Local Positioning System

Posted by Jerd King on December 14, 2005, 1:23 pm

I have always wanted to build/design a mobile robotics platform for
various tasks around the house/yard, even a contruction site. The
biggest problem that I have run into is a getting a positioning system
that will give me accurate positioning (+-2 inches). There are some
really expensive GPS systems, in the thousands of dollars. I don't
think that is realistic or cost effective to put in a robotic
lawnmower. I was trying to come up with my own system using wifi or
zigbee nodes to triangulate the position of the robot. I don't know if
this is possible for the resolution that I want or if someone else has
already tried it. Any thoughts or info would be great.

Posted by D Herring on December 14, 2005, 1:58 pm

Jerd King wrote:

> I have always wanted to build/design a mobile robotics platform for
> various tasks around the house/yard, even a contruction site. The
> biggest problem that I have run into is a getting a positioning system
> that will give me accurate positioning (+-2 inches). There are some
> really expensive GPS systems, in the thousands of dollars. I don't
> think that is realistic or cost effective to put in a robotic
> lawnmower. I was trying to come up with my own system using wifi or
> zigbee nodes to triangulate the position of the robot. I don't know if
> this is possible for the resolution that I want or if someone else has
> already tried it. Any thoughts or info would be great.

Unless you use specialized (= $$) equipment, measuring distance with RF
modules will not give you the required accuracy. The speed of light is
3*10^8 m/s; at 10' ~= 3m, the travel time is only 10 ns. Not gonna
happen. You might have better luck measuring angle and triangulating,
but few devices have tracking directional antennas and metal causes RF
signals to bend anyway.

I've seen two systems for indoor navigation, but neither qualifies as
cheap (comercially ~$2k each).

The ultrasonic systems (e.g. Cricket) measure the time of flight of an
ultrasonic chirp, much like ultrasonic rangefinders do. When the robot
is stationary and you have clear line-of-sight, these systems are
accurate within an inch or two. My experience with these systems is
that you have low measurement rates, and things mess up when the robot
is moving or nearby objects cause ultrasonic echos.
http://cricket.csail.mit.edu/

Optical systems such as NorthStar identify visual landmarks on the
ceiling in order to navigate. I've not tried this, but it seems
promising. Something similar might be done with IR emitters on the
ceiling, a B/W camera on the robot, and optical filters to only pass IR
light.
http://www.evolution.com/products/northstar/devbundle.masn

On the cheap end, I think mapping using dead reckoning and simple
distance sensors is probably the best that's available.

Later,
Daniel

Posted by Donald on December 14, 2005, 2:11 pm

Jerd King wrote:

pseudolite technology ( pseudo-satellite )

http://www.google.com/search?hl=en&c2coff=1&q=pseudolite

Posted by Jerd King on December 16, 2005, 8:19 am

I had another idea, I know that pinging a server/node is going to be
hard because the speed of Rf waves. What about AM or changing the
power output of the tranmitter i.e. you lose receiption of radio
station as you drive away. Some radio station put out 80-100 watts,
could you detect distance with 1-2 watt or even milliwatts, just a
thought.

Posted by Donald on December 16, 2005, 12:50 pm

Jerd King wrote:

> I had another idea, I know that pinging a server/node is going to be
> hard because the speed of Rf waves. What about AM or changing the
> power output of the tranmitter i.e. you lose receiption of radio
> station as you drive away. Some radio station put out 80-100 watts,
> could you detect distance with 1-2 watt or even milliwatts, just a
> thought.
>

PLRS

http://www.fas.org/man/dod-101/sys/land/plrs.htm

google has lots of hits, but I did not see any design specifications.

Google "radio position" or "radio navagition" found the PLRS

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