Gears

1
Gears VEX
2
Agenda
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
motor

• Which gear is the driver (A or B)?
• Which gear is the follower (A or B)?

5
Do you get it?
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?
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?
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
Worm gears allow axles at right angles to
transfer rotational motion.
worm gear
11
Bevel Gears
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
follower

• even number of gears
• driver follower turn in
• opposite directions
• odd number of gears
• driver follower turn in
• same direction

driver
driver
follower
follower
driver
17
Did you get it?
driver
18
Did you get it?
driver
19
Did you get it?
driver
20
Did you get it?
driver
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
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
• ? or 13
• 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

• 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)

1. Pair up drivers and followers
2. Start a new driver/follower pair if an axle has a
   second gear attached.
3. 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)

1. Pair up drivers and followers
2. Start a new driver/follower pair if an axle has a
   second gear attached.
3. 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)

1. Pair up drivers and followers
2. Start a new driver/follower pair if an axle has a
   second gear attached.
3. 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)

1. Pair up drivers and followers
2. Start a new driver/follower pair if an axle has a
   second gear attached.
3. 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
151
32
Calculate the Gear Ratio(Assume the last axle
does the useful work)
60t
36t
12t
12t
4
12t
36t
3
2
1
33
Calculate the Gear Ratio(Assume the last axle
does the useful work)
60t
Pair 1
36t
12t
12t
4
12t
36t
3
2
1
34
Calculate the Gear Ratio(Assume the last axle
does the useful work)
60t
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)
60t
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)
60t
Pair 1
36t
12t
12t
4
Pair 2
12t
36t
3
2
1
Pair 3
Multiply the gear ratios
451
37
Example of2-Speed Transmission
38
Calculate This
60 tooth 36 tooth 60 tooth
36 tooth 60 tooth 60 tooth
Is this transmission currently geared up or down?
? geared down What is the current gear ratio of
this transmission? ? 6036 53 What is the
gear ratio of the other set of gears? ? 6060
11
39
Calculate This
60 tooth 36 tooth 60 tooth
36 tooth 60 tooth 60 tooth
Is this transmission currently geared up or down?
? geared down What is the current gear ratio of
this transmission? ? 6036 53 What is the
gear ratio of the other set of gears? ? 6060
11
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
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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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.

•  http//www.edinformatics.com/math_science/simple_
  machines/mechanical_advantage.htm
• http//www.uark.edu/depts/aeedhp/agscience/simpmac
  h.htm
• http//www.mikids.com/Smachines.htm
• http//images.google.com/images?hlenqsimple20m
  achines20wheel20and20axleum1ieUTF-8saNta
  bwi
• www.georgiactae.org/Curriculum20-20Unit20Plans/
  Engineering/.../STEM20Mini-Golf20Course/Simple2
  0Machines.ppt
• http//www.teachengineering.org/view_lesson.php?ur
  lhttp//www.teachengineering.org/collection/cub_/
  lessons/cub_simp_machines/cub_simp_machines_lesson
  03.xml
• http//www.beaconlearningcenter.com/WebLessons/Sim
  pleMachines/graphics/WandALabeled3.jpg