Subject:
|
RE: Ranging techniques
|
Newsgroups:
|
lugnet.robotics.handyboard
|
Date:
|
Tue, 1 Jun 1999 17:40:08 GMT
|
Original-From:
|
Barry Brouillette <barry@sgi.comSTOPSPAM>
|
Viewed:
|
1050 times
|
| |
|
|
The GP2D02 output is an exponential curve so plugghing the a bunch of
samples into a TI calculator and solving for the coefficients gave me the
following two equations for two different sensors. G is 255 minus the
ouptut reading from the GP2D02. Note that two sensors have two different
equations. The GP2D02 is extemely consistant from reading to reading using
the same sensor. It has pretty wide variation from sensor to sensor
however. You'll need to do something like this to smooth your data.
Barry
mm = 44.1173 * 1.0128 ^ G
mm =49.3131 * 1.0114 ^ G
-----Original Message-----
From: Bob Kelly [mailto:rkelly@firstunion-reit.com]
Sent: Tuesday, June 01, 1999 11:14 AM
To: handyboard@media.mit.edu
Subject: Ranging techniques
Hello everyone...
If I may be permitted to ask your input on some of the following...
I have implemented a Polaroid sonar module and a GP2D02 IR ranging unit on a
R/C servo actuated pan/tilt mechanism. I can put in "scan_long(45.0)" or
"scan_short(45.0)" and a sensor reading 45 degrees to the right of the
centerline of the robot that supplies me with the average of 10 "hits" of
the "sonar_sample()" or "sonar_closeup()" and a GP2D02 reading at short
range.. Everything appears to work well and I am very satisfied to this
point with the progress I am making on my robot. However....
1). The Polaroid module seems to be very linear in its output, as would be
expected by the time of flight method. I am using a factor of sonar output
divided by 3636.3636 to get the range in feet. The two methods of
measurement each seem to have their own useful envelope. The
"sonar_closeup()" function is good betwee about 6" and about 2 1/2 feet. The
"sonar_sample()" routine appears to work well between 1 1/2 feet and about 6
1/2 feet. This is fine as the ranges overlap and I can write a routine to
use the correct function to provide a good time of flight range. My question
is, if the sonar is supposed to be good out to about thirty feet, why do I
get alot of "-1" returns from the sonar function out past about 8 feet? And
why, between about 6 feet and 8 feet do the readings become somewhat
inconsistent? Overall, I find the current capabilities fine for what I am
doing and the max reasonably accurate range of 6 feet acceptable, but hey,
there's always room for improvement.
2). The GP2D02 works well too and is very useful in the short range and
provides a very accurate (read: consistent) reading between about 1 1/2 feet
and 2 or 3 inches. This is excellent and fill s a gap left by the sonar.
Plus, while the software driver is active, the global value is updated
constantly. The problem is, the output of the sensor is not linear and I
want to convert the output into inches or feet so it can be used along with
the sonar output (I plan to implement some sort of comparison between sensor
readings and have what seems to be the most accurate sensor for a given
range used). I have logged the average of three readings for each inch of
range over 18 inches and have found the sensor readings have larger changes
at short ranges than for the same change in acual distance at longer
distances. I graphed the readings in excel and it is a nice, smooth and
predictable curve. I can't find my high school algebra books anywhere but I
just know there is a method of converting the non-linear output to linear
inches. (By the way, I modified the output of the sensor by subtracting it
from 238, which is what appears to be the closest range reading obtainable
before the sensor becomes unreliable - this gives me an output that ranges
from zero at close range and about 155 at long range). Has anyone had any
success at converting the output of this sensor to inches or some other
linear unit of measure? It would be very helpful if somebody assisted my
mathematically challenged self.
Thank you all in advance for your input,
Regards,
Bob Kelly.
|
|
1 Message in This Thread:
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
