FIGURE 3. The Sunbeam three speed hub of the 1950s. You can see there are two ri

Question

FIGURE 3. The Sunbeam three speed hub of the 1950s. You can see there are two ring gears (one of which is fixed to the sprocket and another that is free to rotate) four planet gears, and two sun gears one of which is fixed to the axle. Image from Google images. Figure 3 shows parts belonging to the Sunbeam transmission. note there are two ring gears and two sun gears. One of the sun gears for instance can be fixed to the sprocket. One of the ring gears can be fixed to turn the wheel. This leaves the planet carrier to be fixed perhaps to the bicycle frame-locked in place, other words-while the planet gears themselves are still free to rotate. Show why such an arrangement, which is always used in an automotive transmission, is absolutely useless for a bicycle.

Explanation / Answer

This arrangement requires extremely large torques to initiate movement. On a bicycle, powered by a human, applying this much torque would require a large number of speed gears and an inefficient system with respect to size and complexity.

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