The ‘power drum’ concept is a go! But first, a little background on the counter-weighted arbor systems that are used in fly systems of this sort.
The basic idea is to lessen the forces involved in lifting objects using a counterweight design. This counterweight should ideally be 50% of the weight being lifted by the elevator, and because that weight can change drastically it makes sense to design a process that will allow the easy addition/subtraction of counterweight from the arbor. The arbor houses the counterweights and acts as the object the lifting and lowering cables physically attach to. Here’s a sketch of the proposed arbor – click on it to magnify…
The weights (which are steel slabs with u-shaped grooves cut into them) pile ontop of one another and are held in place by weight locks. These locks could be anything from pipe clamps to rings with set screws and holding plates. The lifting and lowering wires, as well as the wire control to the power drum, will be physically connected to the upper and lower arbor plates. These plates will also be guided vertically to impede any rocking or swinging of the counterweight.
The power drum is what physically transmits power from the hand crank or electric winch to the arbor system. It is the power drum wires labeled ‘PD’ in the drawing above that connect the weights to the power drum, and they are skewed to either side to allow the wire to wrap around the drum in the center, as the 2 wires spiral in toward eachother.
This is more easily seen than described…so heres a sketch of the power drum wire setup…The manufacturing constraints on fabricating the drum limit the diameter to 10 inches, so that’s the size of the drum I’ll design to. The outer surface will also have grooves cut into it to allow for 1/4″ steel cable to lay securely around the drum face.