Page 338 - Lego Mindstorms

Robot 10 • RIS Turtle

Turtle Step 35

Add the axle and gears for the gear shifter. It is interesting to
note the unique property of the worm gear that makes this
assembly possible: The axle can slide freely through the worm
gear while still able to turn it. The way the gear shifter works
is by sliding the two crown gears back and forth along the
axle. The direction the axle turns depends on which of the
two crown gears is in mesh with the gear that drives them.

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