ESCs - AN OVERVIEW

In simple terms, these units work by rapidly switching the battery voltage to the motor on and off so that on average the motor sees a voltage proportional to the ratio of the 'on' to 'off' times. The switching rate is fast enough so the motor can't speed up or slow down during the 'on' and 'off' periods and just keeps to a steady speed.

There are low frequency and high frequency switching types which have their pros and cons. Low frequency units give better low speed control (the motor receives big but infrequent 'kicks' which break the stiction and get it moving) but are more lossy at high speed (larger peak to peak current excursions around the average so resistive losses in the motor and controller are higher). Also the motor may sound quite rough and growly at start-up.

For precisely the converse reasons, high frequency units are more efficient at high speed but have poorer low speed control. Generally the motor sounds quieter, though you may hear a 'singing' sound as it starts. The more recent Electronize units offer a variable frequency mode to get the best of both worlds.

Some units (eg Electronize) use a single switching transistor (FET) - or sometimes two or more devices in parallel, but they effectively just make a better single device - and invoke reverse operation with a double-pole change-over relay to swap the motor leads over. The controller chip is usually smart enough to only allow the relay to operate at zero motor speed (the zero speed condition being internally forced if the stick is rapidly slammed from forward to reverse) This way the relay contacts only 'carry' motor current rather than 'switch' it so their life and current rating is considerably increased.

When using a relay reversing ESC, care should be taken to ensure that the relay is de-energised during forward operation so the current drain of its coil is only suffered during (infrequent) reverse operation.

Other units like Mtronics Viper use four switching transistors (FETs) in an 'H' bridge configuration to get forward and reverse operation without a relay. This usually results in a smaller unit but there are now two sets of FET conduction/switching losses to deal with and the potential for attempted suicide if a forward and reverse FET get 'on' at the same time (ie a dead short across the battery). Relay reversing types always have a motor protecting the FET (unless it's stalled!)

Generally speaking the FETs used have huge current ratings in comparison to the quoted controller capability, but if their heatsinking is inadequate (by accident or design) they will quite happily fry at quite modest currents. So it's worth checking on Electronize units that the power FET mounting screws (middle of the underside plate) haven't worked loose.