Re: [mowbot] Still Mowing By Hand?

Terry Pearson (cefpearson nospam at
Tue, 1 Jul 1997 04:31:03 +0100

At 11:13 AM 6/30/97 -0600, you wrote:
> Greetings MowBotHeads :)
> I know everyone is very busy, but someone must be making progress.
> How about some traffic on this list again.
> Thou Shalst Mow, Hence I Shall Not

I just tested my newest version of a mowbot a few minutes ago.
I tried to keep everything very simple and use parts that can be found
everywhere. I have two GM windsheild wiper motors directly attached to two
8 inch wheels. The wheel are a 3 inch section of 6 inch PVC pipe with the
tred of an automobile tire wrapped around it and held in place with wood
screws. The mower moves at about 1 foot per sec.. The nice thing about the
wiper motors is that they had the correct rpm and torque so I did not need
to fool with gearing or another shaft and set of bearing. Also they were
cheap, 5 dollars US apeice, used. Although I had to buy three to get two to
work. The bad thing is they use a lot of power. 1.85 amps apeice with no
load. I need the power for my yard because most of my yard is on a 15
degree slant. The wiper motors can climb the hill but they draw about 9 amps
together to do it.
For the platform to mount everything on, I took 4" PVC pipe; heated it to
250 degree F; sliced it in half while hot; and flatened it between plywood
untill cool. Makes a nice 12" x 12" platform because I can use wood screws
to fasten things on to it and it's easy to cut and file.
The cutting motor is an air blower motor from a car. $2.00 US, used. It
draws 2.8 amps with no load. I use a 4" PVC disk with two 1" blades attached
to it for the cutter. The blades are sharpened end peices of hacksaw
blades. I used the holes on the end peices to mount them to the disk.
I tried a smaller motor for the cutter (.3 amp no load; 1.7 amp stalled).
It had little tourque but it ran at 10,000 rpm. It did cut grass, but it
was easily loaded down to almost a stall. The blower motor never stalled
and cut a well defined 6" path through 4" wet grass and thatch to 2". The
disapointing thing is that it takes 14 amps total for all three motors to do
this. 7 amps on a level surface, cutting no grass
I use a 12 amp hour 12 volt garden tractor motor for the power supply.
The only control are two limit switches on the front. when it hits
something it: stops, backs up ( one wheel backs up a random amount so it
turns), stops, then forward. I used 3, 555 timer chips for the control, a
quad nand gate to shape the limit switch input, and 4 relays to work as a
H-bridge and power control. Normaly off for the relays is the foward mode.
If the grass is kept short, the average current draw may be around 10
amps. The recomended carging current for the batteries is 2 amps. I have
seen resonably price solar panels that can put out 2 amps at 12 volts. still
this is a run / charge ratio of 5. Out of 10 hours of strong sun, I could
get 2 hours of cutting a 6" wide path. With a random pattern, does anyone
know how much I can cut a day?

Does anyone else have current draw figures for their robot mower?
Cef Pearson (Terry)
cefpearson nospam at
Clinton County, Indiana