Mechanisms Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Mechanisms

What is a Mechanism? In a machine - one part causing another to move Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems What is a Mechanism? In a machine - one part causing another to move Used to transfer or change speed, torque, force, type of motion and / or direction of motion.

Mechanisms - Change Direction Meshed gears in a gear train always turn in opposite directions

Mechanisms - Change Movement Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Mechanisms - Change Movement Rotary Oscillating Linear Reciprocating

Mechanisms - Change Speed Gear ratios compare the output (or driven gear) to the input (or drive gear) Output : Input Gear Ratios can be determined using number (n) of teeth on the gear or diameter (d) of the gear If the output gear is larger than the input gear the speed will decrease If the output gear is smaller than the input gear the speed will increase

Mechanisms – Change Force or Torque A force is a push or pull in a straight line. Torque is a push or pull in a circular direction or twisting motion

Simple Gear Train A. B. Input and Output Shafts parallel (A & B) Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Simple Gear Train Input and Output Shafts parallel (A & B) A – Ratio 1:1 [Output to Input] Speed is constant Torque is constant B – Ratio 3:5 [Output to Input] 36 teeth : 60 teeth Speed is increased Torque is decreased Flow of power - reversible Motion - rotational to rotational Direction – opposite Driven / Output A. Drive / Input Driven / output Drive gear is on the input shaft, driven gear is on the output shaft. B. Drive / Input

Where Do You Find a Simple Gear Train? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Simple Gear Train? Found in: Watch Sewing Machine Motor Watch gears Two meshed gears will rotate in opposite directions

Simple Gear Train with Idler Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Simple Gear Train with Idler Input and Output Shafts parallel Ratio 1:1 [Output to Input] Speed is constant Torque is constant Flow of power - reversible Motion - rotational to rotational to rotational Direction – same Driven / Output Drive / Input Idler

Where Do You Find a Simple Gear Train with Idler? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Simple Gear Train with Idler? Two meshed gears will rotate in opposite directions. An Idler Gear allows the drive and driven gears to rotate in the same direction. 7. Found in - Paper Transport Rollers / Car Transmission

Bevel Gear Input and Output Shafts 90 degrees Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Bevel Gear Input and Output Shafts 90 degrees Ratio 1:1 [Output to Input] Speed is constant Torque is constant Flow of power - reversible Motion - rotational to rotational Direction – same

Where Can You Find a Bevel Gear? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Can You Find a Bevel Gear? The bevel gear is used to change rotational motion at a 90˚ angle. Found in: Hand drill Car Differential

Differential Gear Gears used – Bevel Mechanisms Gateway To Technology Unit 2 – Lesson 2.2 – Mechanical Systems Differential Gear Gears used – Bevel Used in – rear end of rear wheel drive vehicles Purpose – Wheels spin at different speeds when turning http://auto.howstuffworks.com/differential.htm

Worm and Wheel Input and Output Shafts 90 Degrees Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Worm and Wheel Wheel Input and Output Shafts 90 Degrees Ratio 1:24 [Output to Input] Speed is decreased Torque is increased Flow of power – not reversible Motion - rotational to rotational Direction – same & reversible Ratio - The input axle turns 32 times every time the output axle turns once. Worm

Where Do You Find a Worm and Wheel? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Worm and Wheel? Found in: Tuning mechanism on string instruments Electric motors Winch A worm is used to reduce speed and increase torque.

Leadscrew Speed is decreased Force is increased Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Leadscrew Speed is decreased Force is increased Revolutions 4.75 (per design) Flow of power – not reversible Motion - rotational to linear Direction – reversible

Where Do You Find a Lead Screw? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Lead Screw? Changes rotary movement into linear movement Significantly increases force A person can put a little force into turning the handle to lift a heavy car Jack Vice Increases force, not torque, because the output is in a linear direction.

Rack and Pinion Force increased Input Movement rotary Output Movement Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Rack and Pinion Force increased Input Movement rotary Output Movement linear With a Larger Pinion Gear - the rack will move a longer distance Flow of power - reversible Motion - rotational to linear Direction – same & Reversible Pinion Rack

Where Do You Find a Rack and Pinion? Mechanisms Where Do You Find a Rack and Pinion? Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Used in steering systems of cars to convert rotary motion of steering wheel to the side to side motion in the wheels. Used to convert between rotary and linear motion. Provides gear reduction to make it easier to turn the wheels. Rack Pinion

Universal Joint Angular Range > 90˚ and < 270˚ Ratio 1:1 Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Universal Joint Angular Range > 90˚ and < 270˚ Ratio 1:1 Speed is constant Torque is constant Flow of power - reversible Motion - rotational to rotational Direction – same Angular Range – Discuss the purpose of a universal joint as being flexible, for example, when your vehicle hits a pot hole the drive shaft doesn’t break. Flow of Power – If you turn the output shaft, will the input shaft turn? Direction of Travel – Can the handle be turned both clockwise and counterclockwise?

Where Can You Find a Universal Joint? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Can You Find a Universal Joint? Drive shaft of vehicles Power take-off Universal joints are used to transmit rotary movement at an angle that is not 90°.

Chain Drive A - Shafts are parallel Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Chain Drive A - Shafts are parallel Ratio 30:18 or 5:3 [Output to Input] Speed is increased Torque is decreased B – Shafts are parallel Ratio 18:30 or 3:5 [Output to Input] Speed is decreased Torque is increased Flow of power - reversible Motion - rotational to rotational Direction – same Driven / Output A Drive / Input Drive / Input Driven / Output B

Where Do You Find a Chain and Sprocket? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Chain and Sprocket? Found in: Bicycle Motorcycle Advantage of Chain and Sprocket over spur gears: Transfer torque and speed over long distances

Belt Drive Input and Output Shafts parallel Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Belt Drive Drive Input and Output Shafts parallel Ratio 1:1 [Output to Input] Speed is constant Torque is constant Flow of power - reversible Motion - rotational to rotational to rotational Direction – open belt same - crossed belt opposite Driven

Where Do You Find a Pulley and Belt? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Pulley and Belt? Found in: Lawn mower Car engine BELTS Belts instead of chains: Quieter /Less expensive Less durable / slip

Crank and Slider Speed / Force – N/A Input Movement rotary Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Crank and Slider Speed / Force – N/A Input Movement rotary Output Movement reciprocating Slider moves- diameter of the crank Flow of power – not reversible Direction – same & reversible Crank Slider

Where Do You Find a Crank and Slider? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Crank and Slider? Found in: Steam train Internal combustion engine As the slider moves to the right, the connecting rod pushes the wheel round for the first 180 degrees of wheel rotation. When the slider begins to move back into the tube, the connecting rod pulls the wheel round to complete the rotation.

Cam and Follower Speed & Force N/A Input Movement rotary Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Cam and Follower Speed & Force N/A Input Movement rotary Output Movement reciprocating Follower moves up and down 1 time for every revolution of the crank Flow of Power not reversible Direction of Travel not reversible FOLLOWER CAM

Where Do You Find a Cam and Follower? Mechanisms Gateway To Technology® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Cam and Follower? Found in: Cam shaft As a cam rotates, the flat follower is raised and lowered, converting rotary motion to reciprocating (back and forth) motion. The cam pictured here would be reversible, as it is symmetrical.