Page 237 - Lego Mindstorms

Robot 8 • The ULK (Useful LEGO Knowledge)

Arm Assembly Step 6

The 16t gear
installed here is an
idler gear. An idler
gear does not affect
the gear ratio of a
gear train. Idler gears
are quite commonly used
in machines to connect distant
axles. They are also used to change
the direction of rotation of the output shaft.

Bricks & Chips…
Gear Trains

A multi-stage gear train amplifies the torque of the LEGO motor to where
it is sufficient to raise ULK’s arm. A worm gear attached to the motor
shaft turns a 24t gear. The 24t gear is attached to the same shaft as a
16t gear. The resulting gear reduction can be calculated by multiplying
together the gear reduction for each stage.

Stage 1 (Worm gear to 24t gear) gear ratio = 24:1
Stage 2 (24t gear to 16t gear) gear ratio = 3:2
Overall Gear ratio = 24 x 3:1 x 2,
which equals 72:2 or 36:1
Wow! That’s a lot of gear reduction.

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