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. Example of 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

43. Glossary of gears and other terms used for machines
Read by yourself

44. Glossary Gear and bearing assemblies Gear train Gears
Assembly drawings that show the parts of the complete mechanism, as they appear assembled.
Gear train
An arrangement of two or more gears connecting driving and driven parts of a machine.
Gears
Toothed wheels used to transmit motion and power from one shaft to another.

45. Glossary Heavy bearings Intersecting shafting gears Involute curve
Bearings often designed for special service where extra heavy shock loads are required.
Intersecting shafting gears
Allow for the change in direction of motion from the gear to the pinion.
Involute curve
A spiral curve generated by a point on a chord as it unwinds from the circle.

46. Glossary Light bearings Lobed ring seal Cluster gears
Bearings generally designed to accommodate a wide range of applications involving light to medium loads combined with relatively high speeds.
Lobed ring seal
A seal with rounded lobes that provide additional sealing forces over the standard O-ring seal.
Cluster gears
Two or more spur gears cut on a single shaft.

47. Glossary
Labyrinth
A seal that is made of a series of spaced strips that are connected to the seal seat, making it difficult for the lubrication to pass.

48. Glossary Mechanism Medium bearings Miter gears
An arrangement of parts in a mechanical device or machine.
Medium bearings
Bearings with heavier construction than light bearings, and provide a greater radial and thrust capacity.
Miter gears
The same as bevel gears, except both the gear and pinion are the same size and are used when shafts must intersect at 90° without speed reduction.
Diametral Pitch
A ratio equal to the number of teeth on a gear per inch of pitch diameter.

49. Glossary Molded lip packings Molded ring seals
Provide sealing as a result of the pressure generated by the machine fluid.
Molded ring seals
Seals placed in a groove and provide a positive seal between the shaft and bearing or bushing.
Nonintersecting shafting gears
Gears with shafts that are at right angles but not intersecting.

50. Glossary O-ring seal Plate cam Pressure angle Pulley
The most commonly used seal because of its low cost, ease of application, and flexibility.
Plate cam
A cam in the shape of a plate or disk. The motion of the follower is in a plane perpendicular to the axis of the camshaft.
Pressure angle
The direction of push transmitted from a tooth on one gear to a tooth on the mating gear or pinion.
Pulley
A wheel with a flat, convex, or grooved rim mounted on a shaft and driven by a belt or other means.

51. Glossary Rack Sealed bearing
A straight bar with spur teeth used to convert rotary motion to reciprocating motion.
Sealed bearing
A bearing with seals made of rubber, felt, or plastic placed on the outer and inner rings of the bearing. The sealed bearings are filled with special lubricant by the manufacturer.

52. Glossary Shield Splines Gaskets Gear
A metal plate on one or both sides of the bearing that acts to keep the bearing clean and retain the lubricant.
Splines
Teeth cut in a shaft and a gear or pulley bore and are used to prevent the gear or pulley from spinning on the shaft.
Gaskets
Seals made from materials that prevent leakage and access of dust contaminants into the machine cavity.
Gear
A cylinder or cone with teeth on its contact surface; used to transmit motion and power from one shaft to another.

53. Glossary End thrust Felt seals and wool seals
A lateral force exerted on the end of the gear shaft.
Felt seals and wool seals
Seals used where economical cost, lubricant absorption, filtration, low friction, and a polishing action are required.

54. Glossary Static sealing Timing
Stationary devices that are held in place and stop leakage by applied pressure.
Timing
The regulation of occurrence, rate, or coordination of a mechanism, such as the synchronization of the rotation of a cam to achieve a desired effect.

55. Glossary Dynamic seals
Seals, such as packings, that contact the moving parts of the machinery.

56. Work Citied Page I used all the websites that are listed here….