Gears & VEX
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
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? 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)?
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
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)?
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
Gear Types spur gears differential bevel gears rack & pinion worm gear
Spur Gears 12 tooth 24 tooth 84 tooth 36 tooth 60 tooth
Worm gears allow axles at right angles to transfer rotational motion.
Bevel gears allow rotational motion to be transferred at right angles.
Rack & Pinion pinion rack 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: same direction driver driver follower follower driver
Would the follower gear move clockwise or counterclockwise? Did you get it? driver Would the follower gear move clockwise or counterclockwise?
Would the follower gear move clockwise or counterclockwise? Did you get it? driver Would the follower gear move clockwise or counterclockwise?
Would the follower gear move clockwise or counterclockwise? Did you get it? driver Would the follower gear move clockwise or counterclockwise?
Would the follower gear move clockwise or counterclockwise? Did you get it? driver Would the follower gear move clockwise or counterclockwise?
Geared Up large driver turns small follower increases speed decreases torque (turning force) follower driver driven gear follower gear
Geared Down small driver turns large follower increases torque (turning force) decreases speed driver follower driven gear follower gear
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.
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
What is the gear ratio? 84 tooth driver 60 tooth follower
What is the gear ratio? driver follower
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
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
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
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
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
Calculate the Gear Ratio (Assume the last axle does the useful work) 4 12t 36t 3 2 1
Calculate the Gear Ratio (Assume the last axle does the useful work) Pair 1: 36t 12t 12t 4 12t 36t 3 2 1
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
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:
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
Team Unlimited’s 2-Speed Transmission
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? → 60:36 = 5:3 What is the gear ratio of the other set of gears? → 60:60 = 1:1
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? → 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!
Hint: use gears to get the perfect combination of speed & torque 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