1. Gears & VEX

2. Agenda Essential Terminology Gear Types Gearing Up/Gearing Down
gear testing apparatus
Essential Terminology
Gear Types
Gearing Up/Gearing Down
Direction
Gear Ratios
Example
Application: Sumo-Bot Competition

3. Essential Terminology
Driver – gear attached to a motor
Follower – gear doing useful work
Idler – gear between the driver and follower
Gear Train – a row of gears
Geared Up – the follower moves faster than the driver
Geared Down – the follower moves slower than the driver
Compound gears – a gear train with multiple gears on one axle

4. Do you get it? B A Which gear is the driver (A or B)?
motor
Which gear is the driver (A or B)?
Which gear is the follower (A or B)?

5. Do you get it? B A Which gear is the driver (A or B)? → A
motor
Which gear is the driver (A or B)? → A
Which gear is the follower (A or B)? → B

6. Do you get it? A B C Which gear is the follower (A, B, or C)?
wheel
motor A B C
Which gear is the follower (A, B, or C)?
Which gear is the driver (A, B, or C)?
Which gear is the idler (A, B, or C)?

7. Do you get it? A B C Which gear is the follower (A, B, or C)? → C
wheel
motor A B C
Which gear is the follower (A, B, or C)? → C
Which gear is the driver (A, B, or C)? → A
Which gear is the idler (A, B, or C)? → B

8. Gear Types
spur gears
differential
bevel gears
rack & pinion
worm gear

9. Spur Gears
12 tooth
24 tooth
84 tooth
36 tooth
60 tooth

10. Worm gears allow axles at right angles to transfer rotational motion.

11. Bevel gears allow rotational motion to be transferred at right angles.

12. Rack & Pinion pinion rack
Racks and pinions are used to translate rotational motion into linear motion.

13. Differential
Differentials are devices that allow each of the axles to rotate at different speeds, while supplying equal torque to each of them.

14. Sprockets & Chains
Sprockets inside the same chain rotate in the same direction.
Sprockets outside the chain rotate in the opposite direction.

15. Pulleys & Belts Pulleys and belts are not available for VEX
Sometimes tank treads can be used as belts.

16. Direction even number of gears: driver & follower turn in
opposite directions
odd number of gears:
same direction
driver
driver
follower
follower
driver

17. Would the follower gear move clockwise or counterclockwise?
Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?

18. Would the follower gear move clockwise or counterclockwise?
Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?

19. Would the follower gear move clockwise or counterclockwise?
Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?

20. Would the follower gear move clockwise or counterclockwise?
Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?

21. Geared Up large driver turns small follower increases speed
decreases torque (turning force)
follower
driver
driven gear
follower gear

22. Geared Down small driver turns large follower
increases torque (turning force)
decreases speed
driver
follower
driven gear
follower gear

23. Use the following rules to calculate gear ratios.
Gear Analysis
To analyze any gear train you need to:
Locate the driver gear
Locate the follower gear
Calculate the Gear Ratio
Use the following rules to calculate gear ratios.

24. Gear Ratios (determining what a gear will do)
Example Gear Ratio:
⅓ or 1:3
read as 1 to 3
1 turn of the driver will turn the follower 3 times

25. What is the gear ratio?
84 tooth driver
60 tooth follower

26. What is the gear ratio?
driver
follower

27. Long Gear Trains Ignore the idler gears! Gear Ratio = 24/40 = 3/5
The gear attached to the motor is the driver.
The gear doing work is the follower.
All in-between gears are idlers.
Ignore the idler gears!
Follower
Gear Ratio = 24/40
= 3/5
3 turns of the 40 tooth gear will turn the 24 tooth gear 5 times.
Idlers
Driver

28. Compound Gears (Multiple Gears on One Axle)
Pair up drivers and followers
Start a new driver/follower pair if an axle has a second gear attached.
Multiply the gear ratios of all the driver/follower pairs. D2
Gear 1 = 12 teeth Gear 2 = 36 teeth
Gear 3 = 12 teeth Gear 4 = 60 teeth

29. Compound Gears (Multiple Gears on One Axle)
Pair up drivers and followers
Start a new driver/follower pair if an axle has a second gear attached.
Multiply the gear ratios of all the driver/follower pairs.
Gear 1 & Gear 2: D2
Gear 1 = 12 teeth Gear 2 = 36 teeth
Gear 3 = 12 teeth Gear 4 = 60 teeth

30. Compound Gears (Multiple Gears on One Axle)
Pair up drivers and followers
Start a new driver/follower pair if an axle has a second gear attached.
Multiply the gear ratios of all the driver/follower pairs.
Gear 1 & Gear 2: D2
Gear 3 & Gear 4:
Multiply the gear ratios:
Gear 1 = 12 teeth Gear 2 = 36 teeth
Gear 3 = 12 teeth Gear 4 = 60 teeth

31. Compound Gears (Multiple Gears on One Axle)
Pair up drivers and followers
Start a new driver/follower pair if an axle has a second gear attached.
Multiply the gear ratios of all the driver/follower pairs.
Gear 1 & Gear 2: D2
Gear 3 & Gear 4:
Multiply the gear ratios:
Gear 1 = 12 teeth Gear 2 = 36 teeth
Gear 3 = 12 teeth Gear 4 = 60 teeth
15:1

32. Calculate the Gear Ratio (Assume the last axle does the useful work)4
12t
36t 3 2 1

33. Calculate the Gear Ratio (Assume the last axle does the useful work)
Pair 1:
36t
12t
12t 4
12t
36t 3 2 1

34. Calculate the Gear Ratio (Assume the last axle does the useful work)
Pair 1:
36t
12t
12t 4
Pair 2:
12t
36t 3 2 1

35. Calculate the Gear Ratio (Assume the last axle does the useful work)
Pair 1:
36t
12t
12t 4
Pair 2:
12t
36t 3 2 1
Pair 3:

36. Calculate the Gear Ratio (Assume the last axle does the useful work)
Pair 1:
36t
12t
12t 4
Pair 2:
12t
36t 3 2 1
Pair 3:
Multiply the gear ratios:
45:1

37. Team Unlimited’s 2-Speed Transmission

38. Calculate This:
60 tooth tooth 60 tooth
36 tooth tooth 60 tooth
Is this transmission currently geared up or down? → geared down
What is the current gear ratio of this transmission? → 60:36 = 5:3
What is the gear ratio of the other set of gears? → 60:60 = 1:1

39. Calculate This:
60 tooth tooth 60 tooth
36 tooth tooth 60 tooth
Is this transmission currently geared up or down? → geared down
What is the current gear ratio of this transmission? → 60:36 = 5:3
What is the gear ratio of the other set of gears? → 60:60 = 1:1

40. Sumo-Bot All robots are placed in a 10’ x 10’ field
If any part of a robot touches the field wall, it is removed
The last robot left on the field wins!

41. Hint: use gears to get the perfect combination of speed & torque
Good Luck!
Hint: use gears to get the perfect combination of speed & torque

42. Thanks/Resources Teaching Gear Theory to Students
CMU's Vex Curriculum: Gearbox Lesson