Mechanisms Mechanisms PLTW Gateway Unit 2 – Lesson 2.2 – Mechanical Systems Mechanisms Automation and Robotics VEX © 2011 Project Lead The Way, Inc.

Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems What is a Mechanism? A mechanism is the part of a machine which contains two or more pieces arranged so that the motion of one compels the motion of the others. Generally used to: Change the direction of movement Change the type of movement Change the speed of movement Change the amount of torque or force available to do work

Mechanisms - Change Direction Meshed gears in a gear train always turn in opposite directions The flow of power is reversible only if you can make the input shaft turn by turning the output shaft

Mechanisms - Change Movement PLTW Gateway® 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) 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.

Simple Gear Train 1. Input and Output Shafts parallel Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Simple Gear Train 1. Input and Output Shafts parallel 3. A - Speed is constant 4. B – Speed is increased 5. A - Torque is constant 6. B – Torque is decreased 7. A - Ratio 1:1 8. B - Ratio 36 teeth:60 teeth or 3:5 9. Flow of Power reversible 10. Gear direction – opposite A. Driven Drive B. Driven Drive gear is on the input shaft, driven gear is on the output shaft. Drive

Where Do You Find a Simple Gear Train? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Simple Gear Train? 11. Found in: Watch Sewing Machine Motor Watch gears Two meshed gears will rotate in opposite directions.

Simple Gear Train with Idler Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Simple Gear Train with Idler 1. Input and Output Shafts parallel 3. Speed is constant 4. Torque is constant 5. Ratio 1:1 6. Flow of Power reversible 7. Input and Output Gears same direction Without Idler Gear different direction Driven Drive Idler

Where Do You Find a Simple Gear Train with Idler? Mechanisms PLTW Gateway® 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. 8. Found in - Paper Transport Rollers

Bevel Gear 1. 90˚ Angle 2. Speed constant 3. Torque constant Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Bevel Gear 1. 90˚ Angle 2. Speed constant 3. Torque constant 4. Input > Output Speed increases Torque decreases 5. Gear Ratio 1:1 6. Flow of Power reversible

Where Can You Find a Bevel Gear? Mechanisms PLTW Gateway® 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. Using gears with differing numbers of teeth will change the speed and torque. 7. Found in: Hand drill Car differential Shaft-driven bicycle

Differential Gear Gears used – Bevel Axles turn – Same direction Mechanisms PLTW Gateway Unit 2 – Lesson 2.2 – Mechanical Systems Differential Gear Gears used – Bevel Axles turn – Same direction Used in – Vehicles Purpose – Wheels spin at different speeds when turning Howstuffworks.com/differential

Worm and Wheel 1. 90˚ Angle 2. Speed is decreased Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Worm and Wheel Wheel 1. 90˚ Angle 2. Speed is decreased 3. Torque is increased 5. Gear Ratio 24:1 6. Flow of Power NOT reversible 7. Direction of Travel 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 PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Worm and Wheel? 8. Found in: Tuning mechanism on string instruments Electric motors Winch A worm is used to reduce speed and increase torque. The motion is not reversible; a gear cannot drive a worm.

Leadscrew 1. Input Movement rotary 2. Output Movement linear Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Leadscrew 1. Input Movement rotary 2. Output Movement linear 3. Revolutions 4.75 per inch travel 4. Flow of Power Not reversible 5. Force is increased 6. Direction of Travel reversible

Where Do You Find a Lead Screw? Mechanisms PLTW Gateway® 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 move a heavy car. Jack Vice Increases force, not torque, because the output is in a linear direction.

Rack and Pinion 1. Input Movement rotary 2. Output Movement linear Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Rack and Pinion 1. Input Movement rotary 2. Output Movement linear 4. With a Larger Pinion Gear - the rack will move a longer distance 5. Flow of Power reversible 6. Direction of Travel Pinion Rack

Where Do You Find a Rack and Pinion? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Rack and Pinion? Used to convert between rotary and linear motion. Provides gear reduction to make it easier to turn the wheels. 7. Used in steering systems of cars to convert rotary motion of steering wheel to the side to side motion in the wheels. Rack and pinion steering Rack Pinion

Universal Joint Angular Range > 90˚ and < 270˚ Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Universal Joint Angular Range > 90˚ and < 270˚ 2 - 3. Speed and Torque constant 4. Ratio 1:1 5. Flow of Power reversible 6. Input & Output Shafts same direction 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 PLTW Gateway® 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°. www.rqriley.com/imagespln/pattersn_ujoint.jpg

Chain Drive 2. Angle is parallel 3. Speed is increased Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Chain Drive Driven 2. Angle is parallel 3. Speed is increased 4. Torque is decreased 5. Ratio 18:30 or 3:5 6. Smaller drive gear – Speed – decreased Torque - increased 7. Shaft direction same Drive Drive Driven

Where Do You Find a Chain and Sprocket? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Chain and Sprocket? 8. Found in: Bicycle Motorcycle 9. Advantage of Chain and Sprocket over spur gears: Transfer torque and speed over long distances

Belt Drive 2. Shafts parallel 3. Speed constant 4. Torque 5. Ratio 1:1 Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Belt Drive Drive 2. Shafts parallel 3. Speed constant 4. Torque 5. Ratio 1:1 6. Larger drive pulley Speed – increased Torque - decreased 7. Open belt – same direction 8. Crossed belt - opposite Driven

Where Do You Find a Pulley and Belt? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Pulley and Belt? 9. Found in: Lawn mower Car engine BELTS 10. Belts instead of chains: Quieter Less expensive

Crank and Slider 2. Input Movement rotary Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Crank and Slider 2. Input Movement rotary 3. Output Movement reciprocating 4. Slider Moves 2 in. (or diameter of crank) 5. Increased Crank increased distance slider moves 6. Flow of Power not reversible Crank Slider

Where Do You Find a Crank and Slider? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Crank and Slider? 7. 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 2. Input Movement rotary Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Cam and Follower 2. Input Movement rotary 3. Output Movement reciprocating 4. Follower moves up and down 1 time for every revolution of the crank 5. Flow of Power not reversible 6. Direction of Travel not reversible FOLLOWER CAM

Where Do You Find a Cam and Follower? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Cam and Follower? 7. 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.

Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Image Resources Microsoft, Inc. (2008). Clip Art. Retrieved from http://office.microsoft.com/en-us/clipart/default.aspx