Introduction

The Micro Reversible Electronic Speed Controller (ESC) is a small size bidirectional (reversible) electic motor speed controller. It was designed for small ship models which needs small power to run and the size avaiable for the ESC is very limited. It also can be useful for controlling auxilary motors like wench, creane movement, etc.

Even the small size of the ESC it has almost all of the features what are common in bigger ESC. It has arming function. When the ESC turned on it goes to standby state so the motor will not run even the throttle settings is not neutral. First the throttle stick must moved into netural position and after that the ESC goes into armed state where the motor speed can be controlled by throttle stick. The ESC also limits the acceleration of the motor in order to protect the motor, drivering gears, shaft, propellers and other parts of the drive train. It has protection against the overtemperature. In the case of overheating the power switching part the speed controller it goes into standby mode and stays there until the temperature drops below an acceptable limit. To elimintate the motor whistle (annoying noise from the electric motor) the ESC uses high switching frequency which is over the audible range so the motor runs smootly and silently only the normal motor nose can be heard. For the smooth motor control the speed range is divided into 256 points in both direction which gives very fine control over the motor speed. In the case of the radio signal loss the ESC stops the motor in order to avoid the damage the uncontrolled model (for this function you must be sure your receiver will stop sending servo pulses in the case of radio signal loss).

The battery eliminator circuit (BEC) which can supply servos and other circuit from a higher voltage battery was omitted  because of the small size of the ESC and low power supply requirement. This makes possible to run the ESC from 3V and above. For example if your motor also works from low voltage only four NiCd cells are enough to run the speed controller. Of course always be sure your receiver works from lower power supply. If you intend to use higher voltage 6-15V you will need an external battery eliminator circuit.

Even the circuit has some protection please be sure never violate the maximum voltage for any (circuit and motor) power supply. Never connect it to a power supply in reverse way and never short the motor wires. Any of these may damage the circuit.

The hardware itself is very simple contains only one microcontroller and few additional RC elements for power supply and signal filtering and two FET pair for power switching.

The firmware was written in ASM.