Other RC Parts & Components December 14, 2006
You want to measure the power system of your electric rc helicopter or remote control airplane. This article discusses why, what you can measure, and how you can measure it.
Or maybe you don’t particularly want to measure your aircraft’s power system. But you should. Why? Because you spent money on your power system, and you might not be getting everything out of it.
What Is An Electronic Power System
Your power system is a combination of propeller, motor, speed controller, and battery. Each of those is good at something. Are you taking advantage of that? A 25A speed controller (for example, the Castle Creations Phoenix 25) in a 7oz foamie drawing 5A is not being used properly. By measuring your electric power system you can discover mismatched equipment and correct it. In this example, a Phoenix 10 ESC would save weight.
It’s a complex universe; you’ll never understand it all, but you don’t need to. Humans have figured out that numerically describing a few things is good enough. For us electric modelers, the numbers we use describe electric current flow (unit of Amps, A), electric potential (unit of Volts, V), and temperature. We’ve found it best to measure current and voltage with a wattmeter, and temperature with an infrared temperature gauge.
A wattmeter is connected between the battery and the speed controller. Among other things, it displays the voltage and current. You should mentally note the voltage and current readings while the aircraft is at full throttle, and write them down after you’ve disconnected the battery.
Current And Voltage
The current reading should be within the limits of the speed controller, battery, and motor. The voltage indicates how your batteries are performing. Usually you can confirm your battery is adequate by noting that current is below the battery’s rated max current (For Thunder Power batteries, this would be the continuous rating, not the burst rating). This rating generally says ‘this battery model is approved for this use,’ whereas voltage says ‘this battery is performing as expected’ or ‘this battery can’t handle this.’ As a rough guide, your lithium polymer battery voltage at full throttle should be above 3.3V per cell (i.e. a 3s lipo should be above 9.9V).
The temperature gauge is used to tell you the temperature of your motor and batteries immediately after a flight. For both, the key temperature is 60°C (140°F). Both should be under that temperature. Above this temperature, lithium polymer batteries are permanently damaged, while motors lose efficiency and become dangerously close to demagnetizing and burning the windings. However, being too cold isn’t ideal, either. Cold is a sign that the motor isn’t being properly used (i.e. it’s too big), and cold batteries don’t put out as much power as 50-60°C batteries.
An electric expert is someone who puts together a power system that is slightly conservative. He’ll test and measure that system, and then prop up based on those measurements. The second prop will perfect the power system: currents will be near every component’s limit, and temperatures after a flight will be ideal. At that point, every component will be played to its strength. Thereafter is the fun part that we call flying.
|» Next||Thunder Power 1010C Li Po Charger – Tips & Tricks|
|« Previous||Thunder Power RC 205v & 210v LiPoly Balancer Tips & Tricks|