Quick-fire: If an open ended question has multiple ways of solving the problem, what is a closed ended question? Give one example

Gears and Pulleys Aim: How can basic mechanical concepts improve our robot designs?

Goals Discuss the various gears found in the Lego Mindstorms kit Determine gear ratios, and understand how they can be used to improve designs Discuss other mechanical concepts, such as friction, work, and torque Understand the functions of belts and pulleys

Mechanical Advantage Factor by which a mechanism multiplies the force put into it Simple machines that produce MA: –Beam and Fulcrum –Wheel and Axle –Gears –Pulleys These simple machines can significantly increase our robots’ capabilities

Gears Gears are wheels with teeth which are used to transmit motion Gears can be meshed together to… –Produce more torque at a slower speed –Produce less torque at a greater speed –Change direction of rotating axles

Spur Gears Only mesh correctly if they are fitted to parallel axles Identified by number of teeth –8t, 16t, 24t, 40t

Vertical Matching of Gears For gears to be matched vertically, they should be separated by a combination of beams and plates

Gear Ratios Relationship between the number of teeth on two gears that are meshed –Indicates factor of speed or torque gained Driver Gear – initial source of motion (motor or manual) Follower Gear – motion is transferred to Gear Ratio = # of Teeth on Driver to # of teeth on follower Ex: 40 teeth 8 teeth 8:40, or 1:5

Examples – Gear Ratios 8:24, 1:3 24:40

Gearing Up When a driver gear has more teeth than the follower, it causes an increase in velocity –The follower makes more full rotations than the driver Price paid for higher gear ratios: –Decrease in torque, or strength

Example – Gearing Up Driver – 24-tooth gear Follower – 8-tooth gear Gear Ratio = Driver:Follower = 24:8, 3:1 Follower moves 3 times faster than driver

Gearing Down When a follower gear has more teeth than the driver, it causes an increase in torque –The follower makes fewer full rotations than the driver Price paid for higher gear ratios: –Decrease in speed –More friction

Example – Gearing Down Driver – 24-tooth gear Follower – 40-tooth gear Gear Ratio = 24:40, 3:5 Follower makes 3 revolutions each time the driver makes 5 revs Follower Driver

Bicycle Gears What role do gears play on a bicycle? How do gear ratios apply to riding a bike uphill or downhill?

Rack and Pinion Rotational force (and motion) is converted into linear force (and motion) Commonly found in automobile steering mechanisms

Bevel and Crown Gears Teeth are perpendicular to plane of the gear Allows you to transmit motion toward a new direction using a minimal amount of space Same gear ratio formula applies

Example – Bevel Gears Driver – 24-tooth Follower – 16-tooth Gear Ratio = 24:16, 3:2 24-tooth driver 16-tooth follower

Worm Gear Resembles a screw –Is a 1t gear – allows for high gear ratios –Worm can move spur, spur is locked

Examples – Worm Gear

Idler Gears Idler gears are typically inserted between two gears of the same size How many rotations of the first 8-tooth gear does it take to rotate the 3 rd gear? –1–1 –Idler gears do not change the gear ratio Idler gear They are intended for spacing

Belts and Pulleys Belts are used to link rotating pulleys –Transmits power very efficiently Pulleys can be used reduce the amount of force needed to lift a load –More wheels = less force, more friction

Friction Friction is the force between two surfaces rubbing together –It is an opposing force on a moving object Examples: –Walking on floor with more friction prevents slipping –In a car engine, inside wheel axles – will slow a car down, wear out parts

Pulley Ratios Pulleys do not have teeth for us to count to determine the speed/torque ratio between them How could we determine a ratio between them? –Diameter –Pulley Ratio = Driver:Follower Diameter

Examples – Pulley Ratio 1:1 Medium Pulley:Half Bushing 4:1