DPRG mailing list archives: [DPRG] Placement and interpretation of ultrasonic

Fri Jun 1 12:02:40 CDT 2007

Hi Brian,

The Maxbotix sensors state having a narrower detection area than other sensors, 
but still might have the possibility of interference with each other. As a 
single transducer sensor, placement might be as easy as a simple 5 degree angle 
between the 2, as dpa's SR04 makes use of with Polaroid transducers (not quite 
parallel, but almost appearing so). Some sonar sensors need to be placed at bit 
of a height off the ground, maybe 4 or 6 inches up, to avoid any false ground 
reflections (picking up ground cracks and such). Your placement could also 
depend upon what you want to do with your robot. If just to wander around in a 
area, having both sensors facing forward (with a small angle between) would work 
to allow the robot to detect most obstacles in its path. If wall following was 
an expected, then one sensor could be aimed straight ahead for oncoming walls, 
with the other aimed to the side, to maintain a distance from the side wall. Be 
prepared to change mounting to get better results in what you wat to do. It 
might even be good to mount them on servos, so that you can have them aimed as 
the robot needs in different situations.

On crunching numbers, figure out which method you are using to read them, (pulse 
width, variable voltage, or serial data) and how the numbers could be used to 
change your motor output. You could use the returned info as just a setpoint, 
causing the robot to do some action if the numbers are greater than or less than 
a certain amount. Or you could use the changing return to produce a variety of 
responses, such as special types of turns when the numbers show the robot is too 
close to something. This could be a number of hard determinations, or the 
numbers could part af a formula that directly determines PWM to motors for a 
continuously variable response. The best would probably be to experiment and see 
what gets the response you want from the robot.

-robodave

----- Original Message ----- 
From: "Brian Clough" <bclough at banksofthesusquehanna.com>
To: "Dprglist at Dprg.Org" <dprglist at dprg.org>
Sent: Friday, June 01, 2007 8:52 AM
Subject: [DPRG] Placement and interpretation of ultrasonic

Guys:

I have two MaxBotics ultrasonic sensors, that I want to use to give the
Hexbot some "eyesight".  I need a good way to place these two sensors,
and some information on how to crunch the incoming numbers, to give the
processor a good picture of surrounding obstacles.

I don't know if I should place both facing directly forward, at slight
angles, one forward and another at an angle, or something else.

Does anyone have some general advice on this topic?

Brian

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