more, but can make the programming slightly easier for
people since the pulse width you send to them means the
same for forward and reverse on both servos. Otherwise,
the pulse widths would mean the opposite from side to
side if one motor isn’t reversed.
Powering the MiniBot
I wanted to make sure there was plenty of power
available to keep the MiniBot rolling for a long time. A
good choice seemed to be a 7.2V 4,200 mAh NiMH flat
battery pack from All-Battery. This battery pack was made
from a set of six Sub-C cells. It is mounted vertically inside
the robot, attached to the back of the can with two
squares of double-sided tape. Two holes are drilled through
the back on each side of the pack near the middle, and a
cable tie is installed around the battery and through the
To make sure the battery pack wasn’t sitting directly on
top of the screw holding the glide on the base, I installed a
pair of stick-on rubber feet to support the battery and
provide clearance. With the extra weight toward the back,
the robot favors the rear slider so it normally ends up
touching the ground when moving.
A power switch and voltmeter were added to wrap up
the power section. The power switch is just a mini toggle
switch located on the back of the robot about 1.25” from
the top edge of the body, centered over the battery. It
breaks the circuit on the positive lead coming from the
battery pack. In order to keep tabs on the battery voltage, I
picked up a small DC 3.3V-17V blue LED voltage monitor. It
has three seven-segment displays.
There are a couple different variations on eBay that I
have seen for sale. Make sure to look for the two-wire
versions since they can be powered directly from the
battery you want to monitor. Avoid the three-wire versions
since you would have to provide an additional power source
to power the meter itself.
Position of the drive wheels and glides on base.
Main drive servos and wheels.
Sliders used at front and rear of base.
Mounting of the servos and glides.
SERVO 05.2013 49