Making Robots With The Arduino part 2.pdf

worldmags

Making Robots

With The

A RDUINO

Part 2

By Gordon McComb

The ArdBot is a low-cost, 7” diameter servo-driven robot base, ready for

expansion. It’s called ArdBot because it’s based on the popular and

inexpensive Arduino microcontroller board. The ArdBot costs under $80 to

build; even less if you already have some of the components, like the

breadboard, jumper wires, and battery holder.

its central Arduino brain. This month, we’ll continue

the discussion with full construction plans for the

ArdBot. I built the reference design using 1/4”

expanded PVC plastic, but you can use wood, acrylic, foam

board, picture frame mat, or most anything else that is rigid

enough for the components.

is the practical minimum and 3” the maximum.

While it’s a bit more challenging to cut circles to make

a robot base, it’s the best overall shape for navigating tight

places like mazes or the corner of a living room. The

concept of the ArdBot is flexibility, however. There’s no

reason your version must be circular. You can make a

square bot if you’d like, or cut off the corners of the square

to make an octagon.

If you don’t want to construct the mechanical pieces of

the ArdBot at all, you can get them precut with all the

hardware; see the SOURCES box. ArdBot is designed for

expandability. If the twin decks do not provide enough

space for all your experiments, you can add more decks. I

don’t recommend any more than three decks total, as any

more may pose a weight problem for the drive system.

The brain of the ArdBot is an Arduino Uno — the latest

of the all-in-one core designs of the Arduino. If you already

own an earlier version of the board — a Diecimila or

Duemilanove — those will work, too. The only requirement

is that you have version 0017 or later of the Arduino

programming environment. The ArdBot project was created

and tested using version 0019 — the latest as of this

writing. Complementing the Arduino microcontroller board

is a mini solderless breadboard. It has 170 tie points —

ArdBot Basic Design

The ArdBot uses two “decks” for mounting a pair of

servo motors, batteries, microcontroller, small prototyping

board, and other components you’d like to experiment

with. The bottom deck is basically a 7” diameter circle with

cutouts for the wheels. The top deck is the same 7”

diameter circle with the side lobes cut off.

The decks are separated by a set of four 1-3/4” long

standoffs. The actual length of the standoffs is not really

important. You can make them shorter or longer — 1-1/2”

In preparing Part 1 of this series, I made a last-minute

change to include the new Ardunio board that's just been

released. Only I got the name wrong — in several places in

the article, I referred to the new board as the Duo. The

correct name for the board is the Uno.

52 SERVO 12.2010

worldmags

I n the last installment, we introduced the ArdBot and

worldmags

www.servomagazine.com/index.php?/magazine/article/december2010_McComb

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.

optional, and are for attaching sensors and other

accessories.

• Pair of servo mounts (see Figure 4 ) for attaching the

servos to the bottom deck. You can make these

Table 1. Mechanical Parts.

About the Servo Drive

Qty

Description

7” diameter bottom deck with wheel well cutouts

for the drive wheels.

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.

7” × 5” top deck.

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.

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.

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.

Making the ArdBot Base

Qty

Description

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:

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.

• 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

FIGURE 1. The completed ArdBot with Arduino microcontroller

board, solderless breadboard, servos, wheels, and all body parts.

SERVO 12.2010 53

worldmags

worldmags

FIGURE 2. Layout pattern for cutting and drilling the bottom

deck of the ArdBot. The only truly critical dimensions are the

cutouts for the wheels and the placement of the two sets of holes

immediately beside the wheel cutouts. These holes are for the

servo mounts. See Figure 5 for a description of all holes.

FIGURE 3.

Layout

pattern for

cutting and

drilling the

top deck of

the ArdBot.

Critical holes

are the four

small ones

nearest the

center. These

must match

the four

servo

mounting

holes in the

bottom

deck.

yourself or, if you choose, purchase them separately.

If you make the mounts, be aware that sizing is

critical. The two holes on either side of the mount

must be spaced 3” apart to accommodate the same

hole spacing in the bottom deck.

circles when using these materials. If you don’t own a

circular jig yourself, see if the local picture frame store will

make the cuts for you. When using picture mat material,

cut two of everything, and double-up the pieces for extra

stiffness. Except for the large center hole in the top deck,

all holes are drilled with a 9/64” bit.

The base parts may be cut from stock measuring 12”

x 12” which is a common size for expanded PVC or other

plastic purchased through mail order. A motorized scroll

saw is the perfect tool for cutting out the ArdBot base

components, but if you don’t have one handy, a coping

saw also works. Use a wood blade; it’ll work whether

you’re making the base with aircraft-grade plywood

(available at the hobby store), PVC, or other plastic.

If using foam board or picture mat, you can cut the

pieces using a sharp hobby knife or mat cutter. The usual

safety precautions apply. A circle cutting jig makes perfect

Assembling the ArdBot

With the body pieces constructed (or purchased) and

all other parts in hand, you’re ready to build your ArdBot.

Here’s how.

Step 0

Before assembly, you may want to use 150 grit

sandpaper to smooth the edges of the base parts. Orient

the bottom deck so that the holes are aligned as shown in

Figure 5 . Note that the holes for each servo are not

symmetrically placed on the deck. This is to accommodate

Table 3. Electronic Parts.

