Friction wheel 1 rotates about fixed axis A and contacts two pressure rollers 3 of equal diameter which rotate about axes C and D of sliders 5. Sliders 5 move along fixed guides a. Friction wheel 2 rotates about fixed axis B and is driven by wheel 1 through pressure rollers 3. The required normal force for transmitting a torque is developed by spring 4 which connects sliders 5 .
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