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 PLTW Gateway Unit 2 – Lesson 2.2 – Mechanical Systems 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 PLTW Gateway Unit 2 – Lesson 2.2 – Mechanical Systems Mechanisms - Change Speed Gear ratios compare the output (or driven/follower gear) to the input (or drive 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 PLTW Gateway Unit 2 – Lesson 2.2 – Mechanical Systems 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 A. Driven Drive B. Driven Drive Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Simple Gear Train 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? Found in: Watch Sewing Machine Motor Watch gears Two meshed gears will rotate in opposite directions.

Cool Simple Gear Train https://www.youtube.com/watch?v=VoBGau9623I&list=PLE539743FE2BE696B&index=18

Simple Gear Train with Idler Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Simple Gear Train with Idler 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 – Vehicles, to place into reverse. https://www.youtube.com/watch?v=67uDjMz6EpA

Bevel Gear Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Bevel Gear

Where Can You Find a Bevel Gear? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Can You Find a Bevel Gear? Found in: Hand drill/Drill Press- see in action! Car differential Shaft-driven bicycle 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.

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 Wheel Worm Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Worm and Wheel Wheel 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? 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

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 Pinion 1. Input Movement rotary 2. Output Movement linear 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. 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˚ 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 Larger drive gear: Speed is increased Torque is decreased Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Chain Drive Driven Larger drive gear: Speed is increased Torque is decreased Smaller drive gear: Speed is decreased Torque is increased 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? Found in: Bicycle Motorcycle Advantage of Chain and Sprocket over spur gears: Transfer torque and speed over long distances

Belt Drive Drive Driven Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Belt Drive Drive Driven https://www.youtube.com/watch?v=Syp3CW9sFbk&list=PLE539743FE2BE696B&index=29

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? Found in: Lawn mower Car engine BELTS Belts instead of chains: Quieter Less expensive

Crank and Slider Crank Slider Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Crank and Slider 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? 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. https://www.youtube.com/watch?v=RFaLPuKkyAE

Cam and Follower FOLLOWER CAM Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Cam and Follower 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? Found in: Cam shaft As a cam rotates, the flat follower is raised and lowered, converting rotary motion to reciprocating (back and forth) motion. https://www.youtube.com/watch?v=ESRsd1TeOSg

Cool Mechanisms https://www.youtube.com/watch?v=r0y_uNoYqWM&list=PLE539743FE2BE696B&index=15 https://www.youtube.com/watch?v=WR931mtC3l4&list=PLE539743FE2BE696B&index=17 https://www.youtube.com/watch?v=wDdmX6yGCuY&list=PLE539743FE2BE696B&index=28 https://www.youtube.com/watch?v=u9Bh7JqVw-o&index=30&list=PLE539743FE2BE696B

Infinite Mechanisms An infinite mechanism can move in one direction forever- it doesn’t have an end point and this need to reverse direction. These infinite mechanisms are the only mechanisms you’ll be able to use for the pull toy. Bevel Cam and Follower Crank and Slider Simple Gear Train Simple Gear Train with Idler Worm and Wheel

Mechanisms We’re Building Wall Assembly (required for some mechanisms) Mechanisms We’re Building - Wall Assembly Required - Wall Assembly Required - Wall Assembly Required Open Autodesk Inventor. Open the file 00 Wall Asembly from here: T:\Middle School\Melville\Student Technology Files\Vex\Parts\ Wall Assembly - Wall Assembly Required - Wall Assembly Required - Wall Assembly Required T:\Middle School\Melville\Student Technology Files\Vex\Parts