| Intermediate Technology Education | Control Technology | Pre-Design | Topic 3 | Activity 4 |

Mechanical Systems

To develop understanding of mechanical systems as a form of control system.
  • Identify simple machines
  • Describe mechanisms
  • Identify mechanical control systems

Simple Machines

Simple machines are the basic machines defined by science.  They are the lever, inclined plane, wheel and axle, wedge, pulley and the screw.  Simple machines are used to gain mechanical advantage.  That is, the force required to move a load can be less that weight of the load.  In exchange you have to apply the force over a greater distance than the vertical motion of the load. 

Levers

Levers are a class of simple machine used to move loads with different amounts of force, depending on the location of the fulcrum.  There are 3 types (classes) of lever.  In the figures below, D1 is the distance from the fulcrum to the load, and D2 is the distance from the fulcrum to the force required to move it.


Figure Class 1 Lever

Figure Class 2 Lever

Figure Class 3 Lever

In the case of the class 3 lever, can the force ever be less than the load?

Here are simple examples of levers


Figure Class 1 Lever

Figure Class 2 Lever

By moving the fulcrum, you can control the amount you can lift with the same effort.  The three classes are demonstrated in the following video clip


Video Levers

Inclined Plane

An inclined plane is simply a sloped surface.  A load can be slid along the inclined plane to move it a vertical distance.  By adjusting the slope of the plane, you can control how much force it takes to move the load.  The lower the slope, the less force is required, but the longer the distance it has to be moved to get the same vertical rise.


Figure Inclined Plane

The picture below illustrates one use of an inclined plane. 


Figure Application of the Inclined Plane

Wheel and Axle

The wheel and axle appear in all sorts of equipment, from toys to industrial machines.  The load may be at the axle or at the rim of the wheel.  Which one requires less force than the load?


Figure Wheel and Axle showing Possible Applications of Load and Force

Figure Wheel and Axle

Wedge

The wedge is essentially a pair of inclined planes.  It moves a load that is at right angles to the force


Figure The Wedge

The wedge has many uses, especially for cutting tools. All knives, saws, planes and chisels use the wedge for cutting.  A few are illustrated below.


Figure Objects using a Wedge Shape

Pulley

Pulleys are essentially wheels with hollowed out rims.


Figure Pulleys

Figure Typical Plastic Pulleys

Pulleys are freewheeling on their axles.  Mechanical advantage is only obtained if they are combined in multiples in a block, with two blocks of pulleys used.  In the figure below, you can see the progression from pulleys to block to two blocks. This configuration can produce large mechanical advantages.


Figure Application of Pulleys

Screw

The screw is an inclined plane wrapped around a cylinder.


Figure Screw as Inclined Plane

Figure Typical Screws and A Bolt

Mechanisms

Mechanisms are devices made from combinations of simple machines.  A few examples of geared mechanisms follow.  Gears are essentially wheels with teeth.  The teeth give a positive lock from one gear to another and prevent slipping.


Figure Gear Train from a Gear Box.  Note the Drive Motor with the White Gear

Figure Use of a Pinion Gear To Change direction of Rotation by 900

Figure Complete Gear Train

Figure Gearbox with Planetary Gears

Here are a few small tools that are based on simple machines.  Can you identify all the simple machines employed in each mechanism?


Figure Coax Connector Crimper and Wire Stripper

Figure Ratchet and Pliers

Figure Sheet Metal Nibbler

Figure Rabbeting Plane

Figure Assorted Tools for Sewing

Control Mechanisms

Mechanical control mechanisms are used to start and stop, open and close, regulate speed and so on.  For example

  • Door knobs and locks translate rotary motion into linear motion,
  • Bicycle gears and derailleurs allow you to change gear ratios and therefore speed of the bike,
  • Levers allow you to open and close hoppers in machines, even simple ones like fertilizer spreaders
  • Step pulleys and variable speed pulleys allow you to change the speed of machinery, as in the following video clip. 

Video Pulleys

More Information

For more information check these pages

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