Intermittent MotionIntermittent motion is motion which starts and stops regularly. For example, in a cinema projector the film needs to be moved on one frame at a time then held stationary while the light projects it onto the screen. This is usually done with a geneva stop as shown here.Intermittent motion is usually the end result of a mechanism rather than the starting point for conversion.

Motion

Levers are an essential part of many mechanisms. They can be used to change the amount, the strength and the direction of movement. The position of the force and the load are interchangeable and by moving them to different points on the lever, different effects can be produced. The fixed point of the lever about which it moves is known as the fulcrum. In this example the force and the load move in opposite directions. With the force three times closer to the fulcrum them the load lifted is only one third of the force but it move three times as far.

Increase/Decrease Intermittent Motion

“Lever”

First order lever. Like a see-saw or balance, the load and the force are seperated by the fulcrum. As one moves up the orther moves down. The amount and the strength of the movement is proportianal to the distance from the fulcum

Increase/Decrease Intermittent Motion

“Lever”

Second order lever. A wheel barrow is a second order lever. Here the load is between the force and the fulcrum. This uses mechanical advantage to ease lifting of a large weight.

Increase/Decrease Intermittent Motion

“Lever”

Third order lever.Here the force is between the fulcrum and the load. Mechanical advantage is reduced but the movement at the load point is increased.

Increase/Decrease Intermittent Motion

“Lever”

Gears are used to change speed in rotational movement. In the example above the blue gear has eleven teeth and the orange gear has twenty five. To turn the orange gear one full turn the blue gear must turn 25/11 or 2.2727r turns.Notice that as the blue gear turns clockwise the orange gear turns anti-clockwise.In the above example the number of teeth on the orange gear is not divisible by the number of teeth on the blue gear. This is deliberate. If the orange gear had thirty three teeth then every three turns of the blue gear the same teeth would mesh together which could cause excessive wear. By using none divisible numbers the same teeth mesh only every seventeen turns of the blue gear.

“Gears”

Increase/Decrease Intermittent Motion

Gears are used to change speed in rotational movement. In the example above the blue gear has eleven teeth and the orange gear has twenty five. To turn the orange gear one full turn the blue gear must turn 25/11 or 2.2727r turns.Notice that as the blue gear turns clockwise the orange gear turns anti-clockwise.In the above example the number of teeth on the orange gear is not divisible by the number of teeth on the blue gear. This is deliberate. If the orange gear had thirty three teeth then every three turns of the blue gear the same teeth would mesh together which could cause excessive wear. By using none divisible numbers the same teeth mesh only every seventeen turns of the blue gear.

“Gears”

Increase/Decrease Intermittent Motion

On the left is a simple pulley. As the rope is pulled down the weight moves up by the same distance.

In the compound pulley on the right the rope is wrapped around two pulleys. As the rope is pulled the weight, this time attached to the lower pulley rather than direct to the rope, moves up slower than the speed that the rope is pulled. Corresponding to this reduction in speed is an increase in the force on the weight.

The amount of increase in the force depends on how many times the rope wraps round the pulleys. By wrapping the rope several times around the pulleys it is easily possible to lift your own weight off the ground!

Reflect Intermittent Motion“Pulley”

Reflect Intermittent Motion

Belt drives are used transfer rotational motion from one place to another.On the left, both pulleys are the same size. Drive can be transfered by friction of the belt on the pulley or, if required, buy using a toothed belt. Chain drives work in a similar way.

By crossing the belt the direction of drive can be changed. On the right two sizes of pulley are used to show how speed of rotation can be changed.

“Belt Drive”

Levers are an essential part of many mechanisms. They can be used to change the amount, the strength and the direction of movement. The position of the force and the load are interchangeable and by moving them to different points on the lever, different effects can be produced. The fixed point of the lever about which it moves is known as the fulcrum. In this example the force and the load move in opposite directions. With the force three times closer to the fulcrum them the load lifted is only one third of the force but it move three times as far.

“Lever”

Reflect Intermittent Motion

First order lever. Like a see-saw or balance, the load and the force are seperated by the fulcrum. As one moves up the orther moves down. The amount and the strength of the movement is proportianal to the distance from the fulcum

“Lever”

Reflect Intermittent Motion

Second order lever. A wheel barrow is a second order lever. Here the load is between the force and the fulcrum. This uses mechanical advantage to ease lifting of a large weight.

“Lever”

Reflect Intermittent Motion

Third order lever.Here the force is between the fulcrum and the load. Mechanical advantage is reduced but the movement at the load point is increased.

“Lever”

Reflect Intermittent Motion

The bell crank is used to convert the direction of reciprocating movement. By varying the angle of the crank piece it can be used to change the angle of movement from 1 degree to 180 degrees.

The bell crank was originally used in large house to operate the servant’s bell, hence the name.

“Jeeves, where’s my tea?!”

“Bell Crank”Rotate intermittent Motion