In previous installments, we discovered how to give our obot the “food” touch by using a pair of garden variety switches. If the robot bonks into something,
you can have it back up and steer itself away to open
pastures. Now that’s entertaining!
Yet it’s only one way for your robot to sense the world
around it. Another common form of robotic sensation is
proximity: the ability to see what’s there without having to
actually bump into it. Proximity detection is part of collision
avoidance, which takes many forms. Some collision
avoidance techniques are designed to detect objects very
close to the robot, while others are made to detect objects
several feet away.
This time, we’ll learn about an easy-to-use form of
proximity detection — ultrasound — and the way these low
cost sensors are connected and used. We’ll also discover
how to mount the sensor to a rotating turret attached to
your PropBot robot. Refer to Figure 1 for a finished
PropBot — complete with spinning ultrasonic sensor.
About Non-Contact
Near-Object Detection
First, let’s define some terms. Non-contact detection
senses objects without first having to hit them. Near-object
detection does just what its name implies: It senses objects
that are close by, from perhaps just a breath away to as
much as eight feet or more. These are objects that a robot
can consider to be in its immediate space — objects it may
have to deal with, and soon. These objects may be people,
animals, furniture, or other robots.
By detecting them, your robot can take appropriate
action which is defined by the programming you give it.
Your bot may be programmed to come up to people and
ask for their name. Or, it might be programmed to run
away whenever it sees movement. In either case, it won’t
be able to accomplish either behavior unless it can detect
the objects in its neighborhood.
There are two common methods of achieving near-object detection: proximity and distance.
• Proximity sensors only care if some object is within a
zone of relevance. That is, if an object is near
enough to be considered important. Objects beyond
the proximal range of a sensor are effectively ignored
because they are not seen. Out of view, out of mind.
• Distance measurement sensors determine the space
between the sensor and whatever object is within
detection range. Distance measurement techniques
vary; almost all have notable minimum and maximum
ranges. Few yield accurate data if an object is smack-dab next to the robot or very far away.
Collectively, these sensor types are often referred to as
range finders, though only a device that actually measures
and reports the distance of the covered range is a true
range finder.
As noted, among the most common proximity and
Making
Robots with
the Propeller
Activity Board
By Gordon McComb
Post comments on this section and find any associated files and/or downloads at
www.servomagazine.com/index.php/magazine/article/december2014_McComb.
Part 4
SERVO 12.2014 31
Gordon McComb is the author of the best-selling Robot
Builder's Bonanza and Arduino Robot Bonanza, both
published by McGraw-Hill and available in the SV Webstore.
