Frequently Asked Questions for Electrics

 What is the Low-Down on Electric R/C ?

Over the past 5-10 years, Electric model aircraft have gained a lot of momentum in the R/C market due to advances in technology (Lithium Polymer batteries, brushless motors, electronic speed controllers, etc.) combined with a drastic reduction in the cost of the equipment. Starting costs on a fully functional ready-to-fly electric R/C helicopter or plane can be as low as $100 (or less).

 Another advantage of electric R/C aircraft is size – smaller models (often referred to as “micro” R/C aircraft) can weigh as little as 1-2 oz. and can be safely flown indoors. Additionally, there is no fuel mess, glow plugs, or starters required in your field box when you head out for a day of flying with your electric R/C aircraft – only the model, battery, and radio equipment are required.

 Many electric models do not require a separate receiver (Rx) battery pack, one battery pack can power the entire model – this includes the motor, servos, and the radio receiver. This further reduces the need for additional components required to run your R/C aircraft.

 Which electric aircraft model is best for a beginner?

There are a lot of good beginner choices for both helicopters and planes. The best models for beginners are generally those that require the least amount of investment (Bind ‘N Fly or Ready-to-Fly models are a good example), so that in a crash the model is neither expensive nor time-consuming to repair or replace. Smaller models might be less expensive, but not necessarily easier to fly, in fact, most small/micro models are rather difficult to fly compared to medium-sized or larger models which are more stable in flight.

 For planes, “park flyers” and powered gliders are often the best for beginners. These are planes that are fully functional (ailerons, elevators, rudder, etc.), but fly smoothly at more docile speeds. Many park flyers are available Ready-To-Fly, so build and assembly time are minimal to nonexistent.

 Some recommended electric beginner planes include:

Multiplex Easy Star, Park Zone J-3 Cub RTF, Park Zone Slo-V RTF, and the HobbyZone Super Cub LP, to name a few.

 This web article provides some additional examples with more details:

 http://www.rc-airplane-world.com/beginner-rc-airplanes.html

 For helicopters, coaxial electric helicopters (dual counter-rotating rotor blades) are the best for a beginner. While they do take some practice to fly, coaxial helicopters are inherently more stable and very forgiving while in flight. The E-Flite Blade CX is a popular coaxial model. This article provides additional details:

 http://www.rc-airplane-world.com/coaxial-rc-helicopters.html

 After the basic methods of flight are mastered on an electric coaxial R/C helicopter model, the next step is to move to fixed pitch and finally collective pitch electric R/C helicopters.

 What Equipment will I need for my Model Aircraft?  

If you purchase a RTF (ready-to-fly) model, most of the components listed below will have already been configured/included for you by the manufacturer, ParkZone’s Bind ‘n Fly (BNF) models are an example. However, when building a new electric R/C aircraft where the electronics have not been provided, the following 4 items will need to be considered at some point during or after your build.

1. Battery:

Lithium Polymer (LiPo) is the best and most reasonably-priced option available currently, and the main reason Electric R/C has gained so much popularity over the years. LiPo battery packs are light-weight, available in many shapes and sizes, charge in relatively short time frames, and last for hundreds of cycles (charges and discharges) if treated properly.

LiPo battery pack prices depend on capacity (given in Amp Hours or Milliamp hours – Ah/mAh), discharge rating (denoted by “C”, i.e. 45C), and cell count (denoted by “S”, 3S is a 3-cell battery pack). Some simple math can help you determine how much power a battery pack is capable of producing. The formula for max power output of a battery is:

C * Ah = Max Amp Output

(Discharge * Capacity in Amp Hours)

So, a 45C battery with a 2200mAh capacity (2200mAh = 2.2Ah) is: 45 * 2.2 = 99 Amps max power output. This formula is very useful in determining which battery capacity/discharge is needed based on the weight and power demands of the model being built.

Other R/C battery choices include A123 (aka LiFe), NiCd, NiMH, and Lead Acid. However, these other battery types are much heavier and generally not a good choice for R/C aircraft where minimizing weight is critical.

A more detailed and technical guide to understanding Lithium Polymer batteries can be found on Wikipedia: http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery

2. Battery Charger:

Multi-purpose balance chargers capable of charging LiPo, LiFe (A123), NiCd, NiMH, and lead acid batteries are the best investment for a battery charger because they handle all the battery types as well as properly balance-charging a LiPo battery pack. Balance charging is best-practice for LiPo battery packs as each cell in the pack must hold the same voltage for longest life and safest use. LiPo batteries should only be balance-charged, not charged like traditional NiCd where power is just pumped into the entire battery at once.

