Pioneer 2 / PeopleBot - Manual (Page 19)

ActivMedia Robotics
All models come with an access port near the center of the Deck through which to run
cables to the internal components.
Sonar Arrays with Gain Adjustment
Natively, ActivMedia robots support both front and rear sonar arrays, each with eight
transducers that provide object detection and range information for features
recognition, as well as navigation around obstacles. With sonar expansion electronics,
you may add up to 16 more sonar in two additional arrays of eight sonar each.
PeopleBots, for instance, have an additional array at the front of the upper Deck.
The sonar positions in all arrays are fixed: one on each side, and six facing outward at 20-
degree intervals. Together, fore and aft sonar arrays provide 360 degrees of nearly
seamless sensing for the platform.
Figure 12. ActivMedia robot sonar array
Each sonar array comes with its own
driver electronics for independent
control. Each arrays’ sonar are
multiplexed; the sonar acquisition
rate is 25 Hz (40 milliseconds per sonar
per array. Sensitivity ranges from ten
centimeters (six inches) to nearly five
meters (16 feet). You may control the
sonar’s firing pattern through
software; the default is left-to-right in
sequence 0 to 7 for each array.
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. 7 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.
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7 It’s easier to remove the DXE’s Nose with Gripper attached.