Brushed motor manufacturers classify their products by number of poles, slots and number of turns. In this article we analyze these components one by one and the influence they have on the functioning of the brushed motor.
Description of the components
Number of Poles
Poles are are the permanent magnets, tipically 2 or 4. They are always less than the number of slots.
Number of slots
It is the number of blades present on the motor commutator and is always an odd number, 3 or 5. Each blade is connected to a winding of the armature, so the number of slots also corresponds to the number of windings.
Number of turns
A turn is one turn of electrical wire around the each armature winding. All armature windings have the same number of turns.
Influence of the number of turns
Like all conductors, the wire used for windings has electrical resistance.
Considering two identical motors with different numbers of turns, the motor that has more turns drains less current because of the higher internal resistance due to the larger use of conductor.
In many cases, to recover the dimensions of the greater number of turns, a conductive wire with a smaller section is also used, which further increases the overall electrical resistance.
The result is that a motor with more turns offers less power, less torque and lower RPM, as confirmed by this chart of Surpass Hobby.
Influence of the number of slots
The same happens in two identical motors of different number of slots; the motor with more slots has more electrical wire because the coils are wound on 5 windings instead of 3; in this case, considering the same number of coils, a motor with a higher number of slots offers less power, less torque and a lower number of RPM.
Advantages of motors with multiple slots and poles
The number of turns affects the performance of the motor, the number of slots and poles influences the smoothness characteristics.
When more slots are used, the commutations for each revolution of the motor increases, and more poles make the magnetic field more stable. A 5-slot 4-pole motor is a veryfluid and linear motor compared to a 3-slot/2-pole motor.
Conclusions
What we discussed allows us to conclude that a brushed motor with a high number of poles, slots and turns has appropriate characteristics for scaler and crawler applications, where power control and smooth running at low speed are crucial factors .
For faster model cars, however, these aspects are not relevant and our advice is to continue using the most popular and classic 2-pole 3-slot motors, which are also less prone to sparking and wear of the brushes and therefore of the commutator.
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