A gear mechanism is used between the crank and the belt pulley.
When stepping on the belt pulley, the crank drives the gear to propel drive the belt pulley at the same time with a ratio of 1:2.6. Therefore, the enlarged differential disc set on the crank is equivalent to 2.6 times the number of teeth of the belt pulley. Reduce the tooth number and the belt angle between the front and rear discs. Combining the above advantages can effectively increase the lifespan of the belt.