Budget Robotics Octabot Assembly Instructions Manual

Budget Robotics

Octabot

Assembly Instructions

The Budget Robotics Octabot kit is a low-cost 7" diameter servo-driven robot base, ready for expansion.
Assembly is simple, and takes less than 15 minutes.

The Octabot comes with two "decks" for mounting the servo motors, batteries, sensors, microcontroller,
and other components. Additional decks can be added if desired. We recommend no more than three
decks total, to reduce the possibility of the robot tipping over.

The Octabot uses the popular "differential steering" motor arrangement, where the robot is propelled by
two motors and wheels on opposite sides of the base. A caster, placed at the rear of the Octabot,
provides balance. With this arrangement, the Octabot is able to move forward and back, turn left and
right, and spin about the axis of the wheels.

The two drive motors are standard R/C airplane servos. Normally, such servos are limited to 180°
rotation only, but the motors included with the Octabot have been modified to permit continuous
rotation. As with all R/C servos, the Octabot motors must be driven using the appropriate control circuit.
This control circuit is not included with the basic Octabot kit.

If you need a control circuit, the OOPic R, from Savage Innovations, (http://www.oopic.com/) is a good
all-purpose solution. The board has connections for attaching up to 16 R/C servos.

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Riser mounting

Servo

mounting

Caster

The Octabot kit contains the following parts:

Quantity

Description

1 7" diameter base (bottom deck). The base has "wheel well" cutouts for the drive wheels. The

base is pre-drilled for the servo motor mounting brackets and caster.

1 7" diameter 2nd deck. The 2nd deck is attached to the base using risers. Holes in this deck

match mounting holes in the base.
2 Pre-modified R/C servo motors.
2 2 1/2" diameter wheels, with hubs to attach to the servo motors.
2 Servo mounts, engineered to fit most any standard-size servo.
4 90° corner brackets, for attaching the servo mounts to the base.
16 4-40 x 1/2" machine screws and nuts.
4 Risers consisting of: 6-32 x 2" machine screws, 6-32 hex nuts, and sleeves.
1 Swivel caster.
2 Caster hardware consisting of: (2) 6-32 x 1/2" machine screws and (2) 6-32 hex nuts.

Assembly Steps

Step 0

Orient the base (bottom deck) as
shown. This will be the
underside of the base.

Note the servo mounting holes
on the left and right side, as well
as the caster mounting holes.

Four additional small holes are
pre-drilled for the risers. They
are located on the front and rear
(the rear is considered the end
with the caster), and the left and
right sides.

The remaining larger holes are
for feeding through wires for
servos, sensors, etc.

holes

holes (1 of 4)

mounting
holes

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Copyright (c) 2002-2006, Budget Robotics

Step 1

Viewed from

Mount the left servo corner
brackets over the servo
mounting holes as shown. Use 4­40 x 1/2" screws and nuts to
fasten the brackets in place.

Repeat the same for the right
servo.

The screws should be pushed
through from the bottom of the
base. The nut is fastened on the
top of the base.

Finger-tighten only at this point.

Bracket

bottom

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Copyright (c) 2002-2006, Budget Robotics

Step 2

Mount one of the servos into a
servo mounting bracket by
sliding it back-end first through
the bracket.

The fit may be tight, depending
on the make and model of the
servo. Do not force the servo
into the bracket, or the bracket
may be damaged.

If you are using alternative
servos than those that come in
the Octabot kit, you may need to
lightly file the inside pocket of
the servo mounting bracket to
enlarge it to accommodate your
servo. Don't make the pocket any
larger than it needs to be.

Secure the servo to the mount
with two 4-40 x 1/2" screws and
hex nuts. (There is no need to
use fasteners on all four corners
of the servo; two screws are
sufficient.)

Repeat for the opposite servo
and mounting bracket. Be sure to

mount the servo in mirror-image
to the one shown! Refer to Step

8 to view how the servos are
installed.

4-40 x 1/2”

Servo

Servo mount

bracket

4-40 nut

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Copyright (c) 2002-2006, Budget Robotics

Step 3

Attach the left servo and servo
mount to the base using two 4­40 x 1/2" screws and nuts. The
nuts should be secured to the
side of the mount facing the
wheel well cutout.

