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Speed and Power

So what are they and how do they work?

First there was the mechanical variable-resistance speed controllers, operated by a standard servo, which controlled the speed of the motor by ‘bleeding off’ unwanted power.

A contact on the end of a wiper arm moved across a coil of resistive wire like a rheostat, this was very wasteful in terms of battery power.

The modern electronic speed controller comes in two distinct types, depending upon the motor, that’s brushless and brushed.

There are two distinct parts to the inside of an ESC; the logic circuitry and the power circuitry. The logic components are the ones which are connected to the receiver via the 3-wire lead with a plug on the end.

The purpose of the logic circuitry is to detect and decode the signal coming from the receiver and to switch the high-speed, high-current semiconductors in the power circuit which control the speed and direction of the motor. The ESC manufacturer will state in the technical information the range of main motor battery voltages with which the ESC will cope, along with what should be a value for the maximum motor current (in Amps) which the ESC will handle under continuous operation. You should be guided by those two values when choosing your ESC, after first ascertaining the working voltage of the motor and its current consumption under load as described earlier.

The power circuit connections of an ESC will always comprise a pair of thick battery cables. These are usually made in red and black, for positive and negative connections respectively. There will also be a pair of cables to connect with the motor terminals, often in blue and yellow, but be careful and check your instruction leaflet first. Brushless motor ESC’s have three motor wires. It doesn’t matter which way round you connect the motor wires to the motor, BUT the battery connections should NEVER be reversed. If you wish to reverse the direction in which the motor is rotating then just swap over the two wires from the ESC to the motor. For brushless motors swap over any two of the three motor wires.

The only other variable is whether or not the ESC contains a battery eliminator circuit. If it does, then you must NOT connect an additional power supply to the receiver. Some BEC-equipped ESC’s have a small slide-switch on a pair of thin wire leads. This usually controls the onward power from the internal BEC voltage regulator to the rest of the radio system and therefore serves as a radio ON/OFF switch. It does not control the power supply from the battery to the ESC, so I would recommend also fitting an addition high-current switch in the positive lead from the main battery to the ESC unless you are in the habit of disconnecting the battery physically each time you remove the model from the water. If you do disable the BEC for any reason, then leave the little switch in its ON position or you may find that the ESC doesn’t work. Check the ESC Instructions if this happens.

Always follow the manufactures instructions to avoid possible damage to the ESC unit.

This is just a basic guide to ESC, and I would recommend further research as to which is the best type for your model boat.