Re: [mowbot] Absolute location

Monta Elkins (Monta nospam at
Mon, 14 Oct 1996 11:07:37 -0400

Gee, what a great idea.

What about an RF "trigger" on mowbot that sets off 4-5 ultrasonic
"pings" at different frequencies from different known locations.
Mowbot cold RF triger -- listen at one frequency; RF trigger listen
at the next frequency until all stations were polled.

The multiple stations would be for when 1 or more were blocked
by a Yard Obsticle (y.o.). Time shortest response to help omit

What's the resolution of this system, (looks like centimeter
resolution would be pretty easy)?

Any trouble with omnidirectional microphones for the ultra-sonic

(I'm assuming a single RF frequency and multiple ultrasonics would
make beacon construction easier, but we could use multiple RF
frequencies and a single ultrasonic...)

I'd like some comments from folks used to using ultrasonics
(range finders etc.)


robin nospam at wrote:
> Just saw this on comp.robotics.misc. I thought the time difference
> IR/ultrasound technique mentioned might prove useful.
> Robin.
> >You can always flood the area with IR. Use many IR diodes attached to
> >an easily seen position (ceiling?).
> >
> >IS Robotics (I think) have a precise homing system that uses one IR
> >emitter, and two ultrasonic transmitters. There is a semi-intelligent
> >controller at the base that blips the IR emitter, and pings one of the
> >ultrasonic transducers. The robot picks up both transmissions, and from
> >the delay of sound, computes one distance. The base then blips the IR and
> >pings the other ultrasonic, and the robot gets the other distance, to
> >calculate its position. I guess you can calculate the orientation
> >by taking two position readings, but moving on a straight line in between,
> >and then finding out the orientation vector...
> >
> >The system is sold for thousands of dollars, but a hobbyist can probably
> >do it cheaply.

-Monta Elkins

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