Re: [mowbot] Ultrasonic hardness measurement

Doug Smith (dougs nospam at
Wed, 25 Sep 1996 13:34:28 -0600

>Dave Everett wrote:
>> I set up an experimental breadboard to test the possibility of
>> differentiating between grass and concrete.
>Thats pretty interesting, but I'm not sure it practical.
>We'd have to distinguish between:
>grass and concrete
>grass and asphalt
>grass and mulch
>grass and gravel / pebbles
>grass and lettuce
>grass and flowers
>Thats why I'm so interested in 'position' technology.

The old Radio Electronics "Lawn Ranger" used used a row of IR emitters and
detectors to see where grass was located. You first had to manually mow
the yard perimeter and around anything you didn't want mowed. Then the
mower would follow the grass line. The initial manual mowing is a
downside, but it does eliminate the problem of detecting position or
surface composition.

Doug Smith  *  dougs nospam at