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

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. 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

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

5. 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.

6. 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.

7. 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

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?
Found in:
Watch
Sewing Machine
Motor
Watch gears
Two meshed gears will rotate in opposite directions.

9. Cool Simple Gear Train

10. Simple Gear Train with Idler
Mechanisms
PLTW Gateway®
Unit 2 – Lesson 2.2 – Mechanical Systems
Simple Gear Train with Idler
Driven
Drive
Idler

11. 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.

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

13. 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.

14. 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

15. 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

16. 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.

17. 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

18. 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.

19. 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

20. 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

21. 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?

22. 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°.

23. 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

24. 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

25. Belt Drive Drive Driven
Mechanisms
PLTW Gateway®
Unit 2 – Lesson 2.2 – Mechanical Systems
Belt Drive
Drive
Driven

26. 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

27. Crank and Slider Crank Slider Mechanisms PLTW Gateway®
Unit 2 – Lesson 2.2 – Mechanical Systems
Crank and Slider
Crank
Slider

28. 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.

29. Cam and Follower FOLLOWER CAM Mechanisms PLTW Gateway®
Unit 2 – Lesson 2.2 – Mechanical Systems
Cam and Follower
FOLLOWER
CAM

30. 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.

31. Cool Mechanisms

32. Infinite Mechanisms
An infinite mechanism can move in one direction forever- it doesn’t have an end point and thus 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

33. VEX Robotics Tip #1 Simple Gears can be used so that
the rod used for the input (wheels)
does not need to be the same rod
used for the output.

34. VEX Robotics Tip #2 These can be bent
(if necessary, ask Mr. Melville first).
These rods can be cut to length (if necessary, ask Mr. Melville first).

35. VEX Robotics Tip #3 Rods work best when they go
through at least 2 walls and when
they’re anchored by as many
black plastic anchors as possible (4 in this example).

36. VEX Robotics Tip #4
Cam pivot example- add pic

37. Mechanisms We’re Building
Wall Assembly (required for some mechanisms)
Mechanisms We’re Building
- Wall Assembly Required
- Wall Assembly Required
- MODIFIED 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