By The Numbers: LiFe batteries

Lithium Iron Phosphate (aka LiFe, LiFePo, LiFePo4) batteries are most often used in RCLand for transmitters.  They're safer than LiPo, since they don't emit oxygen during rapid breakdown leading to combustion.  Lots of chemical detail on wikipedia.

Here's the model that fits into the Turnigy 9X transmitter.  Use the servo-style connector to plug it in.  Note that there are two ways to plug it in: only one of them works; the other doesn't do anything.

Charge Levels

 1S   3S

3.3   9.9  nominal voltage

2.8   8.4  minimal discharge

3.6  10.8  maximum voltage

Charging

You need to set your charge into LiFe mode.  Don't charge in LiPo mode. Bruce has a video here that explains how to do this on a standard 4-button charger. Here's the tldr for a typical 1500 mAh 3S:

Save Data / 01 / LiFe / 9.9 / 1500 / (hold start) / 1.0 / 9.9 / (hold start)
Save Data / pgm number / LiFe / voltage / mah / (hold start) / charge current / voltage / (hold start)

LiPo Battery Voltage numbers

Some handy voltage numbers.


cells                   1S      2S      3S      4S      5S      6s
nominal voltage         3.7     7.4     11.1    14.8    18.5    22.2
absolute low voltage    3.0     6.0     9.0     12.0    15.0    18.0    
low voltage warning     3.3     6.6     9.9     13.2    16.5    19.8
maximum voltage         4.2     8.4     12.6    16.8    21.0    25.2
storage voltage         3.8     7.6     11.4    15.2    19.0    22.8

By The Numbers: Brushless Motors

Brushless motors have lots of numbers associated with them.  Let's use the popular TowerPro 2408-21 as an example.  It's very well documented.  Here's the HobbyKing, TowerPro, and TowerPro Motor Spec pages.





Most Important Numbers

• Kv -- measured in RPM, shows the maximum rotational speed per volt of input (bigger number = faster spin = more power required).
• weight -- typically measured in grams.
• max current -- measured in amps.  The maximum current draw this motor can handle for an extended period of time (important for picking your ESC.  The ESC Amps should be larger than this number).
• max loaded current (60s) --measured in Amps, and usually given with a timeframe (60 seconds is common.)  The maximum current draw the motor can take for a short period of time without burning up.

Other Numbers

• Battery - number of cells
• dimension - the physical size
• shaft diameter - more powerful motors need bigger, stronger shafts.  you need to know this number if you buy a prop saver. 3mm is a common value.
• poles, magnets -- not sure why these are important, maybe highter quality motors have more?
  

Thrust Calculation
(still in progress)

Relationship of ESC numbers to Motor Numbers

• ESC Amp number must be greater than motor Amp number, or you will burn up you ESC by pulling too much electricity through the circuit.

"Runner" Configuration

Brushless motors are either inrunner or outrunner. The Towerpro motor above is an outrunner.

• inrunner -- the motor is stationary and the motor shaft spins
• outrunner -- the motor shaft is stationary and the motor body spins

Motor Equivalency

If you need to see how equivalent two motors are, the two most important numbers to match are

• Kv -- they should be close to the same power output
• Weight - they should weigh similarly

By The Numbers: ESC

The ESC (electronic speed controller) is used to control  the speed of a brushless motor.  It usually has a BEC ("battery elimination circuit") to provide power to servos and the other receiver outputs.

• Continuous Current -- how much current can pass through the ESC on a sustained basis.
• Burst Current -- how much current can pass through the ESC for a short "burst" of time (usually 60 seconds).  If you exceed this time, you will probably burn up the ESC.
• BEC (battery elimination circuit) -- How much power is available to the servo and other receiver outputs.
• Cells-- the voltage and type of battery supported.
• Weight: QED
• Size: QED

Wiring:

• two input wires from  the battery
• three output wires to the motor
• three-wire bundle to the receiver.  two wires power the receiver (including passing power to the receiver outputs), one wire is the control wire receiving the throttle control signal.

