cool river --
Yes, I thought about internal weight, but like you said -- with the arm cuff design, it's next to impossible; because the cuff bolt inserts through the shaft, the shaft has to remain hollow -- and as such, there is no room to add counterweighting in the butt-end of the shaft itself. As far the amount of weight needs to be added, there's no "increase" in weight required, that results from the length of the counterweight tube. In fact, the longer the counterweight tube, the LESS weight you need, overall. The science behind it all is explained by "lever/fulcrum" concepts from physics; I'll elaborate, for anyone interested, later in this post.
I totally agree with you that small coils RARELY introduce any substantial balance problems, and yes -- shortening your lower rod DOES help reduce nose-heaviness/improve balance. Totally agreed.
However, I differ with you on the idea that there is "something wrong with the picture" with respect to considering counterweighting of the Equinox. In fact, I'll go so far as to will make the argument that focusing SOLELY on "making a machine as light as possible" is in fact a mistake -- if you wish to make an ergonomically comfortable, well-balanced unit. I know that's not necessarily a popular statement to make, but it's a factual one. The whole "my machine is two ounces lighter than the competitor's machine" may be good for advertisements, and that argument may "sway" a good number of folks, due to its simplicity. But, it does NOT present the entire picture, nor an accurate one, in terms of ergonomic comfort.
I think we can all agree that "light" is "good," and I fully agree that detector manufacturers should seek to make a machine as light as possible. BUT -- while designing a machine to be "as light as possible," BALANCE needs to be considered, as well (again, assuming ergonomic comfort is to be achieved). Here's why...
If you take a look at the Equinox (or any detector, for that matter), and think about it from a science/physics perspective, what you essentially have is long, lightweight shaft (lever), with a relatively substantial amount of weight/mass (the coil) attached way out at the end of that lever. In the case of the Equinox and 12" x 15" coil, we are talking about a pound and a half of weight, out on the end of a lever that measures roughly 40" long (as measured from the handle, out to the coil). And so -- while you may say the coil is "only" a pound and a half in weight, the actual weight you are experiencing when holding the handle of the machine is MUCH greater -- because the force acting on that coil is MULTIPLIED by the leverage effect! In other words, the coil is "using leverage to its advantage." This is where the nose-heavy feeling comes from, and this is ALSO why many folks are experiencing fatigue -- or even pain -- in their wrist/arm/shoulder...because in order to keep that coil hovering above the ground, an upward force -- equal to and opposite the downward force of exerted on the coil by gravity and multiplied by leverage -- must be applied. And guess what has to apply that force? YOU do -- with your hand/wrist/arm/shoulder muscles!
So, if you are experiencing pain or fatigue, while swinging the Equinox, THIS is the reason! YOU have to exert rather substantial effort to keep the coil "levitating" above the ground, and you have LEVERAGE WORKING AGAINST YOU. At this point, there are only a couple of choices, in terms of reducing the amount of effort you have to generate -- use a LIGHTER COIL, or else, APPLY COUNTERWEIGHTING.
To understand counterweighting, it's helpful picture your grade-school playground's see-saw/teeter-totter, or even just an old-fashioned balance scale. Obviously, to balance the force exerted by a given amount of weight on ONE side of the fulcrum, an equal downward force must be applied on the OTHER side of the fulcrum -- and that downward, balancing force is achieved by ADDING WEIGHT, of course. In the case of a metal detector, the handle of the machine is essentially the "fulcrum." And so, adding weight toward the butt-end of the shaft, helps to offset the weight residing on the coil end of the shaft. And thus -- with counterweighting added, you begin to reduce the amount of effort/force that YOU have to apply, to keep the coil floating above the ground. And, again, using concepts of leverage, the farther toward -- or even beyond -- the butt-end of the shaft you apply the weight, the more you are using leverage to YOUR advantage, and thus lesser overall amount of counterweighting will be required.
The problem with the Equinox, is that there is essentially ZERO weight on the "butt-end" side of the fulcrum (handle). Some machines, such as the CTX 3030 for example, have batteries, etc. near the butt-end of the shaft, which -- based on the arguments I'm presenting here -- results in a much better-balanced (though heavier) machine. With the Equinox, however, having essentially zero weight out beyond the handle, you have the perfect recipe for a nose-heavy (non-ergonomically comfortable) machine.
The bottom line is that what I have written here, is the logic/scientific reasoning behind why I designed the counterweights. While I understand -- as you stated, Chuck -- that it seems a bit counter-intuitive at first to ADD WEIGHT to a machine, after begging Minelab to make as light as possible, the fact is that ABSOLUTE weight is NOT the entire picture; the DISTRIBUTION of the weight is also important, if you wish to achieve a comfortable machine.
The last thing I'll say is -- this is why my counterweight is an OPTION, and not "standard equipment." There are indeed those who do not want to add ANY weight to the machine; in fact, many folks hope to REDUCE overall weight, by switching to a carbon-fiber shaft. And of course, my shaft does reduce the overall weight of the machine, and so these customers are the ones who choose not to purchase the counterweights. BUT -- I also know that the machine becomes more comfortable to swing, for those who struggle with the nose-heaviness, whenever counterweighting is applied. Every ounce of counterweighting that is added, absolutely, unequivocally REDUCES the amount of effort that must be exerted by user's hand/wrist/arm/shoulder. When a "proper" amount of weight is added, the machine simply becomes more pleasant to swing -- and there are a bunch of people who have added counterweighting to the EQX, who can attest to this. It's simply science...