Budget Robotics TankBot Servo User manual

Budget Robotics - TankBot Servo Page 1
Copyright (c) 2002-2006, Budget Robotics
Budget Robotics
TankBot Servo
Assembly Instructions
The Budget Robotics TankBot Servo kit is a low-cost servo-driven tracked vehicle designed as a flexible
base which you can use to construct a fully-featured treaded robot.
The TankBot Servo uses two pre-modified R/C servo motors (44 oz-in torque at 6 volts), and a Tamiya
Track and Wheel Set (70100). The Track and Wheel Set contains plastic drive sprockets and idler
wheels, as well as lengths of rubber tracks that are linked together to make treads. Assembly of the
TankBot Servo is easy, and takes less than 20 minutes.
Two decks, or "levels," are provided, for mounting the batteries, sensors, microcontroller, and other
components. An optional third level is available. The finished robot measures approximately 6.75" in
length, 4.75" wide, and 3.5" high. Weight without batteries is approximately 13 oz.
Note that the TankBot Servo kit lacks circuitry for controlling the servo motors. Any of a number of
microcontrollers can be used for this purpose, and most are sized to fit the TankBot. As an example, the
OOPic R is one of many ready-to-go microcontrollers that can be readily used with the TankBot Servo.

Budget Robotics - TankBot Servo Page 2
Copyright (c) 2002-2006, Budget Robotics
Parts List
The TankBot Servo kit contains the following parts:
Quantity Description
1 Base measuring 5 3/8" x 2 1/2"
1 Second deck measuring 4 5/8" by 2 7/8". The base and second deck are separated by risers
2 Left and right track mounting rails
1 Track rail top support
1 Tamiya Track and Wheel Set (70100); track sprocket attached to a servo disc
2 R/C servo motors
8 4-40 x 1" machine screws (used as wheel axles)
8 4-40 nylon locking nuts
8 Small profile #4 washers (brass color)
16 #4 washers
8 4-40 x 1/2" machine screws and nuts
4 Risers consisting of: (4) 6-32 x 1 1/2" machine screws, (8) 6-32 hex nuts, (4) sleeves
6 #6 x 3/4" self-tapping screws

Budget Robotics - TankBot Servo Page 3
Copyright (c) 2002-2006, Budget Robotics
Assembly Steps
Step 1
Identify the "right" and "left"
track rails. The "left rail" is the
rail on the left, as viewed from
the rear of the TankBot. Its three
base mounting holes are
countersunk on the left side.
The "right rail" is the rail on the
right, as viewed from the rear of
the TankBot. Likewise, its three
base mounting holes are
countersunk on the right side.
Orient one servo in the servo
mounting pocket of the left rail,
as shown.

Budget Robotics - TankBot Servo Page 4
Copyright (c) 2002-2006, Budget Robotics
Step 2
Using 4-40 x 1/2" machine
screws, nuts, and #4 washers,
secure the servo to the top
mounting slot of the left rail.
The nuts face to the outside of
the rail.
Be sure to place the washers as
shown in the inset figure. One
washer should be flush against
the nut, the other flush against
the head of the screw.
Repeat for the bottom of the
servo. Observe the fasteners are
attached at opposite corners of
the servo.
Note: Four sets of fasteners are
provided for each servo, but only
two are needed. Hand-tighten
only at this point.

Budget Robotics - TankBot Servo Page 5
Copyright (c) 2002-2006, Budget Robotics
Step 3
Secure three small rollers from
the Tamiya Track and Wheel set
to the left rail using 4-40 x 1"
machine screws, washers, and
locking nuts (see the figure inset
for fastener assembly).
Note that the washers, which are
brass color, are undersized, and
may need to be threaded onto the
machine screws.
Hand tighten the locking nuts
only at this point.
Step 4
Secure one large roller from the
Tamiya Track and Wheel set to
the left rail using a 4-40 x 1"
machine screw, washers, and
locking nut (see the figure inset
in Step 3 for fastener assembly).
As with the small rollers in Step
3, only hand tighten the locking
nut.

Budget Robotics - TankBot Servo Page 6
Copyright (c) 2002-2006, Budget Robotics
Step 5
Using a #0 Phillips screwdriver,
along with a box wrench or pair
of pliers, tighten the locking nut
on each of the four rollers.
Best results can be obtained with
the following:
1. Tighten the nut so that the
roller no longer freely
rotates.
2. Untighten by 1/8 of a turn
until the roller spins
without binding. Do not
untighten to the point
where the roller becomes
wobbly.

