your computer (we’ll get to why you might want to do this
in the next installment). By simply disconnecting the
batteries for the motors, your ArdBot II will think it’s driving
around, but, in fact, won’t move.
Another important reason to use separate supplies is
changing out those unrechargeable 1.5 volt AA cells with
rechargeable ones. In the long run, it’ll save you a ton of
money — robots use up batteries like kids eat candy. The
rechargeables are also better on the environment.
The nominal voltage output of nickel cadmium or
nickel-metal hydride cells is 1.2 volts; four together provide
4. 8 volts. That’s enough to motivate the robot’s two servo
motors, but not enough to power the Arduino’s regulator.
Making Your Own ArdBot II
With the design basics out of the way, let’s turn to
building the ArdBot II. Construction is simple, requiring only
one square foot of material. You need four pieces total: one
for the bottom base, with small cut-outs for the wheels;
one for the top base; and two for the servo mounts.
A cutting and drilling diagram for the main top and
bottom decks is provided in Figure 3; Figure 4 shows a
cutting and drilling guide for the servo mounts.
You can use 1/4” plywood or my preference: 6 mm
expanded rigid PVC plastic. The plastic is lighter weight, and
if purchased locally from a plastics distributor, is often
cheaper than wood. Either way, plywood and PVC can be
readily cut using ordinary wood tools. I suggest a coping
saw for working by hand, but recommend a motorized
table scroll saw for the fastest and most accurate cutting.
Servos and servo mount hardware
4-40 x 1/2” pan head machine screw
4-40 x 1/2” flat head machine screw
4-40 hex nut
3/4” x 3/4” plastic angle bracket*
Arduino mounting standoff hardware
3/4” to 1” (approx.) length nylon standoffs, 4-40 thread
4-40 x 1/4” pan head nylon machine screw
4-40 x 1/2” flat head machine screw
6-32 cap (acorn) nut
6-32 × 3/4” pan head machine screw
6-32 hex nut
Deck risers (standoffs)
Standoffs with 4-40 or 6-32 threads, at least 2” or longer
4-40 or 6-32 pan head machine screws
* For the 3/4” x 3/4” plastic angle brackets, you can substitute the nearest
smallest metal L brackets available. The plastic brackets weigh a little less.
You can use any type of drill — all holes are 1/8” unless
otherwise indicated. Some hole locations are critical, so
follow the old adage: Measure twice, cut (or drill) once.
When marking off the holes for the Arduino in the top
deck, use your Uno board for the hole locations. I include
all four mounting holes, although on the latest Unos you’re
likely to only use three of them since the one in the upper
left corner is very close to the top row of headers. The hole
is still there in the board in case you want to mount it with
a shield stacked on top.
If you’d prefer not to do the cutting and drilling, see
the Sources box for a kit of parts, including precut body
pieces and assembly hardware.
To complete the ArdBot II, you’ll need the hardware
listed in Table 1 to put all the pieces together. Except for
the skids and riser standoffs, I’ve specified 4-40 size
hardware for everything. While 4-40 machine screws and
nuts are a little harder to find than their more common 6-
32 siblings, their smaller size makes them better candidates
for a small robot. They also weigh less, and the less weight
a robot has, the longer its batteries will last.
If your local home improvement store doesn’t have the
4-40 hardware, you can always get it online; see the
Sources box for a small selection of Web retailers that
carry miniature fasteners.
Tip: When searching the local digs for miniature nuts
and screws, try the smaller hardware stores first. They’re
more likely than the “big box” retailers to have what you’re
In addition to the assembly hardware, at a minimum
you need the additional components in Table 2 to build
your ArdBot II. Some additional parts will be needed to
complete other functionality of the robot. We’ll cover these
2 Standard size servos, continuous rotation, Futaba compatible splined hubs
2 2-1/2” or 2-5/8” wheels with Futaba compatible hubs
1 Arduino Uno microcontroller board
1 Mini solderless breadboard (170 tie points, double-sided foam tape on back)
1 4 x AA battery holder
4 AA batteries (alkaline or rechargeable)
1 Nine volt battery snap and wires (lead length should be at least 6”)
1 Nine volt battery
1 2.1 mm barrel solderable connector
1 Miniature piezo speaker
2 Snap action leaf switches (standard size)
1 12” length three-wire (signal, power, ground) extension
Misc Pre-made female-female jumper wires* (some will be cut to length)
Misc Set of 10 or more double-length break-away header pins
Misc 12” length of 0.25” OD (outside diameter) aquarium tubing**
Pre-made female-female jumper wires and double-length break-away
headers are available from Pololu. I recommend the 50 pack of 3” length
female-female jumper wires (rainbow assortment), part number 1706. This is far
more than you’ll use for the ArdBot II, but the extra will always come in handy.
This tubing is used for extending the contact area of the leaf switches.
We’ll get to this aspect in an upcoming installment of the series.
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