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6 Masterpeice 1 • Stair-Climber

Engineering Trade-Offs

So, by now you may be wondering where is the RCX? Well, as much fun as it would be
to make this model autonomous by adding a few sensors and RCX, it really isn’t prac-
tical.All the extra weight is just too much for the tri-star assemblies of this model to
function properly. When attempting to climb with higher loads, the excessive torque on
the main tri-star axles leads to breaking axles and gears with higher loads.
Beyond this, the main goal of this model was stair climbing and attaching an RCX to the
model would raise the center of gravity (CG) enough to seriously limit vehicle stability,
thus causing the model to flip over backwards when climbing steeper inclines.
However, you could use an RCX as a handheld battery pack if you wanted to, and I
will show you how this is possible toward the end of the chapter. But then again, the
Stair-Climber doesn’t need the processing power, as it uses the differentials to shift
between modes.There is one more reason for just using a battery pack with this partic-
ular model: if you try to turn this model by powering each side separately, you may find
the wheels will slide out of place and jam.
The Wheel Set

The tri-star wheel set has a concentric drive arrangement to provide separate power for
both rolling and stepping modes of operation.The differential housing used without
internal gears provides this concentric drive mechanism and acts to hold the dark gray
16T gears in place.You will need to build four of these.