Budget Robotics - TankBot Servo
Page 11
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.