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8. INFORMATION ABOUT GEARS
The mechanics of the SKY WALKER ROBOT consists of two parts. The first part is
the gear box, which takes care that the power from the motor shaft is converted to the
crank. The second part is to convert the rotation of the crank into a movement of the
feet.
The transmission of power
Gears, transmission belts, shaft, crank, chains: They all can transmit power. In the
Sky Walker, four gears transfer the motor power into the crank. Such a transmission
is called a gear box. The Sky Walker motor rotates very fast with only a little torque.
However, for the crank we need low rotation speed and high torque. The power is
transmitted by the teeth of the gears. At the same time, three conversions take place:
a. Change in rotating direction
b. Change in rotating speed
c. Change in torque
a. Change in rotating direction
When two gears are connected, there will be a change in rotation
direction. One gear will rotate clockwise, the other gear will rotate
counterclockwise.
b. Change in rotating speed
The change in rotating speed depends on the relation of the teeth in the gear. As an
example we describe a gear with 10 teeth and a gear with 40 teeth.
When the first gear (10 teeth) makes a full rotation, the second
gear 40 (teeth) only makes a quarter of a rotation. So before the
second gear makes a full rotation, the first gear already makes four
rotations. You may understand that this effect also changes the
rotating speed.
c. Change in torque
The torque can be seen as a lever construction with a
fulcrum. Imagine a person who lifts a stone with a lever.
Right rotation
Left rotation
10
Teeth
40
Teeth
Fulcrum
B
The person who lifts the lever
must use more force when the
distance A gets shorter or when
the distance B gets longer.
Motor rotation
Gear ratio =
Number of
last gear rotation
A
B
Lever
Fulcrum
Fulcrum
A