Budget Robotics - TankBot Servo Page 7
Copyright (c) 2002-2006, Budget Robotics
Step 6
Assemble the treads from the
Track and Wheel Set using the
following lengths for each tread
(for an overall length of
approximately 14 1/2"):
1 7 1/2"
1 2"
2 2 1/2"
Temporarily mount one
completed tread to the left rail as
follows:
1. Push the servo as far toward
the front of its mounting slots
as possible.
2. Loop the tread over the four
idler wheels.
3. Wrap the tread around the
teeth of the drive sprocket,
and carefully push the
sprocket onto the servo
motor shaft.
4. Pull the servo back in its
mounting slots to exert
medium tension on the tread.
The tread should be springy,
but not overly tight.
Note: Do not overstretch the
tread or it may become unlinked.
If desired, at this time you may
attach the other two sets of
machine screws, nuts, and
washers to the servo motor.
For ease of construction,
remove the drive sprocket and
track when the above steps are
done. The servos do not need to
be loosened. Simply remove the
sprocket from the servo motor
shaft.

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Copyright (c) 2002-2006, Budget Robotics
Step 7
Repeat steps 1 through 6 for the
right rail.
When completed, you should
have two rail sub-assemblies, as
shown here.
Step 8
Orient the base so that the two
riser mounting holes furthest
from the edge are located to the
rear of the TankBot (by the
servo motors).
Using two #6 x 3/4" self-tapping
screws, attach the left rail as
shown.
Do not over-tighten the screws,
or the plastic may become
deformed.

Budget Robotics - TankBot Servo Page 9
Copyright (c) 2002-2006, Budget Robotics
Step 9
Repeat step 8 for the right rail.
Step 10
Using two #6 x 3/4" self-tapping
screws, attach the track rail top
support, as shown.
Do not over-tighten the screws,
or the plastic may become
deformed.

Budget Robotics - TankBot Servo Page 10
Copyright (c) 2002-2006, Budget Robotics
Step 11
Assemble the risers to the base
as follows:
1. Push each of the 6-32 x 1
1/2" machine screws into
the four holes in the base.
The screws are inserted
from the bottom.
2. Slip a plastic sleeve over
each of the screws.
3. For each riser, thread a 6-
32 hex nut until the sleeve
is slightly compressed.
Step 12
Mount the top deck by aligning
its four holes with the riser.
Secure the top deck to the risers
with four 6-32 hex nuts.
Your TankBot should look like
the model on the right (drive
sprocket shown for placement).
(Note: The sprocket and rollers
are not inline. This is intentional.
The center-line of the sprocket is
inset approximately 5/64"-1/8"
from the center-line of the
rollers.)

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Copyright (c) 2002-2006, Budget Robotics
Step 13
Replace the tread and drive
sprocket as follows for both the
left and right side:
1. Loop the tread over the
four idler wheels.
2. Wrap the tread around the
teeth of the drive sprocket.
3. Carefully push the sprocket
onto the servo motor shaft.
4. Secure the sprocket to the
servo motor shaft with the
supplied shaft screw.
Notes
1. An optional third level is available if you need more space for additional electronics (sensors,
video camera, etc.). The third level measures 4 5/8" square. The extra level is available from
Budget Robotics, at the address below.
2. The TankBot is naturally heavy on the motor-end. For best weight distribution, mount the
batteries toward the front of the base.
3. To avoid "skipping" in turns, reverse the motor on the side you wish to turn to (that is, to turn
right, reverse the right motor while keeping the left motor going forward).
4. If the track pops off the idler wheels or drive sprocket, check the links between each length of
track. Adjust the tread tension as necessary.
5. As necessary, the track segments can be held in place by applying a small amount of low-
temperature hot glue to the segment joints. While the glue cools, press it into place by putting the
track upside down on a flat surface, and "rolling out" the glue with the drive sprocket. This
ensures that the glue doesn't fill the sprocket holes in the track.
Servo Centering Adjustment
The TankBot Servo 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 each 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.

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Copyright (c) 2002-2006, Budget Robotics
Should you wish to adjust the physical center of the servo you may do so by following these steps:
1. Remove the drive sprocket from the servo.
2. Remove the servo from the track mounting rail.
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.
Reattach the servo to the track mounting rail, and the sprocket to the servo.
The TankBot Servo is available from:
Budget Robotics
PO Box 5821
Oceanside, CA 92056
http://www.budgetrobotics.com/
[e-mail]
120407