[mowbot] Lawn Ranger Articles

Dave Everett (deverett nospam at idx.com.au)
Sun, 17 May 1998 20:51:11 +1000

Reading through the Lawn Ranger articles after so many years has made me
remember why I didn't make one at the time.

The most serious issue is that the mechanical side is left virtually
uncharted. A one page drawing which shows little detail is the only clue as
to how the chassis, grass sensors, wheels, motors, batteries, cutting
mechanism and casters are constructed.
Worse still, there is an implication that the grass sensor system is self
levelling or adjusts to match the ground level, but these details also are

The sidebar in the final article mentions that technical drawings for the
chassis were available for a cost of $79 from the Author.

The electronic side is IMO rather strange. The choice of Z80 as controller
would obviously not be suitable now, considering the large number of
support and ram chips the controller board could be replaced quite cheaply
with a modern micro (the original CPU board costs $129 as a kit).

Following the CPU board is a motor-controller board which again is packed
with more chips than would be neccessary now. Each motor is Pulse width
modulated, a simple task for any micro, simply requiring the toggling of
port pins. On the motor-controller board, this job is done by tachometer
inputs, summing amplifiers, 2 D/A's to take 8 port lines and feed the
summing amplifier which then drive 2 UC3637 PWM chips which inturn switch
Mosfets to drive the motors. The motor-controller board kit cost $149.

But we're not finished yet! There is a power board required to regulate the
various voltages used by the robot. This board had among other components,
10 Mosfets and 3 DC-DC converters. The power board kit cost $149 less the
DC-DC converters.

Before any of you accuse me of blasphemy, I commend the author for having
actually built a fully functional robot lawn mower when I most of us haven't.

I have received approval from Gernsback to publish the articles online, I'm
wondering now whether it is worth my time to scan the images and type the
text in.

I will post a synopsis of the articles and what they cover, I'll answer any
specific questions you have about the articles, then we can see if there
are enough requests for me to put it online.

Dave Everett

Mowbot Project Website