1. MECHANISMS Mechanisms Mechanisms Automation and Robotics VEX
© 2011 Project Lead The Way, Inc.

2. Mechanisms
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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. Mechanisms - Change Direction
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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

4. Mechanisms - Change Movement
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Unit 2 – Lesson 2.2 – Mechanical Systems
Mechanisms - Change Movement
Rotary
Oscillating
Linear
Reciprocating

5. Mechanisms - Change Speed
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Unit 2 – Lesson 2.2 – Mechanical Systems
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.

6. Mechanisms – Change Force or Torque
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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.

7. Simple Gear Train 1. Input and Output Shafts parallel
Mechanisms
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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

8. 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.

9. Simple Gear Train with Idler
Mechanisms
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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

10. Where Do You Find a Simple Gear Train with Idler?
Mechanisms
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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

11. Bevel Gear 1. 90˚ Angle 2. Speed constant 3. Torque constant
Mechanisms
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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

12. Where Can You Find a Bevel Gear?
Mechanisms
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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

13. 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

14. Worm and Wheel 1. 90˚ Angle 2. Speed is decreased
Mechanisms
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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

15. Where Do You Find a Worm and Wheel?
Mechanisms
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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.

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

17. Where Do You Find a Lead Screw?
Mechanisms
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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. Rack and Pinion 1. Input Movement rotary 2. Output Movement linear
Mechanisms
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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

19. Where Do You Find a Rack and Pinion?
Mechanisms
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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

20. Universal Joint Angular Range > 90˚ and < 270˚
Mechanisms
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Unit 2 – Lesson 2.2 – Mechanical Systems
Universal Joint
Angular Range
> 90˚ and < 270˚
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?

21. 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°.

22. Chain Drive 2. Angle is parallel 3. Speed is increased
Mechanisms
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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

23. Where Do You Find a Chain and Sprocket?
Mechanisms
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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

24. Belt Drive 2. Shafts parallel 3. Speed constant 4. Torque 5. Ratio 1:1
Mechanisms
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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

25. Where Do You Find a Pulley and Belt?
Mechanisms
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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

26. Crank and Slider 2. Input Movement rotary
Mechanisms
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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

27. 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.

28. Cam and Follower 2. Input Movement rotary
Mechanisms
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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

29. Where Do You Find a Cam and Follower?
Mechanisms
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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.

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