For the obvious reasons, I invariably get too busy to blog exactly when things get interesting...
Wagner Smith T1DPT
If this isn’t the world’s most forced pun, I don’t know what is.
A central part of setting up the games is to get the 1 km vertical cable raceway in place. The idea is to keep most of the cable on a spool, and have the helicopter pull it out, with the spool offering controlled resistance. The process will be stopped by either increasing the resistance of the spool to above the helicopter’s pull force, or reducing the helicopter’s pull force to below the resistance of the winch.
The requirements on the winch are simple: It has to work with at least 3000 feet of 3/16″ steel cable, it has to pull at anywhere between zero and several hundred pounds, and at speeds of zero to several meters per second (we want to cover 1000 m in about 5 minutes, so 3 m/s would be grand), and it has to work in both active (reel-in) and passive (pay-out) modes.
Turns out this is a pretty tall order. Most winches do not go this fast, and if they do, they are weaklings.
Tow winches are too slow, and can’t take that amount of cable. Overhead lift winches – just the same. There are the winches used to launch gliders, but they are too fast and uncontrolled. Elevator motors are probably interesting, but I can just imagine the cost of building a portable elevator winch.
Luckily, we found an application with similar requirements – stringing power lines. These are km-long operations, in which cable is pulled and tensioned as it is being fed into pulley on the power lines. Perfect. And the bonus is that often these operations are done with helicopters, so there’s precedent to using them in a fashion similar to what we’re doing.
The winch motor is hydraulic, which means there’s somewhat of a “soft touch” to it, and the breaking mechanism uses the engine as a hydraulic brake. Perfect.
The problem right now seems to be locating one. The king-of-the-hill is Wagner-Smith equipment, but these units are in strong demand and the nearest one I can find is located in Texas. $2000 just to get it here, and probably another $4000 to rent. Ouchie again. (and another reference to the “Help Us” box on the right!)
But the upside – we have the right winch. As a bonus, it a load cell measuring cable tension – very useful. It also has a ground lug, which allows us to electrically ground the cable (more on that later)