FIGURE 5. The MadeUSA robot uses custom-made pneumatic wheels.
You can adjust the air pressure for a firm or soft "ride."
FIGURE 7. Carefully align the encoder disc so that
it's between the sides of the slotted optical
switch. Gently push the disc back and forth
along the wheel shaft.
The wheel encoders on the MadeUSA operate a bit
differently than what you might find on most other robots.
The typical encoder arrangement provides velocity control;
in typical use, the microcontroller on your robot monitors
the timing of the encoders from both wheels, and makes
on-the-fly speed corrections to keep both wheels turning at
the same rate.
On the MadeUSA, the wheel encoders are engineered
to provide position control. Rather than simply tell the robot
to go forward, you specify how far to go forward. The
encoders keep track of the distance of both wheels. When
the robot has reached its destination, the motors are
automagically turned off.
The wheel encoders also provide a means to control
not only the speed of travel, but also acceleration and
deceleration. Suddenly starting and stopping a robot as
large and heavy as MadeUSA can put a strain on the
motors and other mechanics. In operation, the wheel
encoders command the HB- 25 drivers to ramp up to speed
for regular travel, then slow back down again as the desired
position is reached.
Building the MadeUSA Kit
MadeUSA comes as a kit, and
building it requires a solid couple of
hours. Before starting, review the
assembly documentation that comes
with MadeUSA to determine if you
have the proper tools. At a minimum,
you’ll need a basic assortment of
standard hex wrenches, and a #1
Phillips screwdriver.
After familiarizing yourself with all
the components, assemble the wheels
first — they have the most parts. The
wheels (Figure 5) are constructed with
a pneumatic inner tube, rubber tire,
custom machined aluminum hub,
aluminum rim, and an axle. When
FIGURE 6. The completed motor
assembly, showing the heavy-duty
pillow block and assembled wheel.
40 SERVO 01.2012
