Electric Bike Motor Types
- An electric bike system generally consists of a similar set of components, primarily the motor, controller and battery
- The motor can be constructed in different ways and mounted in various locations; both these factors will impact the performance of the bike and give different advantages
Electric bike systems
typically consist of the follow components mounted on a bike.
- Battery, to provide power. Electric
bike batteries are typically 36 volt lithium (Li) ion batteries, and need to
have sufficient capacity (range) and power output - refer to battery notes for
to drive the bike. This can be mounted in different ways as discussed below. In
all cases however, riding an electric bike a 'joint effort': the pedals and
chain work to drive the bike in the usual way for a bike, with the motor
providing additional power on demand
which sits between the battery and the motor and regulates the system. The
controller needs to be appropriate to the voltage and current of a given system
and can limit performance otherwise. In some systems the controller is in a
separate box; in some it is integrated into the motor unit, which generally
gives a neater look with less visible wiring
components required to operate the system. these may include some or all of the
/ pedal sensor, which activates the motor when the pedals are turned. This may
be referred to as pedal assist (PAS) i.e. activation of the motor via the
pedals rather than a throttle
(thumb, half twist or full twist), which activates the motor progressively
/ programming unit: while the controller runs the system, most setups will have
an additional unit mounted on the handlebars which provides system information
and may allow some degree of programming system parameters
(or variants); devices which cut the motor power automatically when a brake is
applied or other action taken. Systems will generally run without these, but installation
of at least one is recommended as good practice
Optionally, secondary systems that run off the battery may be added as required e.g. lighting.
Finally a charger: this is typically not mounted on the bike, but is a separate unit that plugs into the mains to charge the battery in between use
The motor consists of a set of coils of copper wire mounted
within a set of magnets (as per photo - motor cover removed to show the copper
coils and the ring of magnets circling them, with a small gap to allow rotation
of the motor). When an electrical current from the battery flows through the
coils, the magnetic field generates a force on the coils, which causes a rotor
to turn. This is the basis of all electric bike propulsion. Note that the power
is transferred via the magnetic field rather than by physical contact, so a
simple motor does not need to have moving parts in contact and can be extremely
robust as a result. Electric bike motors are general brushless construction,
usually with Hall sensors (both being aspects of motor construction that give
greater efficiency, typically up to 80% or more at optimum motor speed).
Types of Motor
Although the propulsion mechanism is the same, there are two types of construction of motor as follows.
name can be misleading since, generally, neither type contains multiple gears
in the sense of a car or bike having gears. Instead, a geared electric hub
motor contains a reducing gear mechanism that allows the motor to turns at a
(single fixed gear ratio) faster rate than the wheel or crank that is being
drive. This makes the motor more efficient.
gears may need greasing occasionally, but typically only every 10,000 miles
geared hub motor is likely to be lighter and more compact than a comparable
motors contain a clutch that disconnects the gear when the motor is not
operating, so a geared motor will provide almost zero additional resistance to
turning when the motor is not in use. A bike with a geared motor will therefore
likely feel very like a normal bike to ride when pedaling it without the
- High quality, UK road legal electric bikes will
most often be based on geared motors (whether front hub, rear hub, or crank
drive mounted as below)
direct drive (or non-geared) motor does not contain the reducing gears or
is likely to be heavier, and will add significant resistance when pedaling without
the motor (rather like having the tyres under-inflated)
very powerful motors that generate a lot of heat a direct drive motor is likely
to be more appropriate. However, in general the extra weight of a direct drive
motor makes them less desirable for an electric bike
drive motors do require less maintenance than a geared motor, which may require
occasional greasing of the interlocking reducing gear mechanism.
- Finally, one advantage of direct drive motors is that they allow the possibility of regenerative braking (i.e. operating the motor as a generator) which cannot be done with a geared motor. The bike's momentum is converted by the motor back into electrical energy, simultaneously recharging the battery and providing resistance that slows down the bike (the exact reverse of the process of the motor pushing the bike). This is unlikely to add much to battery range even in fairly hilly terrain, but can be a useful additional braking mechanis
There are also several ways in which a given motor may be mounted on a bike, each of which introduces a specific set of considerations. These are as follows
motor forms the hub of the front bike wheel.
from the motor is directly transferred to rotational force on the front wheel.
- Front wheel systems are relatively easy to
install and give the benefit of "all wheel drive" (i.e. the front
wheel is motorised, the back wheel pedal powered).
must be taken to reinforce the front dropouts (the part of the frame/forks that
holds the axle) with a torque arm or plate that resists rotation of the axle. All
hub motors exert a significant force on the dropouts via the wheel axle when
the motor operates, however front dropouts are usually less robust than rear
ones and failure would be more serious compared to rear dropouts.
- Removal of the wheel (for example for fixing a puncture) is likely to be made more complicated due to wiring and torque arm / plate.
motor forms the hub of the rear bike wheel.
from the motor is directly transferred to rotational force on the rear wheel.
- Rear hub installation is likely to be more
complex than a front one, as the motor wheel must fit with the gears. The
number of gears may be limited and of course it can't be used with internal
hub is more appropriate than front hub for more powerful motors due to lower
risk from dropout failure.
of the wheel (for example for fixing a puncture) is likely to be made more
complicated due to wiring and torque arm / plate
motor is mounted in a housing connected to the bottom bracket and cranks of the
bike. The motor will almost certainly be a geared motor.
- Power from the motor is transferred to the
cranks / bike chain and so to the rear wheel in the same way as a rider
has the key advantage that the motor drives via the bikes gears: this allows
much better efficiency when climbing hills. Installation complexity varies
depending on the bike but has the advantage of not creating any complexity
regarding wheel removal. It will however generally be necessary to remove the
front gear system and replace it with a single chainring, so mid drives work
best with a wide gear range cassette / freewheel / gear hub.
drives vary in complexity of installation, but have the advantage of not
interfering with gearing systems on the rear bike wheel. They can therefore be
used with a wide range of gears as well as internal gear hubs.
drive systems do not make removal of the wheels more complicated, unlike hub