outside the robot with LiPo chargers
and use them wisely. Store them
outside your robot when not in use,
as they can ignite when being
charged or when the robot is in a
dormant state.
Model helicopters, quadcopters,
and robots with LiPo batteries have
set many car’s backseats on fire.
That’s the price you pay for otherwise
great batteries.
Ready-built Robot
Bases
Parallax built a large 18" diameter
robot base for their Eddie robot, and
also for their MadeUSA (see Figure
15). This particular photo shows an
added Eddie controller board seen on
the bottom platform. It was a bit
pricey for most builders as it had
expensive-to-make machined wheels
and mounts made in the US-based
Parallax facility, and 10 Ping))) and IR
sensors on the periphery. I've
consulted with Ken Gracey and his
engineers on the design of a low cost
yet high quality large base and they
have come up with a $336 base called
the Arlo Robot. (They are hoping to
drop the price even lower.)
The new base uses the same
gearmotors and 18" platforms, but
uses molded plastic mounts and
wheels as shown in Figure 16.
Adding their HB- 25 fan-cooled motor
controllers, a second platform, IR
and ultrasonic sensors, quadrature
encoders, and even using machined
aluminum wheels and mounts are
available as upgrades or options.
The Wild Thumper robot base
shown in Figure 17 is an ideal
mid-size base at 16. 5” long by 11. 5”
wide at the wheels, and 5” high.
It weighs six pounds and has a
5 kg/11 pound payload capacity. It
features a 2. 5” ground clearance
when lightly loaded.
Several robot suppliers carry this
base and some add their own
drivers. The $350 Parallax version
includes two of the Parallax HB- 25 fan-cooled motor controllers and also a
Propeller project board. The six wheels
are independently spring-loaded to
traverse rough terrain but do have
Ackermann steering.
To drive the robot,
the three right motors
and the three left
motors are driven
differentially by the two
motor controllers. It is
definitely skid steering.
Drawing 6. 6 amps each
at stall, that’s 19. 6
amps for each side.
Internally, there is room
for the two controllers
in one compartment
and a LiPo or NiMH
battery in the other
compartment. You can drive the
wheels at 350 RPM for a 34:1 ratio
gearmotor — that is a fairly high speed
for a robot. It is one great base for
the price.
iRobot came out with the Create
shown in Figure 18 in 2007 as a way
SERVO 12.2013 79
Figure 15. Original Parallax MadeUSA
base with Eddie controller.
Figure 16. New Parallax Arlo robot with
HDPE wheels and mounts.
Figure 17. Wild Thumper six--wheel drive
robot base.
Figure 18. iRobot
Create base.