11/8/2023 0 Comments Chain drive pdf basics![]() ![]() ![]() There are a few different types of pulleys that I'll explain, which apply to multiple types of pulley systems. The upper wheel thus exerts twice the torque, but half the speed. The speed ratio also tells us something about the torque of the system, as the ratio of the output torque over the input torque is equal to the speed ratio. It takes 2 rotations of the lower wheel to rotate the upper wheel once. In the image above, the lower, driving pulley has a reference diameter of 20 mm and the upper pulley has a radius of 40 mm, making the ratio 2:1. With multiple pulleys, the ratio for each segment of the mechanism has to be calculated to determine the overall ratio. Calculating the speed ratio of a more complicated pulley system is fairly simple as long as you take it step by step. The speed ratio is equivalent to the reference diameter of the output pulley over the reference diameter of the input pulley in a two pulley system. This is what you will use to calculate the speed ratio ![]() Reference/Pitch Diameter: The working diameter of the pulley, where the belt or cable contacts the pulley. If you've calculated gear ratios, it is almost exactly the same! This is all based on a pulley's reference diameter, as defined below: The Speed Ratio is the ratio of angular velocity of the input pulley of a system to the angular velocity of the output pulley. Because most pulleys are driven by the friction between the pulley and the belt, if a part of a mechanism jams, then the belt transmitting power will slip on its pulleys instead of stalling the motor. Belts and pulleys can be used to transmit power over larger distances and in constricted spaces, which is one advantage they have over gears. Pulleys are also one of a few different methods of transmitting rotation from one axis to another. Certain types of pulley systems, like the block and tackle (to be explained later), can actually lessen the applied force needed to lift an object via a system of moving pulleys and lines, which can be very useful in high-load situations. Because the rope or belt is looped around the circumference of the pulley, the force of the object on one end of the rope can loop around the pulley to the other end. Elevators, cranes, and boats all use pulleys because a pulley changes the direction of the applied force on the belt. Pulleys are probably most commonly used for lifting heavy loads and transmitting power across axes. ![]()
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