Note that when properly
attached, the servo shaft will be
centered in the wheel well
cutout.

Repeat the same procedure for
the right servo and servo mount.

After the servo mounts have
been attached, align the mounts
so they are parallel with the
wheel well cutout, and tighten
all screws.

Step 4

Attach the caster using two 6-32
x 1/2" machine screws and nuts.

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Copyright (c) 2002-2006, Budget Robotics

Step 5

6-32 x 2" screw

Assemble and install the four
risers as follows:

1. Thread each of the 6-32 x
2" machine screws into the
four holes designated for
the risers. The screws are
inserted from the bottom.

2. Slip a plastic sleeve over
each of the screws.

3. For each riser, thread a 6­32 hex nut until the sleeve
is slightly compressed.

Step 6

Mount the wheel to each servo.
The wheel is secured with a
small self-tapping screw.

Note that the servo shaft is
splined, and this spline matches
the wheel hub. Be sure to press
the wheel onto the shaft firmly
while tightening the screw.

Do not over-tighten the wheel
mounting screw, or it may
break off!

Nut

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Step 7

Attach the 2nd deck by locating
the matching four holes to the
risers.

Secure the top deck by threading
four 6-32 "high profile" hex nuts
onto each riser.

These "high profile" nuts act as
couplers in case you wish to add
a third deck to the Octabot.

Step 8

The based is drilled with several
large holes for wire "feed
through," and can be used as
shown.

You may drill additional holes
as needed. A standard wood bit
may be used to drill holes.

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Servo Centering Adjustment

The Octabot uses standard R/C model airplane servo motors that have been modified to allow for
continuous rotation. This modification entails removing a "stop" on the bottom of the drive gear, and
disengaging the drive gear from the feedback potentiometer inside the servo.

Before the servo was shipped to you, the potentiometer was positioned in its physical center position,
but was not cemented in place. This allows you to make fine-tuning adjustments to the servo center to
best suit the control circuitry you are using.

Ordinarily, software running on your servo control circuit or microcontroller is used to set the "center"
of the servo. This signal is nominally a repeating pulse of 1.5 milliseconds in duration. When centered,
the servo stops all motion. Applying a pulse greater than 1.5 milliseconds causes the servo to rotate in
one direction; a pulse of less than 1.5 milliseconds causes the servo to rotate in the other direction. Note
this pulse is repeated 20-50 times each second.

Should you wish to adjust the physical center of the servo you may do so by following these steps:

1. Remove the wheel from the servo.

2. Remove the servo from the servo mount.

3. Remove the four casing screws on the servo.

4. Place the servo upright (base down) on the table, and very carefully remove the top casing.
Apply gentle finger pressure on the output shaft to prevent the output gear from being pulled out
as you remove the casing.

5. Remove the center gear, but keep the metal shaft in place.

6. Remove the output gear. (Minimize handling of the gears so that you don't accidentally "soak
up" too much of the white lubricating grease into your fingers. If you think the gears have
become insufficiently lubricated, you may apply a small amount of synthetic grease -- available
at most electronics stores -- to replenish.)

7. Adjust the feedback potentiometer as required. If needed, you may apply a very small amount of
Super Glue (or equivalent) to the potentiometer shaft to lock it in place.

8. When done, replace the output and center gear. Replace the top casing and four casing screws of
the servo.

9. Reattach the servo to the base, and the wheel to the servo.

The Octabot is from:

Budget Robotics
PO Box 5821
Oceanside, CA 92056
http://www.budgetrobotics.com/
[e-mail]

112303

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Copyright (c) 2002-2006, Budget Robotics

Octabot II

Addendum

Except as noted below, the Octabot II kit contains the same parts as the original Octabot kit.
Construction steps are therefore similar as well.

Quantity

Description

8 Aluminum risers, with (16) machine screws. (Replaces 6-32 hardware risers

of original Octabot.)

1 Extra third deck.

1. Follow construction steps 0-4 in Octabot assembly instructions.

2. For steps 5 and 7, use (4) each aluminum risers and (8) each machine screws to secure second
deck. The second deck aligns with the riser holes in the bottom deck one way only.

An optional third deck is included with the Octabot II kit. It is attached to the second deck using the four
alternate holes.

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Copyright (c) 2002-2006, Budget Robotics