■ PHOTO 4. Robot parts
prior to assembly.
■ PHOTO 3. Laser-cut robot platform.
(at least I do). This will allow us to pull
the two PWM values we need from
the board to feed the motor driver.
Next, we solder two more wires
to pins 17 and 19 of the header and
feed those, as well, to the motor
■ You can purchase the SARD board
directly from Zigbee at this link:
■ You can download the free Code
Warrior development tool at this link:
■ You can get online help on
Freescale Zigbee at the following
forum link: www.freegeeks.net/
■ You can also purchase Zigbee
modules at the Maxstream website.
■ You can purchase the Tamiya parts
and more from Zagros Robotics.
■ You can have the robot platform
cut at Rutherford Robotics:
■ You can purchase the LiPol
driver (see Photo 2).
In the UART code, we had to
initialize ports PTC0 and PTC1 to output and then later, when a PWM value
and direction bit was received, we set
the ports accordingly — 1 for forward
and 0 for reverse. Similarly, we had to
initialize the PWM ports and then output the received PWM, where 0 was
stop and 255 was full on in whatever
direction the direction bit specified.
All the references to LED3 and LED4
were commented out of the code so
as not to interfere with the PWM.
All we need now is something to
run all of this on ...
I am a big fan of circular bots with
two wheel differential drive, the
reason being, when they are stuck in a
corner, the can rotate in place and
simply drive away. For a surface to
mount motors and the electronics to, I
quickly drew up a simple drawing in a
CAD program and
had my buddy Jerry
ics.com cut it on his
laser printer out of
“white board” material (see Photo 3).
For the differential drive, I chose
the Tamiya Double
Gearbox and Tamiya
Sport wheels and,
after that, all that was
left was something to
support the front and back. A caster
wheel similar to a furniture caster
would work fine (if you could get one
small enough), however, Tamiya
makes a ball caster which is just the
perfect size and works great. On short
notice, I was able to obtain all the
Tamiya parts and the motor driver
directly from the Zagros Robotics
For a power supply, I am a fan of
Lithium Polymer (LiPol) for a number
of reasons. They are compact, small,
and square; they have decent mAh
values — typically 1,200 or 1,500 —
and they can deliver high multiples of
“C” amps (i.e., about 10+ times the
cell’s capacity). This means you could
deliver 10+ amps in a pinch. A two-battery cell LiPol in series delivers
from 8. 4 volts on full charge, down to
six volts when discharging and, since
the motor driver we chose requires
five volts for its logic, I used a 7805 to
reduce the LiPol output to five volts.
The Sard card will accept from
■ PHOTO 5. The completed robot
— top view!
■ PHOTO 6. Here’s a side view of the