1. Gears & VEX
Adapted: Dec 2015 HEP

2. Agenda Essential Terminology Gear Types Direction
gear testing apparatus
Essential Terminology
Gear Types
Direction
Gearing Up/Gearing Down
Gear Ratios
Examples

3. Essential Terminology
Driver – gear attached to a motor
Follower (driven) – gear doing useful work
Idler – gear between the driver and follower
Geared Up – the follower moves faster than the driver
Geared Down – the follower moves slower than the driver

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 driven (A or B)?

5. Do you get it? B A Which gear is the driver (A or B)? → A
driven 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 driven (A, B, or C)?
wheel
motor A B C
Which gear is the driven (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
X - not used at this time

9. 24 tooth - only works with the worm gear
Spur Gears
12 tooth
24 tooth
84 tooth
36 tooth
60 tooth
The number of teeth on each spur gear is a multiple of 12.
12 = 1 x 12, 36 = 3 x 12, = 5 x 12, 80 = 7 x 12
24 tooth - only works with the worm gear

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

11. Direction every time you add a gear the direction reverses
even number of gears:
driver & follower turn in
opposite directions
odd number of gears:
same direction
driven
driver
driver
driven
driven
driver

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

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

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

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

16. Geared Up large driver turns small follower (driven)
less torque (turning force)
more speed
driven
driver
driver gear
driven gear

17. Geared Down small driver turns large follower (driven)
more torque (turning force)
less speed
driver
follower
driven gear
follower gear

18. Gear Analysis To analyze any gear train you need to:
Find the number of driver teeth
Find the number of driven teeth

19. Example 12 tooth driver 36 tooth follower Gear Analysis
follower teeth: 36
driver teeth: 12
3/1 or 3:1
read as 3 to 1
3 turns of the driver will turn the follower 1 time

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

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

22. Your Turn What is the gear ratio of the Protobot? 60 tooth gear

23. Your Turn What is the gear ratio of the Protobot? Gear Analysis
60 tooth gear
60 tooth gear
Gear Analysis
follower teeth: 60
driver teeth: 60

24. Thanks/Resources Inventor’s Guide: 3·19 - 3·13
Teaching Gear Theory to Students
CMU's Vex Curriculum: Gearbox Lesson