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Simple Machines: Gears, Velocity Ratios and Mechanical

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Simple Machines: Gears, Velocity Ratios and Mechanical Advantage What is a simple machine? A device which uses basic mechanisms to make work easier for the user. – PowerPoint PPT presentation

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Title: Simple Machines: Gears, Velocity Ratios and Mechanical


1
Simple Machines Gears, Velocity Ratios and
Mechanical Advantage
2
What is a simple machine?
  • A device which uses basic mechanisms to make work
    easier for the user.
  • Example Lifting a heavy box with a rope and
    pulley system
  • Simple machines are found in many transportation
    devices such as the following
  • Cars
  • Bicycles
  • Trains

3
What are gears and why are they so useful?
  • Gears are toothed wheels which interlock to form
    simple machines.
  • The tighter the joint, the less chance of
    slipping
  • Gears range in size but the important number is
    how many teeth a gear has.

4
What is a gear ratio?
  • A gear ratio is the ratio between the driver gear
    (the one being powered) and the driven gear (the
    one connected to the driver)
  • Gear Ratios are expressed as fractions and can be
    written a number of ways.
  • 1 to 3
  • 1/3
  • 13
  • Always remember that the driven gear will turn in
    the opposite direction of the driver gear

5
What is a pulley?
  • A wheel with a grove carved around its
    circumference in which a rope or belt is placed
    to drive the wheel.
  • Pulleys are used in a number of applications
    including
  • Elevators
  • Cranes
  • Automobiles

6
A Pulley System
7
Drawbacks of Pulleys
  • Pulleys work great as long as the belt which
    connects them is tight and both pulleys are
    aligned.
  • Pulleys tend to slip when too much strain is
    placed on the system.

8
How do I calculate my gear ratio?
  • A simple equation is used to find the ratio of
    your gearing system
  • Number of Teeth on the Driven Gear / Number of
    Teeth on the Driver Gear.
  • Size of the driver pulley/ Size of the driven
    pulley

9
What is Velocity Ratio (VR)?
  • When calculating for velocity or speed, it is
    best to have a ratio in which the driver gear is
    larger than the driven gear.
  • For maximum speed you should always have a larger
    driver gear/pulley paired with a smaller driven
    gear/pulley.

10
What is Mechanical Advantage (MA)?
  • Reciprocal of velocity ratio.
  • Mechanical advantage describes how much work can
    be done based on the input.
  • If my system required me to apply 50 pounds of
    force into the system to lift 100 pounds of
    weight, I have used MA.

11
So which do I want?
  • Higher velocity ratios are better when working on
    straight and level surfaces which are smooth.
  • Always remember that with a high VR your system
    will have very low power.
  • Higher mechanical advantage systems are better
    with inclines surfaces that are bumpy.
  • With a high MA your system will produce more
    power, but will move slower.
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