[mowbot] Mowbot

Ron Woodward (RWoodward nospam at gnn.com)
Wed, 25 Sep 1996 00:27:44

>I just realised that this will be very easy. We aren't trying to measure
>distance, just signal strength.
>On the system I built I schmitted the return signal to feed an
>I can just leave the 40khz signal running, integrate the pulses into a
>voltage and read it through one of the AD pins. The minimum distance is
>not relevant
>if the sensors are fixed to a permanent height portion of the mowbot
>inline with the axle) as we are only reading the strength of a
>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.

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:

------ -------
| W | | W |
| H |<<<<<<<]E E[>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>]R E[>>>>>>>| H |
| E |>>>>>>>]R ________________________________ R[<<<<<<<| E |
| E | _____/ \_____ | E |
| L | _/ \_ | L |
| | / MowBot Blade Deck \ | |
| | / \ | |

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

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.

Of course we could make these for large yards. Kind of a helper MowBot
that would do the rest of the yard after the supervisor Mowbot trimed
the edges!