For an electric-powered model you must install the motor, ESC, and battery inside the aircraft and integrate it into your onboard RC system. The radio essentially operates the ESC, which operates the motor’s speed in flight.
Your biggest concern at the start with electric power is understanding and correctly charging the battery. A battery that is not fully charged is much like a fueled model with only a partial tank of fuel.
Motors
The ESC is probably the heart of the electric power system. The ESC in electric-powered flight takes the place of the throttle (or engine) servo used on a fueled model.
The ESC in this instance has two pairs of wires: a servo-type cable and a cable with a switch on the end, all exiting the case. Two wires, with APP connectors already attached, will plug into the motor wire connectors. Polarity is important, so it is red to red and black to black.
Two more wires will have APP connectors attached, and they will plug into the battery pack. The third cable has a servo cable connector on the end. That cable is plugged into the throttle port (usually the number-three position) on your RC receiver. The switch will be mounted on the side of the fuselage and must be manually turned on to activate the entire electric power system.
There are all kinds and sizes of ESCs on the hobby market. The one chosen for this project is the Jeti 110. The ESC will be rated for current; in this case it is 11 amps continuous operation. For our application we need 8-9 amps, so there is a margin of safety. If the rating wasn’t high enough, you could overheat and possibly burn out the ESC. The rating must also take into account the number of cells in the battery pack. The Jeti 110 can handle six to 10 cells. We will be using an eight-cell battery.
Many small ESCs (such as the Jeti 110) will contain what is called a “Battery Eliminator Circuit” (BEC). It will permit the main motor battery pack to also power the onboard RC system (receiver and servos) on a shared basis. This saves the weight of an extra airborne battery pack. It is also a convenience because this one battery is recharged for every flight.
In actual practice, the BEC has a special circuit that provides a regulated 5 volts to the RC system via that cable that is plugged into the receiver throttle port. When the battery gets down near 5 volts the circuit cuts off the motor, but it still provides the necessary power to operate the RC system so that you can safely land the model.
Most ESCs with this BEC feature (the Jeti 110 included) will allow you to briefly restart the motor after the first shutdown. You do this by moving the throttle stick on the transmitter all the way to idle, then back up. That resets the ESC and will allow a few more seconds of power so that you can line up on the runway for a safe landing.
Most modern ESCs (including the Jeti 110) employ “smart” circuitry via a microchip, which can add considerably to the safety of electric motor operation. Remember what I wrote earlier: when the battery is attached to the motor, it could start instantly. If you have the throttle stick at full or partial with the entire system plugged in, the motor and propeller could start turning.
The microchip in the ESC will sense anything other than a dead idle position and prevent the motor from starting. To start the motor you must physically move the transmitter throttle stick down to idle then go back up. The motor will then start, and its speed will be proportional to the control-stick position.
The Battery
The last item in the electric power package is the essential battery charger. There are many choices, simple and complex, available at varied prices. Kirk Massey’s favorite for a beginner is the Global (WattAge brand) PF-12 Park Flyer AC/DC peak-detect charger. The key words are “peak detect”!
Some of the simplest battery chargers come with just a rotary-crank type timer. You rotate the timer switch to 15-20 minutes and wait for the timer to run down. The trouble with this is that the charger can’t sense the amount of charge already in the battery. This can easily result in overcharging, which can cause excessive heat buildup in the battery. An overheated battery can quickly be ruined.
A peak-detect charger is essentially an automatic charger. All Nickel Cadmium (Ni-Cd) and NiMH batteries have a characteristic where the voltage applied during charging increases until the point of full charge (full capacity) is reached, at which point the voltage peaks then begins to drop off. At the peak, or slightly thereafter, the charge cuts off automatically.
Since this is a sensing cutoff and not a timed cutoff, only what is necessary to reach full charge is put into the battery. If your battery had residual charge in it, the charge period would be reduced accordingly.
The one thing you must do manually is tell the charger the amount of charge current required. For NiMH batteries it is suggested that you apply a charge current equal to two times the rated capacity of the battery. We refer to this as “2C.”
In this case the battery is rated at 1100 mAh (which is the same as saying 1.1 amp per hour). Mulitiply 2.0 by 1.1 amps, which equals 2.2 amps. This particular Global charger has a maximum charge current of 2.0 amps, so you would set the charger to that maximum current. At that approximate 2C charge rate, a fully depleted NiMH battery pack would take roughly 30 minutes to reach full charge.
Each battery will vary according to the number of cells, the type of the cells, and the capacity rating. You will pick up on this concept as you progress with electric power. For this first choice we’ve selected a charger that can’t overcharge the battery pack because its maximum current of 2.0 amps is close to what this battery requires.
When you purchase this or any charger, it is generally your responsibility to prepare a cable that will allow the charger to connect to your battery pack. Kirk Massey has prepared a cable with APP connectors to attach between the Global charger and our battery pack. Note the output connectors on the front of the Global charger. Press down on each connector, insert the wire, then release. Do that for the positive (red) and negative (black) connectors.
Later you might want to purchase a more sophisticated charger that has a higher current rating or can handle battery packs with more cells. (The Global is capable of handling four to 12 cells.)
There are several fully automatic chargers on the market. When you attach a battery to one for charging, it will sense all of the necessary parameters and set the charger accordingly. The concept involves a computer sensing system and has a menu that must be accessed for regular operation. These chargers work well, but they are more complicated to use than this basic Global unit and they cost much more.
It is typically a good idea to remove the battery pack from the model when charging. Immediately after a flight the battery may be quite warm–even hot. A basic rule is to never charge a hot battery. You should cool it off before attempting to recharge. Putting a hot battery in your soda cooler isn’t the right method. It will result in uneven temperatures throughout the pack.
The better approach is to buy a RadioShack 12-volt electric fan (part number 273-243). You can mount it at one end of a length of 3-inch-diameter PVC (polyvinyl chloride) plumbing pipe. Power the fan from your 12-volt car battery. Put your hot battery pack at the other end of the PVC tube. This will allow the air the fan blades generate to pass over the battery pack and cool it. Approximately five minutes in this tube will reduce the temperature to a safe level for charging.
This Global charger can be powered by 115VAC for indoor (shop) use or from 12 volts DC from your car battery. At the field, most of us just raise our car hoods and attach the charger input cables (alligator clips) to the battery terminals.
The polarity is important. Make sure that the red alligator clip goes to the car-battery positive (+) terminal and the black goes to the ground or negative (-) terminal. The Global charger has a built-in timer circuit that cuts off the charger after a 90-minute period. If you left the charger unattended and something went wrong, the charger would safely cut off.
That’s the full electric power system. Remember that this article has been prepared as a starting point for a rank beginner who is entering electric flight. If you are lucky to live near experienced electric modelers, by all means solicit their help; it can save you a great deal of time.