The Electric Mountain Bike.
4QD 120 Amp PWM Controller Ignition Switch and Throttle Potentiometer Bosch 24V 1HP motor EMD Gearbox and custom motor adapter Emergency Cut-Off Switch Panniers containing 2 YUASA 12V 24AH Sealed Lead Acid Batteries Shimano Free-Wheeling Crank

Above is the third prototype of the Electric Mountain Bike. Point to the various components in the picture above to identify them.

Frame - the frame is a cheap second hand one with no frills other than twist-grip gear change.

Motor - the motor is a Bosch 24V 750W unit. The part number is 0 130 302 014. I burned out a 300W EMD motor going up a long incline. This one has built in fan cooling so hopefully it will last longer. These motors are available individually from Ellis Components.

Gearbox - the gearbox is an EMD unit. These are available from Rebel Replicas. Mine came off another electrically assisted bike (along with the EMD motor mentioned above) but it had a plastic gear which stripped while going up a steep incline. I was able to get a phosphor-bronze replacement from Rebel Replicas. The motor is attached to the gearbox with a custom adapter plate which was machined up for me by a local precision engineer. The motor shaft and gearbox input shaft are connected using a flexible coupling to reduce vibration. A free-wheeling sprocket is used on the gearbox output shaft and this is connected by a short chain to the bike's crank sprocket.

Crank - the Shimano free-wheeling crank came off the same bike as the EMD motor and gearbox. Apparently these are no longer available. The remaining sprocket on the crank is used to drive the rear Derailiuer gears in the normal way. Thus I have five gears to choose from.

Motor Controller - the Controller is a 4QD 120 Amp unit. The order code is SCO-120-24. It is a lovely piece of kit - highly recommended. Visit the 4QD website at The ignition switch and throttle pot. are mounted in a small box behind the handlebars. The throttle is controlled by the redundant twist grip gear changer. I also mounted an emergency cut-off switch behind the gearbox and in series with the motor.

Batteries - these are two YUASA 12V, 24 Amp Hour sealed lead acid units wired in series to provide 24V. These are the deep-discharge versions specifically designed to be run almost flat before they are recharged.

See below for a second picture of the bike:

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