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Thursday, May 14, 2009

E+ Electric Bike - the world's most advanced electric bicycle?

With the increasing popularity of the electrically assisted pushbike we are starting to see some innovative designs hit the market. While hub motors are the number one solution for mounting the electric motor within a bike frame, either in the front or rear wheel, mounting the battery pack and motor drive electronics has remained a challenge when taking into consideration practically and aesthetics. The folks at Electric Motion Systems think they have the answer with a combination of a 750 watt rear wheel mounted hub motor with built-in motor drive electronics paired with a battery pack mounted in the front wheel hub.

The E+ Electric Bike is available in six styles of bike that are all a variation on a hard-tail mountain bike. The E+ comes standard with a 750 watt BLDC rear hub motor but there is a high torque 85 Nm 1kw hub motor as an upgrade option. Both hub motors have built in inverters so there’s one less box to find mounting space on the bike frame for. The front hub mounted battery pack is something we’ve never seen before on an e-bike. The internal layout is very similar to a hub motor with the stationary inner structure (called the stator) attached to the axle while the outer housing is attached to the rim via spokes and rotates as part of the wheel. Thirty NiMH battery cells are arranged in six groups of five cells arranged in a polygon layout parallel to the axle and mounted on the stator. The battery pack puts out 36 volts at 9 amp hour giving a battery capacity of 324 watt hour. (0.324kw/hr). No electric only range is quoted as this is very dependent on terrain, how much you pedal and the amount of regeneration possible but each battery charge should give between 20 and 40 miles (32 – 64 km). A full charge from a 110v wall socket will take four to six hours and cost about $0.03.

The E+ has a handlbar mounted LCD display where the rider can select 19 different cycling modes that range from full electric to pedal only modes. One of the E+ modes offers to let you set the cycling mode for increased resistance to give you a greater workout even if there are no hills in sight. While this could well be a useful feature, it also highlights one of the side effects of BLDC hub motors - they do not freewheel. Because a BLDC hub motor contains permanent magnets even when no power is applied there is still magnetic attraction between the magnets and the poles on the stator meaning there is always cogging resistance. The company says this should only be a problem with a flat battery on extended flat surface riding, as with any kind of undulation the motor will regenerate on the down hills just enough to provide power assistance up the next hill.

The LCD-display also shows speed, distance traveled, battery capacity, cruise control option, and 19 cycling modes. It also displays trip-specific data such as distance of trip, duration, and average speeds. Pocket-sized and removable for safe and easy storage, when the display is removed, the battery is disabled and the motor is put into full resistance mode, making pedaling virtually impossible. This unit has backlighting (0-100%) and automatically adjusts the contrast of display depending on outdoor conditions

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