Everyone --
After a couple of days of thinking, partially shaped by feedback from many folks (thanks to all) -- I believe I am very close to finalizing the design for the counterweigh system, enough to order parts for prototype testing. My plan is to produce the counterweights from 35mm O.D. x 33mm I.D. carbon-fiber tubes. They will screw into the butt-end of the shaft via threaded connectors, and will be capped by a threaded end cap. The threaded end cap will allow for easy addition/removal of weight, as the customer desires. I will also be purchasing a supply of heavy-duty ziplock bags, which will be of roughly the same diameter as the inside of the carbon-fiber tube. The bags will be of various heights -- to accommodate several different amounts of weight (lead pellets). I will ship either WITH lead included, or without, depending upon customer desire. I plan to supply 2" tall bags (to accommodate roughly 8 - 10 oz. of weight), 3" tall bags (to accommodate roughly 12 to 15 oz. of weight), and 6" tall bags (to accommodate roughly 24-30 oz. weight).
Using 35mm O.D. tubes, the top of the counterweight tube will be on the same plane as/flush with the bottom of the arm cuff. I expect to be able to keep the weights to a maximum of 6" length or less, per customer specification (6" being long enough to accommodate the weight needed to fully balance the 15" coil). Purchase of a roughly 6" counterweight would therefore allow any combination of weight (via pellets in the plastic bags) to be added or removed, simply by removing the end cap. Shorter counterweights will be constructed in the same way (likely in roughly 2" and 4" lengths), and -- while still including the threaded end cap and plastic bags, so as to be "customizable" in terms of the amount of weight, the shorter-length tubes would of course not accommodate quite as much weight.
At this point, calculations show that 2 1/2" or so of tube length will hold roughly 12 oz. weight, 4.75" or so will hold roughly 25 oz. of weight, and 5 1/2" or so will hold 28 oz. weight.
I chose to specifically mention 12 oz., 25 oz., and 28 oz. as the weights to use as example tube lengths, for this reason:
Assuming "average" lower shaft adjustment length, and a "reasonable" shaft angle, relative to the ground (i.e. swinging the coil a moderate/reasonable distance out from your feet)…
12 oz. is roughly the amount of weight needed to COMPLETELY BALANCE the machine with 6" coil.
12 oz. is ALSO roughly the amount of weight needed to offset the weight difference between the 6" coil and the 12" x 15" coil; said another way, 12 oz. counterweight will make the machine feel the same when swinging the 12" x 15" coil, as it would when swinging the 6" coil with NO counterweight.
25 oz. is roughly the amount of weight needed to COMPLETELY BALANCE the machine for the 11" coil.
28 oz. is roughly the amount of weight needed to COMPLETELY BALANCE the machine for the 12" x 15" coil.
I would like to stress again, that it's completely up to the user as to the amount of counterweight which is "right" for their needs/desires/preferences. Some may wish for COMPLETE balance, for the larger coils; others may wish to only offset the additional weight added when using one of the larger coils. Still others may wish only for a few ounces of counterweight, just to "help a little." And of course, MANY folks will prefer no counterweights at all -- preferring instead the benefits of a lighter machine, as afforded by the carbon-fiber shaft without counterweights.
The bottom line is this -- this design of the counterweight system will allow complete customer flexibility in terms of exactly what length of counterweight they wish for me to produce for them, and exactly what amount of weight they wish to include in that tube.
Thanks all, for all your input. These interactions have been quite helpful toward finalizing the design. I think that at this point, with the weights as an optional accessory, this design will allow the most flexibility possible in terms of individual customer wishes -- ranging anywhere from NO COUNTERWEIGHT AT ALL (and thus a lighter machine than when using the stock shaft system), all the way up through fully balancing the 12" x 15" coil via roughly 28oz. counterweight -- plus any other combination of desired counterweight/balance in between.
Thanks!
Steve