HOW DOES A WHEEL MOTOR WORK?


Today the wheel motor, also called the hub motor, has become a simple and essential means of electrifying a large number of light vehicles (bicycles, motorcycles, scooters, scooters, etc.). In fact, this solution, fixed directly to the frame, does not require the readjustment of the transmission. This is a "brushless" motor, that is to say brushless motors.

There are 2 types of wheel motors: the direct drive motor and the so-called reduction motor.

In this article, we will focus on these 2 engines, different in their design, each of which has interesting advantages but which can also present some disadvantages for certain types of use.

These 2 engines are installed on a vehicle in the same way. In most cases, they are used for the bicycle so let's take as an example a mounting on this means of transport (diagram below).

These hub motors have the option of being installed on the rear wheel or on the front wheel. Whether direct drive or reduced, the wheel motor radiates the same way on the rim of the bicycle.

Now that we have seen the principle of mounting a wheel motor, let's go into more detail on the characteristics of these 2 motors.



Direct drive brushless motor

These current variations in the winding will continually modify the polarity of the poles of the stator which will cause electromagnetic forces which will make the rotor turn via its magnets and therefore the wheel of the bicycle.

As its name suggests, the brushless direct drive motor is a motor that sends the power of its rotor directly back to the wheel of the bike, without going through gears. The 3 motor phases, coming from the controller, supply the stator winding with alternating current.

The motor flanges are then screwed on each side.



Advantages/Disadvantages of the Direct Drive motor compared to the reduction gear

+ :

  • The design is simpler, the number of parts in the engine is small. This therefore increases its reliability by reducing the number of possible failures. In addition, it makes it less noisy.
  • The regen: As this motor does not have freewheel type gears (between the stator and the rotor), it allows the regenerative brake to be used. Depending on the controller with which the motor is associated, it can be used to recharge the battery during these regen phases. This can be interesting on a route with a lot of descents where the motor acts as an engine brake and at the same time allows the battery to be recharged.
  • Its price is lower. Fewer parts therefore less expensive to produce.

– :

  • The diameter of the motor is larger. Since this motor does not have gears to leverage its power, it needs to be bigger because its power comes directly from the electromagnetic forces of the stator magnets applied to the rotor magnets.
  • The mass is more important. This motor is large and robust, so it is heavier than a reduced motor. Its weight/power ratio is worse than that of a reduced motor.
  • The rolling resistance is greater due to the absence of a freewheel. This makes it harder to pedal when the engine is not running.


Reduced type brushless motor

The reduced motor, on the other hand, has a planetary gear to turn the crankcase, and therefore the wheel. This solution makes it possible, for a smaller motor and therefore with weaker electromagnetic forces, to multiply its rotor output power in order to have a much higher motor power. For the 250W motor sold from OZO, the reduction ratio is 1: 4.4. For all other OZO reduction motors (power> 250W), the ratio is 1: 5.

The rotation of the rotor by the stator works exactly on the same principle as for the direct drive motor.

So first, the stator, supplied with alternating current, spins the rotor. Then, a small pinion fixed to the rotor comes to put the planetary in rotation (diagram below).


Puis le planétaire vient mettre en rotation le carter moteur, et donc la roue, via une denture intérieure intégrée dans le carter.

La vue éclatée du moteur réducté vous permettra d’y voir plus clair.


Advantages/Disadvantages of the Direct Drive motor compared to the reduction gear

Les + :

  • The motor is smaller. This motor uses gears to multiply the rotor output power. It therefore has a smaller diameter although it is slightly larger.
  • It is lighter at equivalent power. Its weight/power ratio is therefore better.
  • It has less rolling resistance. The sun gear acts as a freewheel when pedaling, so it is easier to pedal if the motor is not functional.

Les – :

  • It has no regenerative brake. Who says freewheel says no motor brake.
  • Its design is more complex. This motor has gears, and therefore more parts compared to the direct drive, which are potentially subject to greater risk of wear. These extra parts make the engine a little louder.
  • The price is higher. More parts therefore more expensive to produce.

Conclusion

Now that you can see more clearly about these 2 engines, you are able to understand that these 2 engines are complementary and that your choice will depend on your type of use.


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