View unanswered posts | View active topics It is currently Sat Aug 30, 2014 10:59 pm






Reply to topic  [ 4 posts ] 
Discussion on sonars 
Author Message
Expert

Joined: Sun Aug 19, 2007 2:43 pm
Posts: 136
Location: New Jersey
Post Discussion on sonars
Although the tests are mainly using nxt sonar sensor, I suspect this is the issue may be typical for most sonar sensors.


To obtain distance data, sonar can indeed be very problematic when the object happens not to be flat; unlike distance feedback by, say, a laser sensor.

We collect some experimental data about mapping out the reading for a rectangular box. As expected, some interesting anomaly approaching the far corners. I tried to lookup online about technical information about the sonar sensor, but unfortunately all of them are about flat object only . Any technical information about how sonar works will be helpful.

This is not a great diagram, but hope to get the idea across.
Attachment:
sonar-fd.gif
sonar-fd.gif [ 1.18 KiB | Viewed 1521 times ]


the grey area is where the sonar's feedback varies far from expected (calculated values). Calculated distance = simple trig calculation from the bottom center.


Last edited by elizabeth.mabrey on Fri Apr 06, 2012 12:03 pm, edited 1 time in total.



Fri Apr 06, 2012 11:33 am
Profile WWW
Senior Roboticist
User avatar

Joined: Wed Sep 28, 2011 10:13 pm
Posts: 630
Location: If I told you, I'd have to kill you.
Post Re: Discussion on sonars
elizabeth.mabrey wrote:
Although the tests are mainly using nxt sonar sensor, I suspect this is the issue may be typical for most sonar sensors.


To obtain distance data, sonar can indeed be very problematic when the object happens not to be flat; unlike distance feedback by, say, a laser sensor.

We collect some experimental data about mapping out the reading for a rectangular box. As expected, some interesting anomaly approaching the far corners. I tried to lookup online about technical information about the sonar sensor, but unfortunately all of them are about flat object only . Any technical information about how sonar works will be helpful.
Code:
 _____________________
|     \                  /      |
|                               |
|\       \            /     /  |
|    \               /    /    |
|        \   \     /   /       |
|            \   /             |
|_________X________|


This is not a great diagram, but hope to get the idea across.


Not to be rude, but the NXT sensor is actually a ultrasonic sensor, as in it sends ultrasonic sound waves out as opposed to the infrasonic usually used be actual sonar sensors.

Yes, Ultrasonic sensors such as these do have problems getting a distance on a curved or angled surface, as it bounces the sound waves off at an angle, away from the sensor. This is problematic, because the sensor gauges distance by how long it takes the sound it shot out to bounce back to it. This is a problem with practically all Ultrasonic sensors, especially the LEGO ones. IR Light reflectance works better, but only at small distances. As you said, Laser Rangers are by far the best, but are usually too exspensive for the common person (and kinda dangerous). The kind of sonar on submarines and such have many, many transmitters and receivers, so it is virtually surrounded by sound. Also, things such a cloth tend to absorb sound waves, causing NONE to be returned.

So, have I enlightened you at all?

_________________
A.K.A. inxt-generation
Self-proclaimed genius, and future world dominator.
My Brickshelf Folder
"Don't they teach recreational mathematics anymore?" - The Tenth Doctor
Bow down to Nikola Tesla, King of the Geek Gods.


Fri Apr 06, 2012 12:02 pm
Profile WWW
Expert

Joined: Sun Aug 19, 2007 2:43 pm
Posts: 136
Location: New Jersey
Post Re: Discussion on sonars
cool. Thanks. This definitely helps. I did not know the difference between Infrasonic and ultra sonics. That's definitely something interesting to read on.

So, with the limitation of the technology available to the kids , I would assume they'll just have to create value map for the field using the ultrasonic sensor, or they will have to make sure the sensor is facing the flat surfaces only.


Fri Apr 06, 2012 12:24 pm
Profile WWW
Moderator
Moderator
User avatar

Joined: Tue Sep 14, 2010 9:19 pm
Posts: 496
Post Re: Discussion on sonars
Take a look at the beam pattern section on this page: http://www.vexforum.com/wiki/index.php/ ... nge_Finder
It's for the VEX Ultrasonic Rangefinder, but the information still applies.

_________________
sudo rm -rf /


Fri Apr 06, 2012 12:29 pm
Profile
Display posts from previous:  Sort by  
Reply to topic   [ 4 posts ] 

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  



Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group.
Designed by ST Software for PTF.