Reciprocating Motion

1. Motion Reciprocating Motion Reciprocating motion is back and forth motion. In the example to the left the reciprocating motion of the piston is converted to the rotary motion in the crank. Reciprocating motion is measured by its throw (the distance between the two extremes of motion) and by its period (the length of time for each cycle)

2. Reciprocating to Rotary Motion “Piston” This mechanism is used to convert between rotary motion and reciprocating motion, it works either way. Notice how the speed of the piston changes. The piston starts from one end, and increases its speed. It reaches maximum speed in the middle of its travel then gradually slows down until it reaches the end of its travel.

3. Reciprocating to Oscillating Motion “Four Bar Linkages” Linkages are an essential part of many mechanisms. They can be used to change direction, alter speed and change the timing of moving parts.In this example two linked linkages are used to convert the small linear movement of the drive shaft (bottom left) into first a rotational body movement and secondly a fast hammer movement. Compare the speed of the hammer with the speed of the drive shaft!

4. Reciprocating to Oscillating Motion “Four Bar Linkages” The basic 4 bar linkage. All four bars make up a parallelogram. Two, equal length orange shafts and the distance between the joints on the red moving bar and yellow fixed bar being equal. The movement of the top arrange shaft exactly shadows the movement of the lower orange bar.By changing these lengths and the lengths of the other bars different movements can be achieved.

5. Reciprocating to Oscillating Motion “Four Bar Linkages” This time, two different lengths of bar, the two long bars, yellow and red are the same length as before.Look at the tip of the red shaft, notice how it moves smothly until the last second then flips to the right. The same effect is used in the Motley Man to make him look up at the last moment of his bow.

6. Reciprocating to Oscillating Motion “Four Bar Linkages” Quite an extreme arrangement this! With the two long bars crossing over each other. A more extreme 'kick' in the orange bar this time at the end of the green bar's travel. Looks like a likely mechanism for a model!

7. Reciprocating to Intermittent Motion “Ratchet” The ratchet can be used to move a toothed wheel one tooth at a time. The part used to move the ratchet is known as the pawl. The ratchet can be used as a way of gearing down motion. By its nature motion created by a ratchet is intermittent. By using two pawls simultaniously this intermittent effect can be almost, but not quite, removed. Ratchets are also used to ensure that motion only occurs in only one direction, useful for winding gear which must not be allowed to drop. Ratchets are also used in the freewheel mechanism of a bicycle.

8. Increase/Decrease Reciprocating Motion “Lever” 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.

9. Reflect Reciprocating Motion “Pulleys” 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!

10. Rotate Reciprocating Motion “Bell Crank” Reciprocating motion is back and forth motion. In the example to the left the reciprocating motion of the piston is converted to the rotary motion in the crank. Reciprocating motion is measured by its throw (the distance between the two extremes of motion) and by its period (the length of time for each cycle)