What Are Electronic Speed Controls (ESC’s)
There are two main types of ESC, for brushed or brushless motors. You cannot use a brushed ESC with a brushless motor or vice versa. Think of the features you will need like a brake and soft start. You will need a brake if you are using a folding prop and a soft start if you are using a gearbox and an on/off switch for a throttle. These features can often be found on Radio Controlled Sailplanes. The most important thing to consider when choosing an ESC is matching the ESC to your motor. It is good to use an ESC rated at a higher amperage than you intend running your motor at as an insurance against over stressing your ESC causing failure and potential damage to your model. Often you will see a burst rating for an ESC, meaning you can run the ESC at a maximum Amperage for a limited time, and exceeding this limit is asking for trouble. Most sensible aeromodelers like to have an esc capable of 10 to 20% more Amps than they plan to use depending on its quality. You will need a meter to measure the Amps and Volts being generated by your power system to ensure you are not stressing the battery, ESC or motor.
What is a bec? Bec is an acronym for battery eliminating circuit. This device provides power for the servos in your model. Many ESC’s have a bec that can only handle a certain number of servos at a given voltage. The higher the voltage you use the less servos you can use. Using too many servos from the bec in your ESC will cause overheating and failure of the bec. This will be catastrophic if your bec fails in flight so how can you safely run more servos with your ESC? External bec’s, or Ubec’s use power from your flight battery pack and are a cheap way of safely using more servos than the bec in your ESC can handle. A receiver battery pack is another way of supplying reliable power to your servos without using the bec in your esc.
Cut off voltage
Set the cut off voltage on your ESC to 3 volts per cell to ensure you don’t over discharge and damage your lipo pack.
How To Choose the Prop?
The propeller is the component that puts a load on a power system. With the wrong prop you can damage your battery, ESC and motor. Think of the prop like the gears in a car. Some props are like first gear and the motor will have to work at high rpm to go slowly. If you have driven a 4X4 you will know that this gives you power to climb steep hills at low speed without stalling the engine. You could compare this to prop hanging a 3D model where power is more important than speed. On the other hand you might want to go fast. This will require a prop that is more like the top gear in a car. It doesn’t have the power to take off and climb a steep hill at low speed, but once up to speed it can maintain that speed comfortably. The numbers on a prop, say 10X4, give you the diameter and pitch. In this case you would have a prop with a diameter of 10 inches and a pitch of 4. A 10X4 prop will give you more thrust at a lower speed like the 4X4 analogy above. If you swapped it for a 10X7 prop you would have a higher top speed, but your take off run would be longer. The extra load on the motor would also draw a higher Amperage.