Author Topic: Any recommendations for a local positioning system?  (Read 994 times)

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Offline murrdpirateTopic starter

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Any recommendations for a local positioning system?
« on: January 10, 2012, 02:58:30 PM »
Hi,

I am working on a project that will involve multiple robots carrying heavy items for humans.  I need to develop a system that will accurately monitor the position of each robot (probably to within about 20 cm).  The environment will be known beforehand, but can be quite large (~200 square meters or more).  It will be outdoor and line of sight can easily be maintained.

A few methods I've been going over:

Acoustic trilateration
GPS combined with RF phase difference measurements
Burying a grid of RFID tags and measuring strength of signal
Computer vision triangulation

I'm pretty confident that the computer vision triangulation would work well, but might get expensive.  If anyone has an suggestions, I'd be very grateful.

Offline newInRobotics

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Re: Any recommendations for a local positioning system?
« Reply #1 on: January 11, 2012, 02:40:39 AM »
If paths are known beforehand and they would not change, You can use line follower technique.
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Offline Soeren

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Re: Any recommendations for a local positioning system?
« Reply #2 on: January 12, 2012, 08:32:23 AM »
Hi,

The environment will be known beforehand, but can be quite large (~200 square meters or more).
Large? It's just about half the size of an NBA basketball court ;)


Acoustic trilateration
Too many ways it can go wrong IMO.


Burying a grid of RFID tags and measuring strength of signal
Signal strength is a poor indicator, as it will depend on the depth, the "quality" of the dirt, moisture content, mineral content etc. so will most likely vary from one place to another, even in between two tags and the cheap old RFID's won't carry more than 10..20cm in free air, so when you add dirt, they'll be close to unreadable unless you're close (i.e. right above it).

Better bury a grid of signal carrying wires then - cheaper, easier to layout precisely (although may be a bit more work actually getting into the ground, if you have to do it alone by yourself) and a lot easier to read (which makes the "receiver/reader" cheaper as well).

With the 20cm precision you need, you can use odometry for positioning and correct/reset the measurements each time a wire is passed (X and Y). With 5m between each wire in the grid, your 20 cm tolerance equates to 4% and that should keep the odometry readings well in check.


Computer vision triangulation

I'm pretty confident that the computer vision triangulation would work well, but might get expensive.  If anyone has an suggestions, I'd be very grateful.
GPS, with the precision you want, will be expensive as well.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline murrdpirateTopic starter

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Re: Any recommendations for a local positioning system?
« Reply #3 on: January 18, 2012, 06:24:22 PM »
Oops, meant to say 200x200 meters!  I appreciate the feedback.  Any thoughts on the vision triangulation?

Offline Chewy

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Re: Any recommendations for a local positioning system?
« Reply #4 on: January 20, 2012, 01:21:13 PM »
Hi Murrdpirate,

  For vision triangulation, consider Fiducial detection using RoboRealm (see http://www.roborealm.com/help/Fiducial.php).  Quite easy to use and with a higher resolution camera should be capable of meeting your 20 cm precision requirement.

  Also, consider using GotABot (see http://gotabot.weebly.com/) as an additional aid.  It can provide mapping, path planning, localization and other capabilities for your application.

    Cheers

 


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