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|THE SNAIL / DROP CAM
|V. Ryan © 2006 - 2020
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Eccentric, heart shaped and pear shaped cams
generally allow for a slow rise and fall of the follower. However, a
snail drop cam is used where the drop or fall of the follower must be
The diagrams below shows the rotation of the snail/drop cam. When rotating for one complete revolution the follower stays level for approximately the first 120 degrees (diagrams 1 to 4). The follower then rises slowly (diagrams 5 to 6) and then suddenly drops when it reaches and passes the peak (diagram 7).
|WHAT HAPPENS WHEN A DROP CAM ROTATES IN THE WRONG DIRECTION?
|Direction of rotation of the cam profile is very important, especially when a drop cam profile is being used.
The example opposite shows what happens when this profile rotates in a clockwise direction. The roller follower, ‘jams’ the mechanism. This will usually prevent the profile rotating any further and can even break of damage the mechanism.
The mechanical toy seen below has a snail/drop cam as
its main part. The follower is connected to the characters arm by a wire
link. As the cam rotates, the follower rises and the wire link lifts the
characters arm. This gives the appearance of the character lifting a
fork full of food towards his mouth.
|Another example of a drop cam is seen below. As the cam profile rotates the foot of the model rises slowly and then suddenly drops.
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