slowing down the launch speed, and thus killing range. Therefore, solid pouches usually are not used for launching anything rather large, such as a pumpkin (like the 8-10 pounders used in competition).” It clearly needs to cradle the pumpkin, so again … good design on the webbing prototype.
TWO-PART SLING/POUCH:
The few pictures I could find suggest that the pouch and the sling “rope” (sorry - don’t know what else to call it) are frequently two separate pieces. This one from [Yankee Siege] (https://www.pinterest.com/pin/79587118385357648/) shows something very similar to our webbing prototype, using tubular webbing as the “rope”.
I may have misunderstood, but I think we had considered having our pouch webbing extend out and be the “rope” that connects it to the arm, but that would make it difficult to adjust length. We would need a discrete pouch/sling for each projectile size/trajectory combination.
I recommend we find a way to have a separate pouch to attach to our sling “rope”, if we haven’t already done this. This also makes installation easier if we have a field failure of the pouch.
ADJUSTABLE LENGTH:
The larger/more elaborate trebs have a way to adjust the length of the sling to “tune” for different sizes of projectiles/trajectories. This is compatible with the separate sling/rope design concept.
I found this interesting photo. It shows a pouch that has a movable position along a rope. They pass the rope through the fabric sling, which IMO doesn’t seem to be a good idea because of both the fragility and the aerodynamics of a fabric sling. I like the idea, but I’m not sure how we would implement that with a pouch on D-rings.
SLING LENGTH:
Opinions differ on the optimal length of the sling, but these should provide us a starting point:
• The length of the sling is equal to the length of the long arm of the beam (on the payload side) (attributed to Donald B. Siano, in his analysis of trebuchet physics (Trebuchet Mechanics, March 28, 2001).
- The general ratio to start at is a sling length (arm connection to tip of pouch) 80% the length of the throwing arm. Longer length slings have a lower angle of release, good for line drives … Shorter lengths will result in a higher angle of release, best for lobbing projectiles over tall objects.
There is some opinion that higher trajectories (i.e., shorter sling) give more precise shots, in which case an adjustable sling might be useful for the accuracy category. This conceptually makes sense - in the case of a vertical shot the variation in the flight path would be mostly in the Z-dimension so the X,Y variation would be less.
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I volunteered to sew up the pouches, and as you can probably tell, I’m chomping at the bit to get started on this. But I don’t want to do this until we have a little better idea exactly what we’d like to make. I’d love to find a way to test the webbing prototype to see if it’s suitable as a pouch. I’m optimistic that if we make the pouch separate from the sling “rope” then I could be working on the pouches, which I suspect will take longer to make than the “rope”.