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

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

4. 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?

5. 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°.

6. 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

7. 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

8. 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

9. 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

10. 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.

11. 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.

12. 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.

13. 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 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.

14. 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

15. 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

16. 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

17. 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.

18. 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

19. 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

20. 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

21. 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.

22. 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

23. 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.

24. Mechanisms
PLTW Gateway®
Unit 2 – Lesson 2.2 – Mechanical Systems
Image Resources
Microsoft, Inc. (2008). Clip Art. Retrieved November 25, 2008, from