Gears & VEX
J.M. Gabrielse
J.M. Gabrielse
Agenda
gear testing
apparatus
•
•
•
•
•
•
Essential Terminology
Gear Types
Direction
Gearing Up/Gearing Down
Gear Ratios
Examples
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Essential Terminology
• Driver – gear attached to a motor
• Follower – 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
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Do you get it?
B
A
motor
• Which gear is the driver (A or B)?
• Which gear is the follower (A or B)?
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driver
Do you get it?
follower
B
A
motor
• Which gear is the driver (A or B)? → A
• Which gear is the follower (A or B)?
→
B
J.M. Gabrielse
Do you get it?
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)? J.M. Gabrielse
Do you get it?
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)? →J.M.
B Gabrielse
Gear Types
spur gears
differential
bevel gears
rack & pinion
X - not used by the Summer STEM Academy
worm gear
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Spur Gears
12 tooth
24 tooth
84 tooth
36 tooth
The number of teeth on each
spur gear is a multiple of 12.
12 = 1 x 12, 36 = 3 x 12,
60 = 5 x 12, 80 = 7 x 12
60 tooth
X - only works with the worm gear
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Rack & Pinion
pinion
rack
Racks and pinions are used to translate rotational motion into linear motion.
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Direction
• every time you add a gear the
direction reverses
follower
driver
• even number of gears:
driver & follower turn in
opposite directions
• odd number of gears:
driver & follower turn in
same direction
driver
follower
follower
driver
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Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?
J.M. Gabrielse
Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?
J.M. Gabrielse
Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?
J.M. Gabrielse
Did you get it?
driver
Would the follower gear move clockwise or counterclockwise?
J.M. Gabrielse
Geared Up
• large driver turns small follower
• less torque (turning force)
• more speed
follower
driver
driven gear
follower gear
J.M. Gabrielse
Geared Down
• small driver turns large follower
• more torque (turning force)
• less speed
driver
follower
driven gear
follower gear
J.M. Gabrielse
Gear Analysis
To analyze any gear train you need to:
1. Find the number of driver teeth
2. Find the number of follower teeth
3.
follower t eeth
gear ratio 
driver tee th
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Example
12 tooth driver
36 tooth follower
Gear Analysis
1. follower teeth: 36
2. driver teeth: 12
follower t eeth 36 3
gear
ratio



3.
driver tee th
12 1
– 3/1 or 3:1
– read as 3 to 1
– 3 turns of the driver will turn the follower 1 time
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What is the gear ratio?
84 tooth driver
60 tooth follower
J.M. Gabrielse
What is the gear ratio?
84 tooth driver
60 tooth follower
gear ratio 
follower t eeth 60 teeth 5


driver tee th
84 teeth 7
J.M. Gabrielse
Your Turn
What is the gear
ratio of the
Protobot?
60 tooth gear
60 tooth gear
J.M. Gabrielse
Your Turn
What is the gear
ratio of the
Protobot?
60 tooth gear
60 tooth gear
Gear Analysis
1. follower teeth: 60
2. driver teeth: 60
60 1

3. gear ratio 
60 1
J.M. Gabrielse
Thanks/Resources
• Inventor’s Guide: 3·19 - 3·13
• Teaching Gear Theory to Students
• CMU's Vex Curriculum: Gearbox Lesson
J.M. Gabrielse