Presentation on theme: "GEARS Gears and shafts are basically wheel and axles, but gears have cogs, or teeth on their circumference."— Presentation transcript:
1 GEARSGears and shafts are basically wheel and axles, but gears have cogs, or teeth on their circumference.
2 GEARSGears turn either clockwise or counter- clockwise. When gears touch, we call it meshing. As gears mesh, they turn in opposite directions.
3 GEARSIn multiple gear sets, all odd numbered gears turn the same direction, and the even numbered gears turn in the opposite direction.
4 GEARSTo make two gears turn in the same direction, (A & C) another gear (B) needs to be between the two. This gear, without a load, is called the idler. It can be any size, or there can be multiple idler gears.CAB
5 GEARS Gears are generally used for one of four different reasons: To reverse the direction of a rotational force.To increase or decrease the speed of rotation.To move rotational motion to a different axis.To keep the rotation of two axis synchronized.
6 GEARSAnother option exist with a rack and pinion gear set. Rack and pinions convert rotary motion to linear motion.
7 GEARSBevel gears can change the direction of the rotational axis.
8 GEARSWorm gears are like screws. They prevent slippage, and reduce rotational speed and increase torque.
9 GEARSPlanetary gears utilize a system that consists of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear.
10 GEARSA common example of this type of gearing system is the manual pencil sharpener. In this instance, the planet gear is stationary and the sun gear moves.
11 GEARSAnother way to make two gears turn the same direction is to use a chain. The gears are shaped a little different, and are called sprockets. Advantages include greater distance between gears, a greater tolerance for alignment, and less damage to the system should a chain break.
12 GEARSConservation of energy requires that the amount of power delivered by the output gear or shaft will never exceed the power applied to the input gear, regardless of the gear ratio.
13 GEARSActual output will never reach theoretical outputs due to friction, errors, entropy, or any number of other external forces or situations involved.
14 GEARSGear = # of Teeth on Driven Gear Ratio # of Teeth on Driving Gearexample: 35 = 7The 60 teeth gear will spin 7 times, while the 35 teeth gear will spin 12 times.6035
15 GEARSCompound Gears are gears consisting of two gears turning on the same axle. The have the same rate of rotation.
16 GEARSGear ratios for each individual gear pair are multiplied together to compute the overall compound gear ratio.
17 GEARS Example: Gear ratio between A and B is 12:36 or 1:3. The gear ratio between C and D is 12:60 or 1:5Overall gear ratio is 1/3 x 1/5 = 1:15. A will spin once for D to spin 15 times.
18 GEARSTorque is rotational force. Torque is often talked about in using it to drive in screws, fasten nuts onto bolts and other such activities.
19 GEARSTorque = Force x Lever Arm (distance between force and the objects center of mass) [In our case, the radius of the wheel]. Formula: t = f x L
20 GEARSTorque is measured in the relationship between the measurements used in determining force and length, i.e. torque is measured in foot- pounds if the force is lbs. and the distance feet; or Newton – meters if Newton and meter are used; inch-ounces if these two force and distance measurements are used.
21 GEARSThe relationship between torque, gear ratio, speed, etc. increases or decreases on a linear scale. This could be either a direct relationship (as gear ration increases from 1:3 to 1:5 speed increases) or an indirect or inverse relationship, (torque decreases as speed increases.) As a consequence, more torque = less speed and vise-versa.
22 GEARSWhen gears mesh, both gears exert the same amount of force in opposite directions at any given point.
23 GEARSIf a driving gear of 60 teeth is meshed with a driven gear of 36 teeth, then the force where the two gears meet is equal to f36 = f60. Torque ratio is therefore equal to the gear ratio.
24 GEARSSafety must be a consideration when working with gears. Extreme pressure can cause gears to shatter or strip out teeth. Pinching hazards exist as well.