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A 250W electric motor (UK street-legal for a tricycle) fitted with a friction roller studded with 50 self-tapping screws is used to provide a good grip on the tyre, wet or dry. Power to the motor is controlled by a PWM controller attached by a gear cable to a handlebar lever to provide finely-controllable pedal-assist. The motor is mounted on a sprung, damped platform which in its rest position holds the friction roller away from the tyre, allowing the Trice XL to be pedalled normally. The platform is pulled downwards by a gear cable attached to a handlebar lever to bring the friction roller into firm contact with the tyre. A handlebar switch ensures that power to the motor is interrupted when the rider reaches for the brake. Friction roller diameter is a critical factor with a motor of only 250W, a smaller roller giving better hill climbing and a larger roller giving higher speed. The motor used has a maximum speed of 2750RPM, which means a 1.894 inch diameter roller will give a top speed along the ground of 15.5 MPH, which is the legal limit.
