Page 329 - Lego Mindstorms

Robot 10 • RIS Turtle

Turtle Step 22

Insert a #2 axle into
the cam. Note that only
the outer cam will hold it.

Bricks & Chips…

Unorthodox Assemblies
The reason for this strange assembly is that a crank with a total stroke of 1 unit
is required for the gear shifter. This is because it will eventually be used to shift
between two gears that are spaced one unit apart on a shaft. To provide a total
stroke of 1 unit, the axle must be connected one half-unit from the drive shaft.
There is a special TECHNIC crank piece that is made for a half-unit offset, but
the RIS doesn’t include any. But two cams can be used together to provide the
correct spacing. This is because the cams have several mounting holes at dif-
ferent spacing, and three of these holes just happen to be one half-unit apart.
Two cams must be used because the width of an axle is greater than one half-
unit, so the axles can’t be placed side by side, but must be installed one in
front of the other. This is one example of many situations where a construction
requires a half unit spacing. The TECHNIC cam is one part that can be used to
provide a half unit offset, while other parts include the 1x1 beam with a hole,
or 1x2 beam with two holes, or the plate with one bump in the center.

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