EBike Motors Hub

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An ebike hubmotor is a motor within the front or rear wheel of the bicycle.[1] They come in two basic types: direct drive and geared.

Stength of the bike's dropouts and potential clashes between the motor and disk brakes are key factors to consider when using a hub motor.[2]

Contents

Direct Drive Hubmotors

Direct drive hubmotors are the simplest type of motor, since they do not have gears or a clutch. The electric motor is built right into the hub, with the windings attached to the axle, and the magnets arranged around the winding on the outer rim of the hub. Compared with geared motors, they are simpler and have fewer moving parts. They are also called outrunner motors, since the moving part is on the outside. This page describes potential failure modes for direct drive motors.

Benefits:

Drawbacks:

Common Direct Drive Hubmotors

Golden Motor
Crystalyte
Nine Continent
Aotema

Aotema hub motors used to be marketed primarily by Wilderness Energy (now out of business) and sold as the BL-36. It is a brushless motor with no sensors. Drawing ~750w on 36v expect a top speed of around 23 mph with 700c tires.

Geared Hubmotors

Geared hubmotors have a more complicated design. The motor inside turns a set of planetary gears (typically using a 5:1 reduction ratio). The motor spins faster than for direct drive motors, due to this gear ratio. Most planetary gearmotors also have a freewheeling clutch built into them.

Benefits:

Drawbacks:

Find a comprehensive list with characteristics of brushless geared hubmotors on the ES forum by voicecoils 2008.

This graph was created by the ebikes.ca drive simulator, to compare the efficiency, torque and power of a common direct vs a geared drives with equal top speed.

Geared vs direct.jpg

Common geared Hubmotors

Bafang

There are various 180-250W outrunner motors for both front and rear wheel (SWXB, SWXH, SWXK, SWXU....), max. diameter: ~120mm or 143.5mm, gear reduction ~4:1 or 4.43:1 (depending on version), different winds are available for 24-36V and 20"-28" wheels.

500Watts, 36-48V, front (QBPM)or rear (BPM), max. diameter :~180mm, gear reduction ~5:1, available Winds (pdf file) [24] and thread [25] Specs page: BPM Teardown and Specs Thread [26]

similar to BPM, but with a freewheel compatible to shimano hyperglide cassettes, instead the common BSA threads

Similar to SWXH but with a freewheel compatible to shimano hyperglide cassettes, instead the common BSA threads

Bafang official homepage: [27]

Article with lots of pics from BPM and MAC [28]

Puma/MAC/BMC

These three motors are very similar. Their very high pole count and a 5:1 gear reduction give them increased torque. They are available in different winds for 20-28" wheels and 24-48V battery voltage. The BMC has thinner laminations and freewheel threads made of steel (rather than alloy).

This thread discusses the differences[29]. It is common to swap the nylon planet gears for stronger composite gears or steel gears, these are available at various e-bike shops on the net.

Goldenmotor_MBG

similar to Bafang SWXH

TongXin_/_Weifeng

Main Article: TongXin_/_Weifeng

Friction drive inrunner hubmotor. Very lightweight (<2kg) and small, upto 180Watts continous output. Almost silent and a very high reduction, but slightly reduced efficiency. There are two versions, the original and the newer and even more light weight Keyde.

Cute

All cute motors are inrunner motors with a power rating of about 250W. The Q128 is said to be the weakest one, even if rated at 500W. The Q75 that came to market in 2013, is the smallest (92mm/110mm spokes flange diameter) and most lightweight (1.2kg) Hubmotor.


Other brands

helical geared inrunner hub motor with steel gears [30]

2-Speed Motors

These have a much better climbing ability than common single speed motors of the same size. The second gear is introduced by spinning the motor backwards and engage a different gear by an additional freewheel. There is no need for mechanical actuation. This is called retro-direct 2-speed drive and is well known since decades. However, the drive can normally not be spun backwards since the two gears would fight each other. But this issue was solved with the 2-speed motors. [31]

Lifespan and Maintenance

Motors with brushes need the brushes replaced from time to time.[32]

However, most motors are brushless. The only wear items on brushless motors are the bearings, so these motors can last 10,000km or more.[33] Hub motors are usually sealed and do not require any maintenance.[34]

Front vs Rear wheel

This thread discusses the pro's and cons of front vs rear hub motors: http://endless-sphere.com/forums/viewtopic.php?f=3&t=26625

Installation on the front wheel is often simpler, however the rear wheel is safer- especially for more powerful motors.[35]

External links

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