Basic principle of operation

Variable pulleys are mechanical variators, serving continuously variable rotational speed changes. By changing the position of the belt on the conical control pulley, the position on the spring pulley is also automatically adjusted (changed), which enables different rotational speeds on the output shaft. Changing the diameter on the control pulley can be done manually or by electromechanical transmission - see possible solutions shown:

manual modes of speed control
electromechanical mode of speed control
hydraulic mode of speed control