# Gears in VEX, examples and simple theory

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

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

5. Do you get it? A B 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 driver opposite directions • odd number of gears: driver follower driver & follower turn in same direction follower driver

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

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

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

20. 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. 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.

24. Gear Ratios (determining what a gear will do) follower teeth gear ratio  driver teeth 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 follower teeth 60 teeth 5 gear ratio    driver teeth 84 teeth 7

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 Idlers gear 5 times. 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: follower 36 3   driver 12 1 D2 Gear 1 = 12 teeth Gear 2 = 36 teeth Gear 3 = 12 teeth Gear 4 = 60 teeth