Focus on Competition - 2011/04
Technically Speaking ...
Greg Hahn Technical Director [email protected]
TECH STUFF, Part Two: To reiterate what I ended with last month, the importance of the care and size of wire for servo leads cannot be overemphasized. I don’t know how many times I’ve had to explain to modelers that their servos either didn’t work correctly or at all because of the wire they used for the lead.
I get these looks of disbelief, but you can’t feed a 4.8-volt servo 3.0 volts and expect it to operate properly. And unless you do things right, that could be all the volts reaching that servo out on the aileron 3 or 4 feet from the receiver.
Servos can do some funny things when they are starving for power, including giving up the ghost. Some servos can actually be destroyed by lack of proper voltage, so pay close attention to the lead wire you’re using; it can save your model.
Another issue with wire, especially now since most of the wire we use is imported, is that the metallurgy can often be questionable. Instead of solid copper wire, it is often copper coated and no one knows what the base metal is—so there can easily be problems with compatibility with itself and with other metals it comes in contact with.
Soldering the wires together with either a silver-based or lead-based solder can have a big impact on the compatibility issues, so I recommend the use of a silver-based solder with a light acid flux. Often the use of paste fluxes such as ruby fluid and others will leave too much of the paste behind, and the flux will creep up the wire and cause what I call the dreaded black wire syndrome.
I know you all have seen it, so now you have a name for it. When you cut a wire and you see black instead of copper, you have a problem and the conductivity of that wire is greatly compromised. Replace it immediately!
A BEC, otherwise known as a battery eliminator circuit, is a neat little thing that is built into most electronic speed controllers. The BEC allows the radio system to parasitically operate off the battery used for propulsion, eliminating the need for a separate battery to operate the receiver and servos.
For many of the smaller foamies and stick-and-tissue electrics, the weight savings can be the difference between a flying model and a static model. The problems arise as the size and weight of the model go up. The use of a BEC on a larger, more complex, and heavier model can become a safety issue in a hurry.
One characteristic of a BEC is that when the propulsion battery loses power, so does your radio system since it’s using the same battery. Obviously when that battery will no longer power your propeller, it also won’t power your servos, so your ability to control direction and glide path goes out with it. On a 6-ounce foamie that’s usually not a big deal, but on a 10-pound sport airplane at 60 mph, that is a completely different animal.
I always recommend that any model weighing more than 1 or 2 pounds should have the control system on a separate battery. The weight savings isn’t worth compromising safety and control to the extent that it becomes dangerous to others.
Spring is on the way! Be safe. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
