The range of fast motors is staggering and choosing the “right” motor is a highly debated subject.
I am not going to go into to much detail at this stage, as there’s brushed and brushless motors and that a subject for another post.
Most sports boat kits use 540, 550 and 750 sized motors or SPEED 500, 600 & 700 motors according to GRAUPNER numbering.
You will see these motors and others used in various kits, and these motors are from the cheaper end of the market but are good enough for most sports boats and club racing.
Whichever motor you choose is not the most important consideration, it’s the motor / running gear alignment that’s much more crucial. In every case the motor to prop shaft or shafts MUST line up correctly. Good alignment will mean less load on the motor therefore less current drain, enabling higher speeds. Bad alignment could damage the motor, running gear bearings, and overload the speed controller or just damage the boat. We need to achieve a perfectly straight continuation of the motor shaft down through the coupling and prop shaft to the propeller.
Alignment is purely a matter of the builders skill but even a novice can do a good job it just takes time to get it right.
In direct drive boats, i.e. motor in-line with a solid prop shaft, some sort of flexible or universal coupling must be used to join the motor to shaft. The coupling compensates for any slight changes in alignment that occur as the motor load varies. There are lots of different types of coupling but the plastic and brass couplings are the most popular and provide good service.
In all cases the running gear should always be free turning and quiet. If it’s easy to turn the running gear in your fingers and it makes hardly any noise, it indicates a good installation. Always check that the coupling is secure before running your boat. If it’s seems to wearing quickly during the boats life your alignment is out and needs to be corrected, a coupling “should” not wear out in most normal situations.
Most low cost 540 and 550 motors have sealed cans so cleaning or replacing worn brushes is difficult if not impossible, try meths on a cotton bud through the side cooling slots and turn over by hand.
I would recommend that all motors need SMALL drop of oil on the shaft bearings from time to time. The armature’s copper commutator also needs cleaning, model shops sell cleaning sticks for this which makes the job easier.
I use the MFA range of motors for most of my larger models, with the odd 540 or 550 motors when in smaller boats for higher speed.
This is just a basic guide to motors, and I would recommend further research as to which is the best type for your model boat.