Continued… The Control in E-systems:

So, the last part of the “system” of motor-battery-propeller mystery is the ESC, or Electronic Speed Controller. These expensive little toys are simply a means to convert the variable throttle position on the transmitter to an output power to the motor via the receiver in the plane. They do far more than this, and are far more sophisticated than you may think.

There are fundamentally two types, one for brushed motors (straight proportional DC output) and one for brushless motors (3-phase AC output). Other skews in this device are about the BEC, or Battery Eliminator Circuit.

The conventional ESC provides one connection that serves two purposes… one is to supply power to the control system via the receiver connection on the throttle channel (that’s the BEC), and the other is to act as the input for the throttle signal from the receiver. The connection is a typical 3-pole servo-type connector on a lead, again, plugging into the Throttle Channel.

A note here: It is not clearly documented, but you may supply power to the receiver, and hence servos, via any of the “outputs” on the conventional radio receiver. This was confusing to me at first, because we are getting power “from” the ESC and sending proportional throttle position signals “to” the ESC thru a single connection.

As I can tell, the BIG ESC’s generally omit BEC power supply because the practice is to provide a separate power source for driving the servos and receiver. Those platforms rely on separate isolated power systems just like on fuel aircraft for safety and reliability.

ESC’s are rated by their Amperage Capacity. This is the current load that is drawn by the motor from the battery thru the ESC. These devices do not limit the current, but they do generally have overload protection. So, you may pull more current than they are rated for, but when you do this, they will heat up and may trip thermal overload circuit protection. Most ESC’s, when overloaded or overheated, cut power output to the motor, but continue to provide power thru the BEC so the flight control systems are not lost.

Good cooling is necessary for the ESC, particularly if you are pushing its limits. It is recommended that the ESC be located in a space where it is in a free flow of air. Do not wrap it in protective foam or place it in a confined space without good ventilation. Better quality ESCs can generally perform well above their rated limits with no apparent ill effects, but you should always size the ESC at least one step above your expectations for current load to be safe. I had, by ignorance, been running my Jeti 8 Amp ESC regularly at WOT (Wide Open Throttle) loads at 13.5 amps without ever hitting thermal overload or noticing excessive overheating. Lucky I guess, but a tough little bugger for sure.

Many ESCs have programmable features like Braking, Soft Start, “timing” functions, etc. These provide modelers with options to suit their preference in how the ESC controls the motor. Read the instructions that come with your ESC for detailed instructions on programming. Every brand of ESC has various different techniques to program these features.

Many ESC also have a low-battery warning system to notify the pilot when it’s time to land. This is provided so the pilot does not lose control of the aircraft by complete power loss, since the ESC powers both the controls and the motor. Various ESC controllers do this differently. Some make the motor surge, some beep, some shut off the motor and require pulling the throttle back to idle and then back up to restore motor power. Most reserve some juice for a controlled landing under limited power. Again, refer to the ESC instructions to understand how your particular ESC manages low-battery conditions.

Continued…