Page:Motors and motor-driving (1902).djvu/347

Rh In the Phoenix motor bicycle, the Minerva engine is adopted with two or three ingenious additions. The switch is controlled from the handle-bar, the electrical contact being arranged near the engine. The switch lever is so arranged that when further moved the exhaust-valve is lifted. In the same bicycle, the space between the down diagonal and the rear wheel is used for a specially shaped tank for petrol, giving a total available supply sufficient for a run of 200 miles. The Enfield has its motor highly placed in front of the head of the frame and driving the rear wheel, the only combination of this position with rear driving that has been introduced. The Mitchell and the Thomas motor bicycles (which are of American design) have the motor above the bottom tube but close to the head. The Brown machine, which is of English design and construction, follows somewhat the practice of the last two named, but the motor is fixed lower down on the bottom tube. In the Shaw motor bicycle the motor is attached vertically in the rear frame, driving the rear wheel either by belt or chain as desired.

Power transmission, a subject already incidentally mentioned, is an important point with regard to motor bicycles.

Belt-driving was originally the only medium considered, as it overcomes much of the vibration, although the tendency to slip is an obvious disadvantage. The V section belt was selected for the early types, but in the Minerva motor bicycle a twisted belt is used, the slack in which can be taken up by increasing the twists. Even with this, however, there are disadvantages, and when riding in wet weather on sandy roads we have known it to grind the groove of the pulley-wheel, slipping of the belt naturally resulting. Although powdered resin may be a temporary cure for this, the best way is to untwist the belt and twist it in the reverse direction. In the new Werner flat belts with flat pulleys are used, and in the United States an endless raw-hide rope is adopted in some machines.

An innovation is made in the Singer motor bicycle in locating the whole of the mechanism in the driving wheel.