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

Example of 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

Glossary of gears and other terms used for machines Read by yourself

Glossary Gear and bearing assemblies Gear train Gears 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.

Glossary Heavy bearings Intersecting shafting gears Involute curve 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.

Glossary Light bearings Lobed ring seal Cluster gears 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.

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.

Glossary Mechanism Medium bearings Miter gears 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.

Glossary Molded lip packings Molded ring seals 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.

Glossary O-ring seal Plate cam Pressure angle Pulley 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.

Glossary Rack Sealed bearing 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.

Glossary Shield Splines Gaskets Gear 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.

Glossary End thrust Felt seals and wool seals 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.

Glossary Static sealing Timing 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.

Glossary Dynamic seals Seals, such as packings, that contact the moving parts of the machinery.

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/simpmach.htm http://www.mikids.com/Smachines.htm http://images.google.com/images?hl=en&q=simple%20machines%20wheel%20and%20axle&um=1&ie=UTF-8&sa=N&tab=wi www.georgiactae.org/Curriculum%20-%20Unit%20Plans/Engineering/.../STEM%20Mini-Golf%20Course/Simple%20Machines.ppt http://www.teachengineering.org/view_lesson.php?url=http://www.teachengineering.org/collection/cub_/lessons/cub_simp_machines/cub_simp_machines_lesson03.xml http://www.beaconlearningcenter.com/WebLessons/SimpleMachines/graphics/WandALabeled3.jpg