Qty

Description

Table 4. Power.

Qty

Description

Arduino Uno (or compatible) microcontroller

board with USB programming cable.

AA alkaline or nickel metal hybride

rechargable batteries.

Mini solderless breadboard; 170 tie points.

Nine volt battery.

Set of solderless breadboard wire jumpers

(or make your own using 22 gauge solid

conductor wire).

Table 5.

Optional (but nice to have) Parts.

Qty

AA x four battery holder, with female header

connector; see text.

Description

Nine volt battery clip, with 2.1 mm polarized

barrel plug; see text.

Nine volt metal or plastic battery holder.

Hook-and-loop (Velcro) strips for mounting

battery holders and solderless breadboard;

small pieces of double-sided foam tape.

Length of 12 (or more) breakaway 0.100” male

header pins, double-sided (long) pins; see text.

54 SERVO 12.2010

worldmags

worldmags

the offset of the servo drive shaft. While there is

technically no “front” or “rear” of the ArdBot, for

the purposes of assembly, the top of the

illustration in Figure 5 is the front and the

bottom is the rear.

Step 1

Insert a servo into a servo mount by sliding it

back-end first through the mount. The fit may be

tight, depending on the make and model of the

servo. (As necessary, enlarge the rectangle for the

servo using a file or coarse sandpaper.) Do not

force the servo into the mount or the mount may

be damaged.

Secure the servo to the mount with 4-40 x

1/2” screws and hex nuts ( Figure 6 ). You can use

four screws for each servo, or only two. When

using two screws position them on opposite

corners of the servo mounting flange, as shown.

Repeat for the opposite servo and mount. Be sure to

construct the second servo and mount in a mirror image to

the first! Refer to Figure 9 in Step 3 to see how the motors

should be inserted into the mounts. For reference, also see

Figure 12 for an aerial view of the ArdBot and its

completed bottom deck.

FIGURE4. Layout pattern for cutting and drilling the servo mount. You’ll

need two of these. If cutting the inside rectangle proves difficult, you can

instead make the mounts by cutting through at the dotted line.

The mount will be a little more fragile, so handle it carefully.

Use all four screws to secure the servo in the mount, rather than just two.

Insert the machine screws through the L bracket, then

through the servo mount. Secure on the other end with a

nut. Before tightening, be sure the bottom of the L bracket

is flush with the bottom edge of the servo mount.

Step 3

Attach the left mount assembly to the bottom deck

using two 4-40 x 1/2” screws and standoffs. The screws

should come up from the underside of the deck, through

Step 2

Using 4-40 x 1/2” machine screws and nuts, attach

two plastic L brackets to each of the servo mounts ( Figure

7 ). You’ll be make a “left” and a “right” mount assembly.

For the left mount assembly, the motor shaft should

face to the left and toward the “top” of the deck (as

referenced in Figure 5 ). Attach the L brackets to the right

side of the mount. For the right mount assembly, the motor

shaft should face to the right, also toward the top of the

deck. Attach the L brackets to the left side of the mount.

FIGURE6. Servo motor secured into one of the servo mounts.

You need two of these.

FIGURE5. Only four holes are critical for the bottom deck: the two

sets marked Holes for servo mounting, and the front and rear Skid.

The rest are optional for sensors and other

accessories you may want to add later.

SERVO 12.2010 55

worldmags

worldmags

FIGURE7. Attach two L brackets to the servo mount. The L

brackets should be flush with the bottom of the servo mount.

the L bracket, and then into the standoff as shown in

Figure 8 . When orienting the mount assembly, be sure that

the servo shaft is centered in the wheel well cutout. Align

the assembly so they are parallel with the wheel well

cutout, then tighten all the screws. Figure 9 shows how

the completed servo, mount, and standoffs should look.

Repeat the same procedure for the right mount assembly.

FIGURE8. Secure the servo mounts to the bottom deck using

machine screws and threaded standoffs.

The standoffs serve to separate the decks.

1 . Using a screwdriver, thread a machine screw into the

hole at the front and back of the deck (refer to

Figure 5 for the location of these holes). The screw

is inserted from the top of the deck (the side with

the servos). The holes for the skids are undersized

for 8-32 machine screws. When using a soft material

like wood or PVC plastic, the fastener will tap the

hole as you screw it in. Continue threading the screw

into the hole until the head is about 1/4” from the

deck, as indicated in the picture.

Step 4

Attach the front and rear skids as shown in Figure 10 .

Each skid uses an 8-32” machine screw, hex nut, and acorn

(cap) nut.

2 . Put the hex nut onto the screw, followed by the

acorn nut. Tighten the acorn nut against the hex

nut.

Repeat these steps for the other skid. You may adjust

the height of the skid by loosening or tightening the

machine screw in the hole. If you need greater height

adjustment or the hole for the skid is too large to self-tap,

FIGURE9. Here’s how the completed servo mount should look

with standoffs in place.

FIGURE10. ArdBot uses static skids (made with 8-32 metal

fasteners) for front and back balance. You can adjust the height

of each skid to compensate for the diameter of wheels you use.

56 SERVO 12.2010

worldmags

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: