AmigoBot Mobile Robots
13
Motors and Position Encoders
AmigoBot’s drive system uses high-speed, high-torque, reversible-DC motors. Each front
drive motor includes a high-resolution optical quadrature shaft encoder that provides
9,550 ticks per wheel revolution (approx. 30 ticks per millimeter) for precise position and
speed sensing and advanced dead-reckoning. The tires are 4 inches in diameter and
made of soft, but firm rubber for good traction and low compressibility.
Sonars
The AmigoBot comes standard with a single array of eight sonars. The sonar positions are
fixed: one on each side, four facing forward, and two at the rear, together providing 360
degrees of sensing.
Sonar Rate and Sequence
The sonar firing rate is 25 Hz (40 milliseconds per
sonar) and sensitivity ranges from 10cm (6
inches) to more than 5 meters (16 feet). Objects
closer than 10cm are not detected and return
an out-of-range value (> 6 meters).
You may control the sonar’s firing pattern
through software (see Chapter 5,
AmigOS
); the
default is clockwise in sequence starting with the
side sonar (#0) closest to the left wheel and
around to sonar #7 on the back rear panel of
the robot.
Sonar Sensitivity
All eight
sonars are controlled from a single board. Although calibrated at the factory,
you may adjust the sonar sensitivity and range to accommodate differing AmigoBot
operating environments. The sonar gain control is a one-turn screwcap accessible
through an access hole on the top and near the front of AmigoBot. You may have to
remove an accessory to uncover the hole.
Using a flat-bladed screwdriver, turn the adjustment screw counterclockwise to make the
sonars less sensitive to external noise and false echoes. Low sonar-gain settings reduce
the robot’s ability to see small objects. Under some circumstances, that is desirable. For
instance, attenuate the sonar if you are operating in a noisy environment or on uneven
or highly reflective floor
a heavy shag carpet, for example. If the sonars are too
sensitive, they will “see” the carpet immediately ahead of the robot as an obstacle.
Increase the sensitivity of the sonar array by turning the gain-adjustment screw clockwise,
making the sonars more likely to see small objects or objects at a greater distance. For
instance, increase the sonar gain if you are operating in a relatively quiet and open
environment with a smooth floor surface.
Serial and Accessory Ports
System Serial Port
Plug your Amigo
LEASH
cable into the telephone connector-like RJ-11/12 System serial port
on the bottom of AmigoBot and its serial adapter connected to your PC to reprogram
AmigOS-related operating software, sounds, and parameters.