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Gears & V E X. 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

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## Gears & V E X

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**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)? B A motor**Do you get it?**• Which gear is the driver (A or B)? →A • Which gear is the follower (A or B)? →B B A 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)? wheel motor A B C**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 wheel motor A B C**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**Worm gears allow axles at right angles to transfer rotational motion. worm gear**Bevel Gears**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**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**Would the follower gear move clockwise or counterclockwise?**Did you get it? driver**Would the follower gear move clockwise or counterclockwise?**Did you get it? driver**Would the follower gear move clockwise or counterclockwise?**Did you get it? driver**Would the follower gear move clockwise or counterclockwise?**Did you get it? driver**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**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**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) 60t 36t 12t 12t 4 12t 36t 3 2 1**Calculate the Gear Ratio(Assume the last axle does the**useful work) 60t Pair 1: 36t 12t 12t 4 12t 36t 3 2 1**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**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:**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: 45:1**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**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!**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

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