ESC Programmer: some ESCs can be programmed.  This can be done via the receiver (by "clicking"  through entries using the joystick) or more easily with an ESC programming card ("no more black magic throttle stick controls!").  Typical  programmable values are:

• brake -- on/off.  stops the motor immediately when throttle is cut, used for feathering props.
• battery type -- battery voltage, or "auto".
• cutoff type -- gradually reduce or immediately shut off power when the voltage threshold is reached.
• cutoff voltage -- 2.6V, 2.85V, or 3.1V per cell.
• start mode -- normal, soft, very soft.  helis use soft, planes use normal.
• timing mode -- low, medium, high.
• music -- for some inexplicable reason, you can program the esc to play different songs at startup.

By The Numbers: Batteries

LiPo Batteries.

• Configuration: How many cells the battery has. (1S, 2S, 3S)
  
• Capacity : How much electricity the battery holds. (500 mAh, 1000 mAh, 2200 mAh)
• Constant discharge: How fast the electricity can flow from the battery. (15C, 25C, 35-45C)
• Burst rate: A peak value that the battery can discharge for a short period of time.  (37C ,15sec)
• Pack size: three dimensions, HxWxL
  
• Weight: in these modern times, always expressed in grams.
• Charge Rate: how high of a current at which the battery can be charged (1C, 5C)

Notes.

"C" rate: This is the amount of power that can be pushed out of the battery at any particular instant in time. It is a ratio of the Capacity.  a 500 mAh battery discharging at 15C will be discharging at 750 mA. (500 * 15 = 750)
Lots of details here.

Voltage:  A single lipo cell will have a voltage range of 3.0V - 4.2V. The "nominal" voltage (how it's typically referred to) is 3.7V. If the cell goes below 3.0V, it won't be able to be recharged.  Most people recommend not letting a cell go below 3.2 volts so that you'll have a bit of safety margin.

So, a 3S battery will have 3 cells, a nominal voltage of 11.1V, and a voltage range of 9V - 12.6V (the nominal values multiplied by 3.

Your discharge rate requirements will be defined by your motor and ESC combination.  Models with high instantaneous power demands (helis, stunt 3D flying) will have higher discharge requirements.  Models with low instantaneous power demands (gliders, trainers) will have lower requirements.  Higher discharge rates usually mean the batteries will be heavier and more expensive.

Example: http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9312

• Configuration : 2S 7.4v
• Capacity : 2150mAh
• Constant discharge: 25C
• Burst rate: 37C (15sec)
• Pack size: 113x33x16mm
• Weight : 129g
• Charge rate not specified, so we assume 1C

By The Numbers: Props

Propellers have two numbers:

• length.
  
• the pitch. How far the prop would spiral forward in one rotation.

This illustration is from hobby king. X and Y are length and pitch.

By The Numbers: Servos

• Dimension: height, weight, length.
• Weight: and how much it weighs.
  
• Operating Voltage: electrical input range. for planes, this is almost always 4.5-6.0 volts.
  
• Operating Speed: how fast the servo motor turns. this measured in "seconds to rotate 60 degrees." often, there are two measurements, one for 4.5 volts (lower) and one for 6.0 volts. Be careful when there's only one number given, to make sure which voltage is being reported.
• Stall Torque: How hard the servoc can twist. At the given number, the servo will stall. The measurement is how much force is done from a particular arm radius. Like speed, there are often two numbers specified, for 4.5 and 6.0 volts.

Two other important bits:

• MG usually indicates "metal gear"
• Digital servos provide faster response, tighter accuracy, and higher "standing" torque at the cost of increased power consumption and a high-pitched squeal when operating.
  
• For small park fliers and foamies, the standard 9g and 5g servos are fine, e.g. the HTX-500 and HTX-900.

Example: http://www.superflyrc.com/Power-HD-HD-2216MG_p_51.html

• Dimension: 22.8x12x29.4mm
• Weight: 15.8g
• Operating Voltage: 4.5 - 6.0V
• Operating Speed: 0.13sec/60°at 6.0V
• Stall Torque: 54.12oz-in @ 6.0V (3.9kg-cm)