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

Gears & VEX

Agenda

• Essential Terminology• Gear Types• Gearing Up/Gearing Down• Direction• Gear Ratios• Example• Application: Sumo-Bot Competition

gear testing apparatus

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

Do you get it?

• Which gear is the driver (A or B)?

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

A B

motor

Do you get it?

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

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

A B

motor

Do you get it?

• 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)?

A B C

motorwheel

Do you get it?

• 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

A B C

motorwheel

Gear Types

spur gears

differential bevel gears rack & pinion worm gear

Spur Gears

84 tooth

60 tooth

36 tooth

24 tooth

12 tooth

Worm Gears

worm gear

Worm gears allow axles at right angles to transfer

rotational motion.

Bevel Gears

Bevel gears allow rotational motion to

be transferred at right angles.

Rack & Pinion

rack

pinion

Racks and pinions are used to translate rotational motion into linear motion.

Differential

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

Sprockets & Chains

Sprockets inside the same chain rotate in the same direction.

Sprockets outside the chain rotate in the opposite direction.

Pulleys & Belts

Pulleys and belts are not available for VEX

Sometimes tank treads can be used as belts.

Direction

• even number of gears:

driver & follower turn in

opposite directions

• odd number of gears:

driver & follower turn in

same direction

driver

driver

driver

follower

follower

follower

Did you get it?

driver

Would the follower gear move clockwise or counterclockwise?

Did you get it?

driver


Did you get it?

driver


Did you get it?

driver


Geared Up

• large driver turns small follower

• increases speed• decreases torque

(turning force)

driven gear follower geardriver

follower

Geared Down

• small driver turns large follower

• increases torque (turning force)

• decreases speed

driven gear follower gear

follower

driver

Gear Analysis

To analyze any gear train you need to:

1. Locate the driver gear

2. Locate the follower gear

3. Calculate the Gear Ratio

Use the following rules to calculate gear ratios.

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

thdriver tee

eethfollower t ratiogear

What is the gear ratio?

84 tooth driver

60 tooth follower

What is the gear ratio?

driver

follower

7

5

teeth84

teeth60

thdriver tee

eethfollower t ratiogear

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!

DriverIdlers

Follower Gear Ratio = 24/40

= 3/5

3 turns of the 40 tooth gear will turn the 24 tooth gear 5 times.

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






D2



Gear 1 & Gear 2:

1

3

12

36

driver

follower





1

15

1

5x

1

3

D2



Gear 1 & Gear 2:

Gear 3 & Gear 4:

1

3

12

36

driver

follower

1

5

12

60

driver

follower

Multiply the gear ratios:





1

15

1

5

1

3

D2



Gear 1 & Gear 2:

Gear 3 & Gear 4:

1

3

12

36

driver

follower

1

5

12

60

driver

follower


15:1

Calculate the Gear Ratio(Assume the last axle does the useful work)

36t

36t

60t

12t

12t

1 23

4

12t


36t

36t

60t

12t

12t

1 23

4

Pair 1:

1

3

12

36

driver

follower

12t


36t

36t

60t

12t

12t

1 23

4

Pair 1:

1

3

12

36

driver

follower

1

3

12

36

driver

follower

Pair 2:

12t


36t

36t

60t

12t

12t

1 23

4

Pair 1:

Pair 3:

1

3

12

36

driver

follower

1

5

12

60

driver

follower

1

3

12

36

driver

follower

Pair 2:

12t


36t

36t

60t

12t

12t

1 23

4

1

45

1

5

1

3

1

3

Pair 1:

Pair 3:

1

3

12

36

driver

follower

1

5

12

60

driver

follower


1

3

12

36

driver

follower

Pair 2:

45:1

12t

Team Unlimited’s2-Speed Transmission

Calculate This:

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

60 tooth 36 tooth 60 tooth


Calculate This:

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



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!

Good Luck!

Hint: use gears to get the perfect combination of speed & torque

Thanks/Resources

• Teaching Gear Theory to Students

• CMU's Vex Curriculum: Gearbox Lesson

http://first.wpi.edu/Images/CMS/First/2005CON_Teaching_Gear_Theory_to_Students.ppt

http://www.education.rec.ri.cmu.edu/roboticscurriculum/vex_online/lessons/gearbox/lesson.html

Documents

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