Mechanical Devices

• In a class 1 lever, the effort and load are on opposite sides. For example a see-saw.
• In a class 2 lever, the load and effort are on the same side of the fulcrum with the load nearest. For example a wheelbarrow.
• In a class 3 lever, the load and effort are on the same side of the fulcrum, but the effort is nearest. For example, a pair of tweezers.
• Mechanical advantage (lever) = Load / effort
• Velocity ratio (lever) = distance moved by effort / distance moved by load
• Efficiency (lever) = Work done on load / work done by effort x 100
• In a reverse motion linkage the bottom link moves to the left and the top to the right. If the distance between the fixed and moving pivot is equal, output force is the same as the input.
• In a bell crank, the output movement is 90 degrees to the input. The output is greater when the fixed pivot is closer to the output lever.
• The types of cam are pear, eccentric, and snail.
• The types of followers are knife, roller, and flat.
• A pulley and belt system is a system used to transmit rotary motion and torque.
• VR of pulley system = Diameter of driven / diameter of driver
• Speed of driven = rpm of driver / velocity ratio
• Crank and slider mechanisms convert rotary motion to reciprocating motion, for example piston engines in cars are the opposite to this.
• Rpm of driven = rpm of driver / gear ratio
• Compound gear trains are created when one or more of the shafts holds two hears. Used to increase speed and torque in limited space.
• An idler gear is placed between two gears to ensure they have the same direction of motion.
• Bevel gears are used to change the direction of a shaft's rotation, usually through 90 degrees.
• Rack and pinions change rotary motion to linear motion.