Electrics -Glossary

Like most new fields there is some new and occasionally complex terminology used in this area. In some cases it is not that the words are new but rather that there are more specialised meanings for common words. I have gathered together what I can below.

(Words in CAPITALS in the definitions are also in this glossary)

Amps

Measurement of CURRENT.

Battery (or Battery PACK)

A number of CELLS connected together to form a power source. The battery used for the main in-flight power source is normally constructed from rechargeable cells and is often known as a "pack" to distinguish it from the large car type lead-acid battery used to drive the CHARGER. I will normally use PACK to mean a flight battery and battery to mean a 12V car/leisure battery.

BEC

Battery Elimination Circuit. A circuit, usually contained within the speed controller or ESC, which allows the radio control receiver to be run from the motor battery. This saves carrying the extra weight of a separate receiver battery. The 5 volts needed for the receiver is supplied by reducing the input voltage. Because of this most ESCs only support BEC up to a certain number of cells (and therefore a certain voltage input) and for a specified number of servos. Over these the heat produced by the voltage reduction may fry the controller.

Brushless Motor

Modern, expensive and efficient. Also will work over a greater range of voltages and currents than a standard brushed motor.

C (charging rates)

Charging (and sometimes discharge) rates for cells are often talked about in terms of 'C'. A charging rate of C is that which will fully charge a cell in 1 hour. You can work this out from capacity. In fact it's the same number but just expressed in mA. E.g. for a 2000 mAH cell the C rate is 2000 mA i.e. 2A. The inital charge for a battery and the "normal" slow charge is at the C/10 rate. For the 2000 mAH cell this will be 200 mA (2000 divided by 10).

Can Motor

Another name of a FERRITE MOTOR

Capacity

Usually battery or cell capacity. It is measured in Amp Hours (AH) or more commonly milliAmp Hours (mAH). 1 AH = 1000 mAH = the ability to deliver a CURRENT of 1 Amp for 1 Hour, or 10 Amps for 6 minutes (1/10th of an hour), or 30 Amps for 2 minutes etc. Note that this is not related to voltage. It a characteristic of the CELL type. To get greater VOLTAGE you add more CELLS.

Cell

All rechargeable cells provide a nominal fixed voltage (for NiCad, NiMH this is 1.2V). Cells are connected together into PACKS to provide the voltage required for the task in hand

Charger

Device used to recharge PACKs, usually from a 12V car/leisure type battery. These come in a wide range of prices and specifications. The main things to look for are the number of cells they will charge and the maximum current they will deliver. You will find a price jump from chargers which charge up to 7 cells and those over. That's because to charge more than 7 cells from a 12V battery requires special circuitry to increase the available voltage.

Cobalt Motor

This term is generally used for brushed (conventional) motors with are earth magnets. Some of these (Astro) actually use cobalt as the brush material but there are other materials used. Regardless of the precise material these are all commonly, if inaccurately, called cobalt motors.

Current

The flow of electricity. Measured in AMPS (symbol A)

ESC

Elecronic Speed Control. This device is the equivalent of a throttle for electric motors. It controls the power into the motor. Many ESCs are also fitted with other facilities like BEC (see above), a brake (to stop the motor windmilling and allow folding propellers to close properly)

Energy Density

Characteristic of a cell. It is basically a measurement of how much CAPACITY you get for each unit weight. Since the cells are usually a high percentage of our total weight the higher this is the better. If you could get a 2000 mAH cell that weighs only half the conventional ones you would save a lot of weigh from the plane.

Ferrite Motor

Brushed (conventional) type of motor with low cost ferric oxide magnets.

Folder

Folding propeller. When the motor is not running the prop blades fold alongside the fuselage for lower drag (and you don't break so many blades on landing). Typically used with powered gliders.

Internal Impedance

This is the main characteristic of a CELL which limits the maximum current you can get out of it. So far NiCds have by far the lowest internal impedance available.

Lithium cells

Several different battery technologies are based on Lithium. E.g. Lithium Ion, Lithium Metal. These rechargeable cells have very high ENERGY DENSITY (and give 3V per cell not 1.2V). However they have very low maximum DISCHARGE rates, typically less than 1A. They also need to be charged very very carefully. They are being used for some very lightweight indoor or slow fly planes but that's all.

Mabushi

Largest manufacturer of standard can motors in the world. Many of the motors sold for electric flight e.g. Graupner Speed series are actually made by Mabuchi.

NiCd or NiCad

Type of rechargeable CELL. Short for Nickel Cadmium. At the time of writing these are the best cells for our purposes as versions of them are available which provide the high discharge CURRENTs that we need together with the ability to be recharged quickly.

NiMH

Type of rechargeable CELL. Short for Nickel Metal Hydride. These have a higher ENERGY DENSITY than NiCd cells but usually a higher INTERNAL IMPEDANCE so give lower maximum CURRENT. They do not like being charged very fast. These cells are improving though. At the time of writing (early 1999) sub-C cells are available which are good for 2400 mAH and up to 20A draw.

Power

Slimer

Rather rude term for I/C or fuel powered aircraft. Pretty accurate but no way to avoid an argument down at the flying field.

Soft start

Some electronic switches will ramp the current up over a small time (often less than a second) when you switch on. This greatly helps to reduce wear and tear on motors and particularly gearboxes. Some ESCs also claim this feature though it only really does anything if you slam the throttle wide open from zero.

Volt/Voltage

Watts

Measurement of power. Electrical power is equal to VOLTS times AMPS.