General:
A brushless motor controller or brushless ESC (Electronic Speed Control) is used to vary the speed of a brushless motor. These function as an interface between the motor and the battery. Controlled by the throttle signal from an RC receiver, the brushless ESC provides variable power to the motor allowing proportional speed adjustments. Unlike a brushed motor, power cannot be directly applied to a brushless motor. Instead, the speed control intelligently powers each phase of a brushless motor in sequence, causing it to rotate. Brushless speed controls have three motor wires, allowing them to connect to standard three phase brushless motors. A brushed speed control (with two motor wires) cannot be used to power a brushless motor.

Amp And Cell Rating:
Each manufacturer has many speed controller models available, most differing only by their amp rating. This is the maximum amount of current that they are able to continuously supply to a motor. The cell rating is the maximum number of cells that the speed control is rated for use with. Exceeding this may damage the speed control. The cell rating may specify both standard cells (NiMH and NiCD at 1.2V per cell) and lithium polymer cells (at 3.7V per cell). A speed control rated for 5-12 standard cells may be rated for 2-4 li-poly cells (4 li-poly cells put out roughly the same voltage as 12 standard cells).

Voltage Cut-off:
When using lithium polymer (li-poly) batteries, it is important that the speed control you use has a low voltage cut-off. This will limit how deeply the battery is allowed to discharge, and prevents it from being damaged. The voltage cut-off may be automatic (the speed control will detect how many cells are being used) or manual. For manual settings there may be hard (speed control shuts down when the limit is reached) and soft (speed control reduces power) cut-offs. The soft cut-off should be set at 3.3V per cell (9.9V total for a 3 cell pack), and the hard cut-off should be set at 3.0V per cell (9.0V total for a 3 cell pack).

Which Speed Control Goes With What Motor?:
Select a speed control with a continuous current rating greater than or equal to that of the motor you wish to use. This will ensure that the speed control is able to handle the power requirements of your motor. If you are using more than 3 or 4 li-poly cells, ensure that the speed controller is rated for this, or it may be advisable to move up to a high voltage version such as the Castle Creations Phoenix HV45, HV85, or HV110.