Mechanisms Mechanisms PLTW Gateway Unit 2 – Lesson 2.2 – Mechanical SystemsTW Mechanisms Automation and Robotics FT © 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

Mechanism Movement Rotary Oscillating Linear Reciprocating Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Mechanism Movement Rotary Oscillating Linear Reciprocating

Universal Joint Angular Range > 90˚ and < 270˚ Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Universal Joint Angular Range > 90˚ and < 270˚ Speed and Torque constant Ratio 1:1 Flow of Power reversible 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

Bevel Gear 90˚ Angle Speed and Torque constant Gear Ratio 1:1 Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Bevel Gear 90˚ Angle Speed and Torque constant Gear Ratio 1:1 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. Hand drill Car differential Shaft-driven bicycle

Simple Gear Train with Idler Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Simple Gear Train with Idler Input and Output Shafts parallel Speed is decreased Torque is increased Ratio 4:1 Flow of Power reversible Input and Output Gears same direction Without Idler Gear different direction IDLER GEAR

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. Paper Transport Rollers

Worm and Wheel 90˚ Angle Speed is decreased Torque is increased Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Worm and Wheel 90˚ Angle Speed is decreased Torque is increased Gear Ratio 20:1 Flow of Power NOT reversible Direction of Travel reversible Ratio - The input axle turns 20 times every time the output axle turns once.

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? 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.

Crown and Pinion 90˚ Angle Speed is decreased Torque is increased Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Crown and Pinion 90˚ Angle Speed is decreased Torque is increased Gear Ratio 3.2:1 Flow of Power reversible Direction of Travel reversible A gear ratio of 3.2:1 means that the input gear turns 3.2 times every time the output gear turns 1 time. In other words, for every 32 turns of the input gear, the output gear will turn 10 times. Put the handle on the axle with the larger gear and demonstrate that if your input gear is larger and your output gear is smaller, then the speed will increase and the torque will decrease. Torque and speed are inversely related.

Where Do You Find a Crown and Pinion? Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Where Do You Find a Crown and Pinion? Watches Carousel DVD player How many crown and pinion gears do you see in this pendulum clock? The second pendulum clock built by Christian Huygens, inventor of the pendulum clock, around 1658. This drawing is from his treatise Horologium Oscillatorium, published 1673, Paris, and it records improvements to the mechanism that Huygens had illustrated in the 1658 publication of his invention, titled Horologium. It is a weight-driven clock (the weight chain is removed) with a verge escapement (K,L), with the 1 second pendulum (X) suspended on a cord (V). The large metal plate (T) in front of the pendulum cord is the first illustration of Huygens' 'cycloidal cheeks', an attempt to improve accuracy by forcing the pendulum to follow a cycloidal path, making its swing isochronous. Huygens claimed it achieved an accuracy of 10 seconds per day. Each gear is labeled with the number of teeth it has.

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

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 Pinion Rack

Lead Screw Input Movement rotary Output Movement linear Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Lead Screw Input Movement rotary Output Movement linear 6 Revolutions = 1 in. Flow of Power NOT reversible Force is Increased 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.

Pulley and Belt Input and Output Shaft parallel Speed is increased Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Pulley and Belt Input and Output Shaft parallel Speed is increased Torque is decreased Ratio 1:2.5 Flow of Power is reversible Open Belt wheels turn in same direction Crossed Belt wheels turn in opposite direction

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? Lawn mower Car engine The belt is a continuous band that wraps around the pulleys to transmit power. The ratios are the same as for gears. The only exception is that there are no teeth to count. Instead you use the ratio of the diameter of the pulleys. Another difference is that two pulleys connected by an open belt will rotate in the same direction. If the belt is crossed, the pulleys will rotate in opposite directions. BELTS

Cam and Follower Input Movement rotary Output Movement reciprocating Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Cam and Follower 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 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? Cam shaft As a cam rotates, the flat follower is raised and lowered, converting rotary motion to reciprocating (back and forth) motion.

Crank and Slider Input Movement rotary Output Movement reciprocating Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Crank and Slider Input Movement rotary Output Movement reciprocating Slider Moves 1 in. - diameter of crank Increased Crank increased distance slider moves Flow of Power not reversible

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? 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.

Mechanisms PLTW Gateway® Unit 2 – Lesson 2.2 – Mechanical Systems Image Resources Microsoft, Inc. (2008). Clip Art. Retrieved November 25, 2008, from http://office.microsoft.com/en-us/clipart/default.aspx