[mowbot] Using Ultrasonics to detect grass, concrete.

Dave Everett (Deverett nospam at vir.idx.com.au)
Wed, 25 Sep 1996 16:25:20 +1000

Ron Woodward wrote:
> >if the sensors are fixed to a permanent height portion of the mowbot
> >(like
> >inline with the axle) as we are only reading the strength of a
> >continuous
> >train of pulses.
> I do not think that a sonar system will do much good trying to detect the
> height of the grass. Grass is soft and would not reflect sound very well.
> The blades of grass are small and widly spaced relative to the sound waves.
> Using some kind of optical sensor seems more likely to work.

It was not intended for measuring the height of the grass. It was
intended to
detect the difference between soft surfaces, like grass, and hard
surfaces, like
concrete pathways etc.
> Why not use three optical sensor/emitter pairs located about 1 inch away
> from and in between both of the front wheels just slightly above blade
> height.The inside of the wheels is painted white. Two pair face out towards
> the wheels the other pair gos from one to the other. Crude Diagram follows:

We are currently discussing this type of sensing, except with a few more
to give more information.

> To ensure complete coverage the MowBot just keeps the grass between
> the center pair and no grass between eather the left or right pair.

We need a FAQ badly, anyone volunteering to cull the info from the
accumulated posts
so far?
> This is kind of what I do when I mow. Have one wheel run just outside
> the unmowed area. This should work well for following the cut edge
> but won't do much for general navigation.

Dave Everett.