enough for the basic experiments we’ll be doing in this
series of articles. Don’t let the small size of the breadboard
limit you. The ArdBot is large enough for bigger
breadboards, even multiple boards, should you need them.
You might want to start with the mini breadboard, then as
you use the ArdBot for further experiments you can add
more prototyping space.
About the Servo Drive
The ArdBot uses differential steering where the base is
propelled by two motors and wheels on opposite sides. To
keep costs down and minimize construction complexity, the
robot uses a pair of skids placed in the front and rear to
provide balance. With this arrangement, the ArdBot is able
to move forward and back, turn left and right, and spin in
place. The skids are smooth and polished metal, so they
present little drag on whatever surface the robot is rolling
over. Even so, the ArdBot is best suited for travel on hard
surfaces or carpet with a short nap.
The two drive motors run off their own battery supply
which is a set of four AA rechargeable or non-rechargeable
cells. The motors are standard size radio control airplane
servos that have been modified for continuous rotation.
The ArdBot reference design uses servos that come
from the factory already modified so you don’t have to
hack them. I used a pair of GWS S- 35 servos, but there are
others available (see Sources) for under $15 each. I won’t
provide instructions here on how to modify a servo for
continuous rotation. That subject has been tackled in past
issues of SERVO and Nuts & Volts, so I’ll leave it at that.
Making the ArdBot Base
The ArdBot is constructed with four body pieces held
together with hardware fasteners. Table 1 provides a full
list of mechanical parts. Tables 2 through 5 specify the
other components to complete the ArdBot.
All body pieces assume 1/4” thick material. For your
reference, Figure 1 shows a completed ArdBot, ready to be
programmed and played with. The body pieces include:
• Bottom deck measuring 7” diameter with cutouts for
the wheels (see Figure 2). The deck includes a
number of holes, of which only six are required. Any
other holes are up to you. I’ve included several
additional holes at the front and back of the deck for
mounting bumper switches and other sensors. The
wheel cutouts measure 2-5/8” x 7-5/8”; sized for
commonly available 2-1/2” or 2-5/8” diameter robotic
wheels for R/C servo motors.
• Top deck measuring 7” x 5” (see Figure 3). Only four
of its holes are critical; these mate with matching
holes in the bottom deck using a set of four
standoffs. A 1/2” diameter hole in the center (or
thereabouts) provides a throughway for wires from
the bottom deck. The other holes as shown are
optional, and are for attaching sensors and other
Table 1. Mechanical Parts.
1 7” diameter bottom deck with wheel well cutouts for the drive wheels.
1 7” × 5” top deck.
2 Servo mounts.
90° plastic L brackets for attaching the servo
mounts to the bottom deck. These brackets
measure 3/4” × 3/4” with hole centers at 3/8”, and
are made to work with the two servo mounts.
16 4-40 x 1/2” machine screws and nuts for attaching the servos and servo mounts to the bottom deck.
Deck risers consisting of: ( 4) 1-3/4” aluminum
(or plastic) risers with 4-40 threads; ( 4) 4-40 × 1/2”
pan head machine screws; and ( 4) 4-40 × 1/2”
flat head machine screws.
2 Skids consisting of: ( 2) 8-32 × 3/4” machine screws; ( 2) 8-32 hex nuts; and ( 2) 8-32 acorn (cap) nuts.
Sets of mounting hardware for Arduino Uno,
consisting of ( 3) 4-40 × 1/2” machine screws;
( 3) 4-40 nuts; and ( 3) plastic washers.
For your convenience, all mechanical pieces — including
precut decks and servo mounts — at are available through
Budget Robotics. See the Sources box for details.
Table 2. Motors and Wheels.
Standard size R/C servo motors, modified
for continuous rotation.
2-1/2” or 2-5/8 diameter wheels with hubs
to attach to the servo motors.
FIGURE 1. The completed ArdBot with Arduino microcontroller
board, solderless breadboard, servos, wheels, and all body parts.
SERVO 12.2010 53