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Think about a bicycle, an eggbeater, a sewing machine, a hand cranked drill, and a workshop vice. What do they have in common? All of them have at least one mechanism that provides movement. Some of the devices use human effort, while others use electricity. If the devices were taken apart, you would find a series of gears that redirect the applied force so they can accomplish their tasks. Gears come in all sizes. Small gears are found in mechanical watches, while very large gears are found in cranes that are used to raise large bridge sections into place. Some of the gears are encased in covers to protect them from their surroundings, while others are left out in the open.
The activities in this lesson will introduce you to several mechanisms that are used to change speed, torque, force, type of movement, and direction of movement. These mechanisms have been developed over time to address the need for changes in machine tools, robots, automobiles, airplanes, etc. You will build different mechanisms and discover how they are used in the world today. You will be introduced to the VEX® building parts and the proper way to assemble them. It will be important you learn to correctly assemble and disassemble the parts so that they are not damaged.
Mechanisms
Mechanisms
A mechanism is a device that transmits movements so that the output movement is different than the input movement. It can be used to change the direction, speed, force, or type of movement. The output of a robot or any machine is motion and force in some form. A drill press, for example, has two kinds of motion: rotary and linear. The drill spinning provides the rotary motion; moving the drill down through the material is the linear motion. The force or torque applied to the drill must be sufficient to turn the drill through the material. Also, the speed of the drill bit must be within a given range. If the drill is turning too fast, the drill bit will be damaged. To acquire the correct speed, the drill press must have a pulley or gear system. Changing pulleys changes the speed of the drill bit.
Gears
Gears
When you are riding a multi-speed bicycle up a steep hill, what do you do? Most likely you shift gears in order to get more power with the same amount of effort. Sometimes when a standard shift or four-wheel drive vehicle is being driven up a steep incline, the driver will downshift or engage the four-wheel drive in order to gain more torque. Can you think of other examples where force or torque is changed to make a task easier?
Key Concepts:
1. Energy is the capacity to do work.
2. Engineers and technologists design mechanisms to change energy by transferring direction, speed, type of movement, and force or torque.
3. Mechanisms can be used individually, in pairs, or in systems.
Key Terms
Key Terms
Belt and Pulley
The transmission of power between shafts by means of a belt connecting pulleys on the shafts.
Bevel gear
One of a pair of gears used to connect two shafts whose axes intersect.
Chain
A connected flexible series of links used for fastening or securing objects and pulling or supporting loads.
Crank and Slider
A pivot pin near the outside edge of a wheel or disk that changes rotary motion into reciprocating motion.
Drive Gear
The gear which transmits power and motion to the rest of the system. The input gear.
Driven Gear
The member of a pair of gears to which motion and power are transmitted by the other. The output gear.
Energy
The ability to do work.
Force
A push or pull on an object.
Gear
A toothed wheel that works with others to alter the relation between the speed of an engine and the speed of the driven parts.
Gear Ratio
The ratio of the speed of the driving member of a gear train to that of the driven member.
Idler Gear
A gear between the driver and the driven gear used to change rotational direction.
Input
Something put into a system, such as resources, in order to achieve a result.
Linear Motion
Movement in a straight line.
Mechanism
The part of a machine which contains two or more pieces arranged so that the motion of one compels the motion of the others.
Oscillate
A swing back and forth at a regular rate.
Output
The results of the operation of any system.
Pitch
The distance between adjacent threads in a screw.
Rack and Pinion
A rotating gear that meshes with a bar that has gear teeth along its length. Changes rotating motion into linear motion.
Reciprocating
A back and forth movement.
Rotary Motion
Circular movement.
Simple Gear Train
A combination of two or more gears used to transmit motion between two rotating shafts or between a shaft and a slide.
Sprocket
Toothlike projections arranged on a wheel rim to engage the links of a chain.
Torque
A twisting force.
Worm and Wheel
A mechanical arrangement consisting of a toothed wheel driven by a short revolving cylinder bearing a screw thread.
Assignment 1: Mechanical Systems Google Doc
Directions: Use this site to complete the Mechanical Systems Assignment (Your copy found in schoology)
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