Mechanical Devices Flashcards
Mechanism
A mechanism is a device that changes an input motion into a different output motion
Examples of mechanisms
- levers
- linkages
- cams
- gear trains
- pulleys and belts
Types of motion
- linear (straight line)
- rotary (round)
- oscillating (movement swinging from side to side)
- reciprocating (movement backwards and forewords in a straight line)
3 main points of a lever
- effort (input)
- load (output)
- pivot/fulcrum
Lever
A rigid bar that turns around a fulcrum
Three classes of lever
First class Second class Third class
First class
When the fulcrum is at the middle eg. crowbars
Second class
When the load is in the middle eg. wheel burrow
Third class
When the effort is in the middle eg. cranes, fishing
Arm length
The distance between the fulcrum and the effort/load
Linkages
A collection of levers
What can cams and followers do
A cam and a follower convert rotary motion into reciprocating motion
Pear
Pear shaped
Eccentric
Shaft is not in middle
Snail
Looks like a snail’s shell
Four lobed
Looks like a shuriken
Shaft, follower, slider, cam
The pivot, the stick that goes up and down, the piece that keeps the follower in place, the rotating shape
Driver (gear)
The one closer to the input
Driven (gear)
The one further away from the input
Scale of gears
Spur gear (one gear) -> gear train (pair of gears)-> gear box (more than 2 gears)
The smaller gear moves … than a larger gear
Faster
Direction of gears
Any 2 gears adjacent to each other rotates in the opposite direction
What is put onto gears in order to lubricate it
Oil, grease, graphite, PTFE
Pulleys
A wheel with a groove in its rim
Belt
A flexible belt connecting 2 pulleys together
Why do you use 2 different sized pulleys?
To either increase or decrease the speed of rotation and increase or decrease the torque (turning force) transmitted
