Core 1.5 Mechanisms

Core 1.5 Mechanisms

1. 1.5.7 Cranks and Sliders

2. 1.5.8 Gear Types

   • Simple and Compound Gear Train
     • Better than pulley systems - prevents slippage
   • Idler
     • B in the diagram to the right is an idler gear. A is  the driver and C is the driven gear in this gear train.
   • Bevel gears
     • Transfer motion at 90 degrees.
   • Rack and Pinion
     • Used for things like lowering systems, and funicular railways.
   • Revolutions per minute (RPM)
     • Output speed = input speed/gear ratio
   • Gear Ratios
     • Number of teeth on driven gear/Number of teeth on driver gear

3. 1,5.6 Pulleys and Belts

   • Input and Output
   • Velocity ratio (V.R.)
     • VR = Driven pulley diameter/Driver pulley diameter
   • V-belt
     • http://www.technologystudent.com/pdf14/poster_pulley1.pdf

4. 1.5.2 Classification of Levers

   • Levers
     • 1
     • 2
     • 3
   • Calculations
     • MA
       • Allows a large force to be exerted with small effort.
         • MA = Load/Effort
     • VR
       • The Ratio of the distance the effort has to move compared to the load.
         • VR = Distance moved by effort/Distance moved by load
     • Load
       • The force exerted by the load
     • Efficiancy
       • The relationship between Input Force and movement
         • No mechanism is 100% efficient
           • Efficiency = MA/VR x 100%
     • Effort
       • The amount of force put in by the user
     • Torque
       • A measure of a system's turning power
         • Measured in Newton Meters or Lb Ft (Foot-Pounds; the amount of turning force required to move a pound one foot)

5. 1.5.3 Linkages

   • Bell crank
     • The light blue mechanism is the Bell crank in these illustrations.
     • Transfers movement at 90 degrees.
   • Reverse motion linkages
     • Parallel Motion Linkages are basically coupling rods from a steam train.

6. 1.5.4 Cams

   • Pear shaped
     • Motionless (Dwells) about half the cycle
   • Drop (snail)
     • If you reverse with a snail cam, you will break the mechanism.
     • Slow rise, then a sudden drop
   • Eccentric (circular)
     • Gives smooth, continuous movement

7. 1.5.5 Followers

   • Flat followers
     • Prone to friction
   • Knife
     • Used when accuracy is require (Embroidery machine), as the profile of the cam is precisely followed.
   • Roller
     • Better when higher speeds are required

8. 1.5.1 types of Movement

   • Linear
   • Reciprocation
   • Rotary
   • Oscillation

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