There are a wide variety of balance chargers available from various manufacturers. These manufacturers include: ThunderPower, Bantam, Hyperion, E-Flite, and numerous off-brand models. Before choosing your charger, make sure it is capable of charging the number of cells of your largest LiPo pack. If you use 6S battery packs (6-cell), make sure the charger is capable of charging a 6S LiPo pack. Balance chargers range in price from $50-$150+ depending on make/model.

Safety Tip: NEVER charge a LiPo battery with a NiCd or NiMH-only battery charger, a Lithium-compatible charger is a must; do not exceed the charge power or voltage of the battery as recommended by the manufacturer.

Note: Many of the popular Lithium/multi-battery balance chargers require a DC power source, so an AC/DC power converter or adapter may become necessary, depending on the charger model you decide to purchase.

3. Motor:

The question of which motor to choose should no longer be brushed vs. brushless. Now that brushless motors are widely available and very reasonably-priced, brushed electric motors are a thing of the past. Brushless motors have a very long life-span and provide tremendous power at high efficiencies, unlike brushed motors which are heavy, wear rather quickly, and are relatively inefficient.

There are two types of brushless motors: inrunner and outrunner. This article is quite informative and explains the differences between brushed and brushless motors, as well as inrunner vs. outrunner (and pro’s and con’s of each):

http://www.hooked-on-rc-airplanes.com/brushless-rc-motors.html

Bottom line – most electric planes and helicopters use outrunner brushless motors, however, inrunners are still preferred for some types of aircraft.  

Determining which motor to use in a model aircraft is often an easy task – the manufacturer will generally provide specifications on which motor to use, often based on Kv (RPMs per Volt), weight, and total power output of the motor based on the prop or rotor size being used with the aircraft. The staff at Field’s Hobby (in Cheektowaga, NY) can help recommend motors based on your type of model aircraft.

4. Electronic Speed Controller (ESC):

Speed controllers (sometimes referred to as “the escape” or ESC) control the electrical pulses and power traveling from the battery to the motor based on throttle input. The higher the throttle, the more power that the ESC allows to flow into the motor, resulting in higher RPMs (speed) of the motor. The ESC is the “brains” of the electric model aircraft; most modern brushless ESC’s monitor battery cell voltage, and automatically cut power to the motor when a battery pack is discharged below the recommended voltage level. ESC’s will also cut power to the motor in the case of radio signal loss, ensuring that the model cannot continue flying indefinitely, preventing the model from flying out of sight and becoming dangerous to bystanders.

ESC’s are rated based on Amperage, which is why the battery formula mentioned previously (Discharge (C) * Capacity (Ah) = Amp output) is important for determining which ESC to buy for your model. Motor manufacturers generally give the max power (Amp or Watt) rating of a particular motor, which is also useful in determining which ESC to buy. If your motor/battery combination is capable of drawing 40 Amps at max throttle, an ESC rated for 40 Amps (or above) is required. It’s generally best practice to buy the highest Amp-rated ESC that fits your budget as well as staying within the ideal flying weight of the model aircraft. The higher the Amp rating of an ESC, the heavier it will weigh. It would not make sense to drop an 80-Amp ESC into a 2.5 oz. indoor model that only draws 5-10 Amps at full throttle, chances are the ESC would weigh more than the entire weight of the model (with battery installed).

Popular ESC manufacturers include Castle Creations, E-Flite, Hacker, Scorpion, and Jeti.

What Skills do I need to build my own Electric Model Aircraft?

In addition to having a good basic understanding of how R/C aircraft are built and operated, some basic soldering knowledge or soldering experience is a big plus. Often, modelers will need to have connectors soldered to their batteries, ESC’s, or motors, because the connectors are usually not preinstalled by the manufacturer. Field’s Hobby provides soldering services for a small fee, just bring your components and connectors into the shop (or purchase the connectors at Field’s), and their knowledgeable staff can handle the soldering for you.

How can I achieve the best Power to Weight ratio for my Electric Model Aircraft?

This is the most important factor to consider when building any R/C model, and under or over powered model can be dangerous to fly. Ensure that enough power is provided to maintain flight without over-stressing any one of the individual electronic components (battery, motor, and ESC). A simple rule is the Watts per Ounce formula. The general recommendation is 10W (Watts = Volts * Amps) per ounce to maintain flight; if an aircraft weighs 20 oz, it will need at least 200W of power for adequate flight performance. This formula should be considered when purchasing your electronic components for your model – battery, motor, and ESC. In most cases, the manufacturer of the model aircraft will provide a recommendation for all electronic components, you may choose any brand of battery, motor, and ESC that best suit your model per the manufacturer’s recommendations.