Isnin, Mei 20, 2013

Robotic Lawnmower

Robot Lawnmower

Robot Lawnmower
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Robotic Lawnmower
Robotic Lawnmower
  • Introduction
Hi. My name is Eddie Leighton and I live in a historical small 
town called Lichtenburg in South Africa.  I enjoy designing and 
building simple electronic projects , technical computer 
programming , hobby robotics and amateur radio 
(Call sign ZS6BNE since 1975). This is a snapshot of me
 taken in February 2001 in my home electronics workshop 
and "Ham shack".
Eddie Leighton (ZS6BNE)
  • Previous robots
The first desktop robot I ever built is 
shown below. This robot has an "
Umbilical Cord" which is plugged into
 a printer port of any standard IBM or
 compatible PC. 
"ELeigh" the desktop robot
It used to have a 386DX40 onboard PC and an infrared sensor 
mounted on a third stepper motor to allow it to "Look around" 
but the Power requirement to Weight ratio was just too high 
and the stepper motors battled to handle the load.
"Eleigh" with onboard 386 and infrared detector
The coils of the two stepper motors were controlled via the 
printer port by software for the desired movements of the robot. 
This provided me with a very good basis for experimenting with 
robotics and stepper motors in general. Power was supplied to 
the coils of the stepper motors by a 6 volt Gel battery carried on 
the robot. There are also facilities for sending back five signals 
from the robot to the controlling PC printer port for sensor 
  • Humble beginnings
This is where it all started. A floor full of parts shown above. 
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 only component which I could not use for the 
robot lawnmower was the dustbin lid which was too small , 
but I used it on my first desktop robot and it gave the robot a 
nice "Turtle" effect. Although the MACH 2013 Robot 
Lawnmower (The name was derived by it's month and year 
of being built) does not look like a lawnmower that will 
eventually be it's goal.
  • The wheel mountings
Here is a snapshot of how I mounted the lawnmower wheels 
to the Nissan Skyline wiper motor shafts by means of a threaded
 12 mm bolt. This was done with the help of a friend who could
 do the necessary turning for me on his back yard lathe. 
The chassis was made from an aluminum cover taken from 
an old piece of electronic equipment. 
  • 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 new 21 Mac 2013 Model II
Robot Lawnmower
The 386 PC Controller has now been removed and will be 
replaced by a PIC16F84 Micro controller which solves the 
problem of having to boot from the floppy drive and also solves 
the power supply problem. Programming the PIC is not as 
straightforward as programming the 386 PC's printer port 
though as it has to be done using PIC assembler. (I use the 
MPLAB assembler from Microchip)
Here is an example program to send a signal to one of the 
robot's motors via the motor relay driver board. 
(5 Seconds ON / 5 Seconds OFF)     IOControl.ASM
See the table for wiring instructions to the PIC Micro controller  
  • 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 are 
wired in parallel to supply sufficient power to the 386 PC via a
 silicon diode bridge 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!

21 Mac 2013
A 7805 voltage regulator is used to drop the 12 volt supply 
down to 5 volts to provide power to the PIC Micro controller. 
An important point is the use of 33 microfarad tantalum 
capacitors on the input and output of the regulator and a 
100 nanofarad capacitor across the supply terminals of the 
PIC IC to prevent noise affecting the PIC Micro controller 
due to the switching of the wiper motors.

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. The outputs from the infrared detector kits 
are fed from the open collector transistor output to the input 
interface module. Further inputs will be read from various 
other sensors via the input interface module when the budget 
allows it. 

21 Mac 2013
See above , concerning the new PIC16F84 Micro controller.

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.

21 Mac 2013
See above , concerning the new PIC16F84 Micro controller.

  • 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
Originally  , the software was written using Visual Basic for 
DOS which I found on the internet and although it is slow , 
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.

21 Mac 2013       
See above , concerning the new PIC16F84 Micro controller. 
A program I wrote in PIC16F84 assembler to simulate all the 
Mach 2001 Model II robot movements can be viewed here.

The MACH 2013 Robot Lawnmower being programmed
 I have built a wooden stand as can be seen above under the 
robot to prevent traction of the wheels while simulating 
behaviors in response tosensor input (Stimulus). Almost sounds
 like psychology but is it at all anything else? The infrared 
detector units are not shown in this picture , but have they been 
mounted on both sides in the front , with adjustable brackets to 
be able to get the correct angle to be effective in detecting 
objects from the front and sides of the robot.
  • The cost of building the MACH 2013 Robot Lawnmower
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 + 2Mb RAM (No longer used) Free
Video / LPT card and IDE controller card       Free
PIC16F84 and programmer unit                   Donated
DC Trip switches for the 12 an 5 volt supplies Free
Additional hardware (Bolts and nuts)           R  30-00 
1.44 Mb Floppy drive  (No longer used)         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 Vero board           R 100-00
Two Infrared TX/RX kits                        R 111-00
TOTAL                                          R 941-00

To compare internationally , South Africa's Rand is equivalent 
to approximately R 8-30 to the dollar and to date 
(25 October 2001) R 9-30.
  • 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  email address:  
edleighton@hotmail.com .


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