Motors, Wheels, and Position Encoders

ActivMedia Robotics

Each sonar array comes with its own driver electronics for independent control. Each array’s sonar are multiplexed; the sonar acquisition rate is adjustable, normally set to 25 Hz (40 milliseconds per sonar per array). Sensitivity ranges from ten centimeters (six inches) to over four meters, depending on the ranging rate. You may control the sonar’s firing pattern through software, too; the default is left-to-right in sequence 0 to 7 for each array. See the AROS chapters 6 and 7 for details.

The driver electronics for each array is calibrated at the factory. However, you may adjust the array’s sensitivity and range to accommodate differing operating environments. The sonar gain control is on the underside of the sonar driver board, which is attached to the floor of each sonar module.

Sonar sensitivity adjustment controls are accessible directly, although you may need to remove the Gripper to access the front sonar, if you have that accessory attached.8 For the front sonar, for instance, locate a hole near the front underside of the array through which you can see the cap of the sonar-gain adjustment potentiometer. Using a small flat-blade screwdriver, turn the gain control counterclockwise to make the sonar 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 sonar are too sensitive, they will “see” the carpet immediately ahead of the robot as an obstacle.

Increase the sensitivity of the sonar by turning the gain-adjustment screw clockwise, making them more likely to see small objects or objects at a greater distance. For instance, increase the gain if you are operating in a relatively quiet and open environment with a smooth floor surface.

Pioneer 2’s and 3’s drive systems use high-speed, high-torque, reversible-DC motors, each equipped with a high-resolution optical quadrature shaft encoder for precise position and speed sensing and advanced dead-reckoning. Motor gearhead ratios and encoder ticks per revolution vary by robot model. However, AROS converts most client commands and server information from platform independent distance units into platform-dependent encoder ticks, as expressed in the Ticksmm FLASH parameter, calculated as the encoder counts (4 * 500, typically) divided by the product of wheel circumference times gear ratio.

Inflate the tires evenly

or your robot won’t drive properly.

All Pioneer 3 robots now come with pneumatic tires so that you may configure your robot for differing terrains. In any configuration, however, be careful to inflate the tires evenly and adjust the respective Ticksmm and rotational Revcount FLASH parameters for proper operation. We ship with the tires inflated to 23 psi each.

BATTERIES AND POWER

Except when outfitted with the automated docking/charging system (see below), Pioneer 2 and 3 robots may contain up to three, hot-swappable, seven ampere-hour, 12 volts direct-current (VDC) sealed lead/acid batteries (total of 252 watt-hours), accessible through a hinged and latched rear door. We provide a suction cup tool to help grab

8It’s easier to remove the DXE’s Nose with Gripper attached.