Maintain flexible drive cables

Radio Control Boat Modeler, Dec 2001 by Eyrich, Rick

Easy tips for reliability and performance

Whenever a flexible drive cable is used on an RC boat, the possibility always exists that the spun-wire cable might break inside the cable liner or even separate from the boat altogether. These cables have to endure incredible stress from prop impacts, poor water quality and improper maintenance. It benefits the average boater to know as much about these flexible drivelines as possible. The following tips and techniques will enable you to extend the average cable's lifespan and reduce its chances of prematurely exiting the boat-usually with your best prop attached.

1

With most RC boats, maintaining the flexible drive cable requires only a few basic tools and materials, most of which are found in a modelers toolbox Besides just servicing these cables, you can also apply a few simple techniques to increase their reliability, cut down on the amount of drag they produce and eliminate any moisture that might creep up their length and into your hull. These improvements won't empty your wallet, and they should improve your boat's performance out on the lake.

2

Soldering a mufti-strand metal drive flex cable to a stub shaft requires either a high-watt soldering iron or a light-duty torch to properly "sweat" the solder between the cable and the shaft. As for the solder itself, some boaters use silver solder; others rely on regular rosin-core 60/40 solder. Alternatives include lowtemperature silver solder and some brands of gunsmithing solder, but with any of these, you should use a good soldering flux compound to help the solder adhere.

3

One way to reduce the friction between the flex cable and its stuffing box involves giving the cable a good burnishing with WD-40 lubricant and 400-grit wet/dry sandpaper. This process will remove any minor burrs and rough edges from the cable's outer surface. Plus, if there are any tiny flaws in the cable itself, this technique will likely bring them out. Once the cable has been thoroughly sanded, it should be given a serious cleaning to remove any leftover sandpaper grit that might have worked its way between the cable strands.

4

For those RC boats that use a drive cable with an unlined stuffing box, a further polishing beyond the WD-40/sandpaper technique is useful. Before you fit the brass stuffing tube to the hull, apply some automotive polishing compound to the flex cable and then chuck the cable into a variable- speed drill. Then, while holding the tube, slowly spin the cable and move it back and forth inside the tube. You'll want to spin the flex cable in the same direction, as it will be turning the propeller, cranking it the other way could "loosen" the cable's metal strands. After you've given the stuffing-box tube and cable a good compounding, they must both be thoroughly cleaned. When the cleaning is finished, you can install the stuffing box in the hull and know its interior is ultra-smooth.

5

For fast electric boats, there is an alternative to the regular steel flex cable driveline setup. Commonly called a "piano wire" drive, this arrangement uses a metal-, plastic-, or fiberglass-tube stuffing box, but instead of the flex cable, a 16-inch-diameter piano wire is used to transfer power from the motor to the propeller. Other suitable small-diameter-wire drives can be built around dental-brace wire, stainless steel heli-arc rod and Teflon-coated mountain-bike control cable. The idea of using alternative materials in place of traditional cable is becoming popular in fast-electric boat racing.

6

If your boat's flex drive allows moisture into the inner hull through the stuffing box/cable, try this quick and easy way to seal the junction point using regular silicone tubing. Fit one end of a short piece of flexible silicone fuel tubing over the tip of the stuffing-box tube, and slide the other end of the fuel tubing onto the flex cable itself. You may have to try various sizes and brands of silicone hose to get the right fit (i.e., not too tight on the drive cable); but once the tubing is in place, there will be little chance of any water coming up through the stuffing-box tube. Some boaters will even back up the inner tubing seal with a secondary silicone hose attached at the point where the tube exits the hull, thus doubling the seal on the boat's driveline assembly.

7

To prevent the loss of the flex cable and/or the propeller, some boaters position a standard RC aircraft locking wheel collar between the motor or engine cable clamp or collet and the stuffing-box end. Up to a 4inch-diameter flex cable can be fitted with these wheel collars, and in the event that an engine/motor collet comes loose, the cable and prop won't end up on the bottom of your local pond. On smaller flex cables ,a stiff. rubber Ol-ring works almost as well as the wheel collar; plus, it adds less weight to the driveline. One concern is that the collar could cause a driveline imbalance, but so far, this hasn't proved to be a problem. Using these metal locking wheel collars will keep your replacement shaft/propeller costs down to a minimum.