MACH 2001 Robot Lawnmower by Eddie Leighton

This is an extract from my web page at ...
www.geocities.com/zs6bne/myrobotlawnmower.htm


Name: MACH 2001 Robot Lawnmower

Components used:

I managed to purchase two identical second hand Nissan Skyline
wiper motors and a 12 volt blower motor from a motor scrap
yard dealer in  Potchefstroom not too far from my home in
Lichtenburg , Northwest Province , South Africa. The wheels are
standard 170 mm diameter lawnmower wheels obtained from the
local hardware store. Their traction is not all that good but
they made a good start for the robot lawnmower project. 
   

The evolution of my robot lawnmower

The various components evolved over time by trial and error ,
doing sketches here and there and somehow they all fitted
together as though they were designed as such!

The onboard computer

I used an old 386DX40 small sized computer for the "brains"
of the robot lawnmower. It's maybe a bit of an overkill but
it was simply available and I enjoy controlling the outside
world via the printer port. It is a cheap and easy method for
computer control. As can be seen above , I cut the motherboard
mounting area from an old desktop computer case for use as
supporting hardware for the video / printer port card , the
floppy disk controller card and also the 386 motherboard.

The onboard power supply

I used second hand YUASA Gel batteries which were replaced by
new ones in computer UPS systems. Two 6 volt batteries were
wired in parallel to supply sufficient power to the 386 PC
via a silicon diode to drop the voltage down to approximately
5 volts required by the PC. No fancy voltage regulation at
this stage but it must get the highest priority for the
future. The third battery is a 12 volt battery used for the
wiper motors , cutter motor and automotive switching relays
shown below. I may even add a second 12 volt battery to power
the cutter motor alone seeing this motor can draw currents
in excess of 5 amps and over 20 amps on startup!

The whole setup is not as efficient as one would like it to be ,
but this was to get something going with no unnecessary
problems to get it done. No electronic H Bridges and speed control
circuitry although I have plans to use an output of
the printer port for a software controlled pulse width modulated
signal for possible speed control when applying power to
the wiper motors and possibly even the cutter motor too. The
cutter itself will probably be in the form of a bush
cutter's blade or edge trimmer. This still has to be experimented
with.

The I/O system

All I/O control is done via the printer port (LPT1) of the onboard
386 PC. Inputs will be read from various sensors via
the input interface module when the budget allows it. 

The input interface module is basically just a biasing network for
the input lines on the printer port. The lines are
biased to +5 volts via 1 to 10K resistors and can also provide a
supply to the open collector sensor output circuitry.

The manual computer command simulator

When the PC is not running , I have a computer command simulator to
switch the motors on , off , forward and reverse to
give desired robot movements. This is simply a box of switches
interfaced to the output control circuitry.

Software development

The software is written using Visual Basic for DOS which I found
on the internet and it allows me to do event driven
programming which is a little better than using languages like
PASCAL or normal BASIC. I just have to plug in a standard
IBM PC Keyboard and Mono screen. I use a removable 1.44 Mb floppy
drive to boot the PC with DOS and load the program into
memory. Thereafter I remove the floppy drive and the program
continues normally running in the 2 Mb of onboard RAM.


The cost of my robot:

I thought it would be of interest to mention what my robot
lawnmower cost to make it a reality and it is by no means
complete. 

Chassis (Cover from an old electronics unit)   Free 

Second hand Gel batteries                      Free 

Angle iron for mounting brackets               Free 

386DX40 Motherboard + 2 Mb RAM                 Free 

Video / LPT card and IDE controller card       Free 

Additional hardware (Bolts and nuts)           R  30-00  

1.44 Mb Floppy drive                           Reusable 

Two second hand wiper motors                   R 300-00 

One second hand fan motor                      R 100-00 

Lawnmower wheels                               R 140-00 

Castors (Had to buy 4 of)                      R  60-00 

Automotive relays                              R 100-00 

Electronic components and veroboard            R 100-00 

Two Infrared TX/RX kits  (Awaiting arrival)    R 111-00 

TOTAL                                          R 941-00 

To compare internationally , South Africa's Rand is equivalent
to approximately R 7-80 to the dollar. 

Contact information 

Email is most welcome.  

I would love to share ideas with other robotics enthusiasts. I
know my robot is very primitive and still needs a lot of
attention. The important thing to do in the near future is to
replace the two balancing castors with a large third castor
to assist with movement over grass. The small ones tend to get
in the way. 

I can be contacted at the following two email addresses:
edleighton@hotmail.com or at work at eddieleighton@nwk.co.za