[mowbot] A heavy mower

Alex Davidson (Alex.Davidson nospam at dlr.de)
Wed, 09 Jul 1997 16:23:17 +0200

Perhaps you would be interested in my efforts at building a
computer-controlled mower.
Power: 2 12V 60 Ah auto batteries.
Chassis: A child's pedal car ("Kettcar")
Weight: maybe 80 lb. Hard to lift battery end with one hand.
Drive motor: Windshield wiper motor, 5 A, small spur gear
driving a bicycle pedal sprocket fastened to
rear axle.
Speed: 14 cm/sec, can climb any slope until the
wheels lose traction, at about 20% grade.
Computer: PC-XT 1 MHz
Command sender: 27 MHz 1/4 watt driven by serial computer output.
Steering: small motor turning 6 mm threaded shaft through a nut
on steering bar. Limit switches prevent oversteer.
Command receiver: serial decoder chip provides 8 discrete commands,
five now in use.
Location: 17 KHz pulse received by two mikes, delay measured
by computer (using parallel port) allows
Cutter: Fan motor, 35 cm. metal strip attached, ca. 5 A used.
Endurance: Hope for 3 hours.

Status: Cutter not mounted, everything else works, more or less.
Software difficult even though very simple-minded,
primitive outdoor tests in progress.

Sonar location repeatability ca. +/- one meter.
Determination of actual direction with this poor accuracy is
quite uncertain.
Motors interfering with radio reception is maddening, fixed by
extensive shielding, bypassing, etc. 27 MHz is a rotten frequency,
need much higher frequency for dependability and short antenna.

Would like to:
Install interfence-immune VHF telemetry receiver.
Use 2400 Baud instead of 110 Baud. The 100 ms command pulse
overloads the audio receiver and inhibits reception of ranges
less than 4 meters.
Increase power of 17 KHz beeper, reception uncertain at some
15 meters.
Have stepping motor for steering, so that steer position is
known and not estimated.

Cost: All junk parts up to now. New stuff would cost $300.
Best regards, Alex Davidson