Presentation on theme: "Gears. Gears are used in machines with spinning axles Several uses – To reverse the direction of rotation – To increase or decrease the speed of rotation."— Presentation transcript:
Gears are used in machines with spinning axles Several uses – To reverse the direction of rotation – To increase or decrease the speed of rotation – To move rotational motion to a different axis
To reverse the direction of rotation To increase or decrease the speed of rotation To move rotational motion to a different axis
Drawing Gears Drawing the teeth would be a problem Simply draw the inner and outer diameter circles
Spur Gears Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions. Spur gears are used in many devices like:- – the electric screwdriver, windup alarm clock, washing machine and clothes dryer. Very noisy so not used in cars (helical gears are used)
Watch the gears Gear Ratios Every time the larger gear goes around once, the smaller gear goes around twice. The diameter of the gear on the left is twice that of the gear on the right. – The gear ratio is therefore 2:1 (pronounced "two to one"). What would happen if both gears were the same size?
Gear Ratios Most gears that you see in real life have teeth. They make it possible to determine exact gear ratios. – e.g. one gear has 40 teeth and another has 10 teeth
Working out Gear Ratios Teeth on driven Teeth on driver Gear Ratio = Driver – is powered (connected to the motor) Driven – is driven by the driver Gear Ratio = = 4 1 Gear Ratio = 4 : 1 40 teeth 10 teeth driver driven Connected to motor i.e. For every 4 turns of the driver the driven turns once
Changing rotational speed Why bother? Motors tend to spin very quickly but without much torque! Whats torque?
Torque Torque is a force that tends to rotate or turn things. You generate a torque any time you apply a force using a wrench. Tightening the lug nuts on your wheels is a good example.
Wheel Wrench Pressing down on the wrench creates a turning force (torque) Push Down Creates rotation The same force is created between the wheel and the floor
Torque In a vehicle the rotational force is converted into forward motion Movement Higher torque allows more weight to be moved Force
Bicycle example Imagine riding a bike with gears Flat ground – high gear Gives high speed low torque uphill – low gear Gives low speed but high torque
Torque vs Speed Low speed with high torque High speed with low torque Good speed but easy to stop No point racing but very difficult to stop What does the sumobot need?
Large Ratios What if you wanted a reduction of speed of 100:1 ? With simple gear train – 1000 teeth on one gear 10 on the other This is silly! Teeth would have to be very small
Compound Gears Allows higher ratios to be created Put two gears on one shaft Two gears on one shaft
Compound Gears Several compound gears in a line the purple gear turns at a rate twice that of the blue gear. the green gear turns at twice the rate of the purple gear. the red gear turns at twice the rate as the green gear.
1 : 2 Overall 1 : 8 (2 x 2 x 2) Compound Gears
Sumobots Here is the gear train Motor drives Connected to wheel Split it up to work out the gear ratio Compound Gear Two gears on one shaft