Over recent years there has been a major revolution in model motor technology with the advent of brushless motors. As the name suggests, these don’t rely on fixed brushes to transmit the power to the central armature. Rather they are made 'inside out' with the wire coils fixed around the inside of the motor casing and a permanent magnet rotating the shaft inside them. The power to energise the coils is transmitted by some very clever, fast-switching electronics outside the motor case. Because there are no brushes, these motors are much more efficient than their brushed cousins, so a small and light brushless motor will do the same job as a bigger, heavier brushed one. There are no brushes to replace and so the motors are virtually maintenance-free. They are, however, very hungry for power and so heavy-duty cable and batteries which can supply high currents are required (usually NiMH or LiPo types). They also have a couple of other limitations in that low-speed control is not yet as good as with the brushed types and there are only a few speed controllers available which will allow remote selection of forward and reverse. Because they have no commutator to create RF interference, brushless motors don’t require suppressor capacitors, which should please the ‘solder-phobes’!
Just to muddy the waters a little further, there are two types of brushless motor. Those where the outer casing of the motor is fixed to the mount and the shaft rotates within the casing are called 'Inrunners', while those which have a shaft fixed to the rotating outer case are 'Outrunners'. The latter type is more useful for model boats as they generally have higher torque and lower RPM than the former. In model boats the water-cooling of brushless motors is sometimes necessary; more frequently with the higher-revving Inrunners but occasionally where the load on an outrunner is relatively high. This is achieved by using the propeller to force cold water from the pond through a scoop just behind the propeller blades into a flexible tube. The water passes through this tube into a specially-made motor mount and conducts the excess heat away through a small exit outlet in the side of the hull. In many cases this cooling water also needs to pass through the speed controller, which will have tubes already fitted for the purpose, Photo 18
and Photo 19
At the moment the general practice seems to be to use brushless motors where speed is the main criteria for performance, with brushed motors still being by far the most popular for model workboats, warships and submarines, but like the man says, you pay your money and you take your choice! Just remember that you cannot run a brushless motor using a brushed-motor speed controller and vice versa.