Re: [mowbot] The grass keeps getting longer

david steinke (dsteink nospam at
Tue, 02 Feb 1999 13:00:33 -0800


My name is David Steinke and I am new to building domestic robots
(except about 30 years ago with my erector sets). I have been working
the past 22 years in scientific instrumentation. My goal is the build
simple domestic robots for vacuuming and mowing.

First I hope to build the mowing robot. Here is a basic description:

1: Round platform mounted on 3 wheels, 2 mounted on center axis just
inside edge, and one mounted 90 degrees from other two which could pivot
in any direction. Now the problem is should I drive the two center axis
wheels, or the pivot wheel? I want to be able to turn within itself, but
the steering mechanism for the pivot wheel (+- 90 degrees) will be more
work. If I drive the two center axix wheels in forward or reverse, I can
spin like a top.

2: I am experienced in photovoltaics. I have a 12 volt nospam at 1 amp array
that will fit onto my 15" to 18" diameter top. Should I charge up large
batteries and then run or just try to make it low power, run when it
shines, or half way in between?

3: How to cut the grass. I can make a nipping blade from exacto or
utility blades, a minature standard mower blade, a mulching blade, or
use weed wacker line. The mower blade, mulching blade, or weed wacker
line will consume lots of power, so they would require charge for a day
or two and then cut. The mower and mulching blade have suction to lift
the grass as part of being power hunger (I have kids/dogs that trample
the grass). I would need a fancy auto feed for the weed wacker line, but
it is not impossible. A weed wacker line could cut all the way to the
edge, where as the others probably could not get any closer than 1". I
also could add suction to the nipper and weed wacker line. Any

4: Control. I was hoping to keep it simple and I use the PIC's at work.
A simple bumper system to detect the edges, then rotate 120 degrees (?)
and go again. In the solar only mode, I could make the robot stay in the
sun (all my grass see's sun at some time). In the large power reserve, I
could make it go the the corner of the yard where the sun shines most of
the time with a electronic compass to charge. When fully charged, go
forth and cut.

5: Batteries: I can use either nicad or lead acid gel cells. I prefer
the nicads at work for environmental extremes, but the gel cells are
easier to maintain charge. Any preference?

I hope to use brushless motors for all the motors because I hope this
will run continuously for 5 years without my intervention. I already
have the motors, controllers, gear drives, spindle for the mower blade
to be driven by a timing belt, etc. Just have to decide on drive
confirguration and mower blade (which determines everything else).

David Steinke