Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: Positioning devices

  1. I apologize if this is the wrong forum to post it in, but I'm new here(and I intend to stay beyond my initial questions)... So please put it into the right place if I'm wrong...

    What possible Positioning Devices are there for getting a robot's position with centimeter's accuracy... What possible methods can be used and what products can be bought...

    Note: This is for the ION competition, if that makes any difference

  2. #2
    Join Date
    Apr 2008
    Location
    Nelson, New Zealand
    Posts
    1,356
    Images
    58
    Rep Power
    78

    Re: Positioning devices

    Hi mattgatsi: Welcome to this forum. Is that the robotic lawn mowing competition? I was thinking NorthStar, But that is mainly for indoor navigation.
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.


  3. Re: Positioning devices

    Quote Originally Posted by 4mem8 View Post
    Hi mattgatsi: Welcome to this forum. Is that the robotic lawn mowing competition? I was thinking NorthStar, But that is mainly for indoor navigation.
    Yupp, it is for the autonomous robotic lawnmower competition... I checked the NorthStar website, but can't find any products I could use, are there any other suggestions?

  4. #4
    Join Date
    May 2008
    Posts
    2,228
    Images
    155
    Rep Power
    132

    Re: Positioning devices

    Depends what you mean by 'position'. GPS will give you the absolute postion, that is, where on the globe the robot is located, but only down to maybe 30 feet. If, on the other hand, you know where you are starting, encoders on wheels can tell you how far the wheels have moved, and from this you can extrapolate how far the robot has moved. Accuracy of encoders will primarily depend on the environment: slippery ground, carpet, etc can cause slippage of the wheels which results in inaccuracy. The farther the robot goes, the more these errors will add up.

    Do you really need 'centimeters accuracy'? Or are you looking for centimeters resolution? In the latter, you would be recording how many centimeters you think the robot has moved, but over time the count may be off more than a centimeter. For instance, if the robot is going 100meters distance, asking to be within a centimeter is asking for 0.01% error. Thats probably just not gonna happen in the real world...

    -Fergs

  5. #5
    Join Date
    May 2008
    Location
    WNC
    Posts
    413
    Images
    68
    Rep Power
    61

    Re: Positioning devices

    First - welcome to the forum!

    Seems that a laser beacon would help define where you are, the more beacons the more accurate. Sort of a local laser GPS system.
    As for the wheel encoders, if "wheel slippage" is a concern, and accuracy is imperative, I would think about a separate set of "non driven" encoder wheels, they would just free wheel on the ground (I would hang them on some sort of sprung suspension) and would be less prone to the torque slippage that would inevitably happen with encoding the drive wheels. Of course you would gain an error if the ground was bumpy, from the additional distance traveled up and down by the encoder wheel. At the end of the day though it is still "friction based", and prone to at least some inaccuracy.

    Is there a link for the mower competition???

  6. #6
    Join Date
    Apr 2008
    Location
    Sacramento, CA, USA Area
    Posts
    5,341
    Rep Power
    181

    Re: Positioning devices

    Some ideas related have been tossed around in this thread: http://forums.trossenrobotics.com/showthread.php?t=2205

    The rules for S_Oly 2009 are out and my creativitiy is being redirected there now - back-to-back gold medals are a moral imperative for my team (), so I can't think about any other competitions for the next [cough] six months or so...
    I Void Warranties�

  7. #7
    Join Date
    Apr 2008
    Location
    Sunnyvale, CA
    Posts
    378
    Images
    34
    Rep Power
    60

    Re: Positioning devices

    I've always wondered if an optical mouse could be hacked for inertial guidance. Seems like with a change of focal length it could track XY motion over a relatively flat surface.

  8. #8
    Join Date
    Apr 2008
    Location
    Sacramento, CA, USA Area
    Posts
    5,341
    Rep Power
    181

    Re: Positioning devices

    Absolutely. I don't know if grass is going to help that little camera though.

    As I understand them from having hacked on a few, the widdle high-res camera is imaging the surface looking for imperfections [as "landmarks"]. When you move the mouse, it's those little changes in position of imperfections in the surface that are encoding. I suppose changing its focal length it could probably track across grass. A scaled printout of a grass surface put underneath a mouse would probably tell you, right?

    The same thing could be done in roborealm with a high-res camera pointed down though.
    I Void Warranties�

  9. #9
    Join Date
    Apr 2008
    Location
    Sunnyvale, CA
    Posts
    378
    Images
    34
    Rep Power
    60

    Re: Positioning devices

    Quote Originally Posted by Adrenalynn View Post
    A scaled printout of a grass surface put underneath a mouse would probably tell you, right?
    Grass has a 3D structure, so it's going to depend on whether the imaging system could cope with changes of parallax.

    I think that a camera pointed down would make an excellent sensor for a lawn mower, both for measuring position and for detecting the edges of the lawn area.

  10. #10
    Join Date
    Apr 2008
    Location
    Sacramento, CA, USA Area
    Posts
    5,341
    Rep Power
    181

    Re: Positioning devices

    Even though it has 3D structure, it's only looking for microscopic pixel differences, right? I guess if the grass under the "mouse" were moving in some counter-relation to the mouse's camera, that'd suck. Like dragging a piece of paper under an optical whilst moving the mouse in the opposite direction [that's a tough experiment to conduct, but with some gnashing of teeth, I tried it and it does screw things up...]
    I Void Warranties�

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Phidget Devices
    By cmmguy in forum Arbotix, Microcontrollers, Arduino
    Replies: 10
    Last Post: 03-06-2008, 10:04 PM
  2. Replies: 0
    Last Post: 08-29-2007, 12:38 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •