Wheels and Pulleys Introduction to Engineering and Technology Concepts Mindjog 1. How much effort will be needed to lift a 100 pound load if distance to effort is five feet and distance to resistance is one foot? 2. How much effort will be needed to lift a 48 pound load if distance to effort is two feet and distance to resistance is 8 feet? Wheel & Axle Wheel and Axle The Wheel and Axle work off the same principle as the lever. Wheel diameter = 8 Axle diameter = 1 Produce an 8/1 MA Wheel and Axle If the effort (input) is applied to the wheel, the axle is the resistance (output). – This will produce a mechanical advantage equal to the size ratio of the wheel as compared to the axle. Wheel diameter = 8 R E Axle diameter = 1 Produces an MA of 8 What class lever is this wheel configuration? Wheel and Axle If the effort (input) is applied to the axle, the wheel is the resistance (output). – This will create an increase in output distance but it will take more effort to turn. Wheel diameter = 8 E R Axle diameter = 1 Produces an MA of 1/8 What class lever is this wheel configuration? IDENTIFY ITEMS THAT APPLY THE PRINCIPLE OF THE WHEEL AND AXLE IN THEIR OPERATION. GIVE AT LEAST TWO EXAMPLES FOR EACH CLASS. Wheel Examples (2nd Class) Doorknob Car Jack Screwdriver Telescope/ Car Climate Microscope Knobs Controls Windmill/Wind Dimmer Switch Turbines Pencil Sharpener Waterwheel Lamp Switch Wheel of Fortune Hamster Wheel The Price is Right Pottery Wheel Wheel Examples (3rd Class) Ferris Wheel Carousel/Merry-Go- Wheelbarrow Round Clock Hands Pizza Cutter Band Saw Paint Roller Circular Saw Fan Blade Blender/Grinder Boat or Airplane Bike/Car Tires Propeller Fishing Reel Helicopter Rotor Big Wheel™ Mechanical Transmission A device which accomplishes one, or more, of the following: – Transfer motion from one point to another – Increase output speed OR force – Change direction of motion – Change type of motion Motion Four types of motion: – LINEAR – Straight line, one direction – RECIPROCATING – straight line, back and forth – ROTATIONAL – Circular – OSCILLATING - Swinging Pulleys A pulley is basically a wheel with a groove in the circumference of the wheel, with a belt or cable being fed around the groove. Pulleys create a mechanical advantage by connecting a small input drive pulley to a larger follower with a belt. Driver Follower (Effort) (Resistance) Mechanical Advantage MA = FOLLOWER ÷ DRIVER Driver Follower 1mm 4mm The Pulley Drive Train above produces an MA of 4. This means 10 lbs of input torque will create 40 lbs output, but the driver must rotate 4 times to rotate output 1 time. Speed is reduced by 4. Mechanical Advantage MA = FOLLOWER ÷ DRIVER Driver Follower 3mm 9mm Driver Follower 2mm 14mm Increasing Speed Increase the speed of the output by using a larger driver gear and a smaller follower gear. Speed increases and power decreases. Driver Follower 4mm 1mm Compound Drive Pulley Trains • A Compound Drive Pulley Train has pairs of pulleys working in combination, with the follower of one pulley sharing the same axle as the driver of the next sequential pulley train. Compound Drive Pulley Trains MA = (FOLLOWER 1 X FOLLOWER 2) ÷ (DRIVER 1 x DRIVER 2) – Driver 1 = 2mm Follower 1 = 8mm – Driver 2 = 3mm Follower 2 = 9mm Compound Drive Pulley Trains MA = (FOLLOWER 1 X FOLLOWER 2) ÷ (DRIVER 1 x DRIVER 2) – Driver 1 = 3mm Follower 1 = 9mm – Driver 2 = 2mm Follower 2 = 14mm Problem Sketch the following two pulley trains: – A: Simple pulley train with belt wrapped so both pulleys rotate in same direction. – B. Simple pulley train with belt wrapped so both pulleys rotate in opposite direction. Solution A: Simple pulley train with belt wrapped so both pulleys rotate in same direction. Solution B. Simple pulley train with belt wrapped so both pulleys rotate in opposite direction. Problem Calculate the mechanical advantage of the compound pulley drive train model. – Show your work. – Small Pulley Diameter = 25mm – Large Pulley Diameter = 100mm Pulleys Lifting Pulleys Lifting Pulleys in transmission systems – Single pulley – Moveable pulley – Block and Tackle Single Pulley Provides change of motion, but no mechanical advantage 100 ft 100 lbs 100 lbs 100 lbs 100 lbs Single Pulley The resistance arm and the effort arm are both the radius of the pulley. Since they are equal, there is no mechanical advantage. Moveable pulley Provides change of direction and a mechanical advantage of 1:2 (at the expense of having to increase the amount of line to pull) 50 lbs 50 lbs 50 lbs 50 lbs 100 lbs 100 lbs Moveable pulley A moveable pulley is a second-class pulley. The effort arm is the diameter and the resistance arm is the radius. MA = dE ÷ dR MA = 2 ÷ 1 = 2 Block and Tackle Multiple pulleys providing a greater mechanical advantage. MA is determined by the number of pulleys. 25 lbs 25 lbs 25 lbs 25 lbs 25 lbs 100 lbs 100 lbs Block and Tackle Gun Tackle Luff Tackle Block and Tackle Block and Tackle Review Give real-world example of each of the following pulleys. – Force Multiplier – Speed Multiplier – Direction Changer Give one example of a simple machine or transmission that changes output motion. Identify both input and output motions.
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