MATERIALS
R/C transmitter and receiver that outputs a servo
signal. Most do. I bought an ESky EK2-0420A
6-channel set on eBay for $50.
FOR THE R/C AND FAIL-SAFE CONTROLLERS:
ATmega168 IC chips with Arduino Bootloader ( 2)
part #DEV-08846 from SparkFun (
sparkfun.com)
Other components are available from
radioshack.com.
Small pieces of perf board ( 2)
Insulated stranded wire, 22 gauge
28-pin sockets ( 2)
LM7805 voltage regulators ( 2)
16MHz crystal oscillators ( 2)
5V 1A SPDT switches ( 2)
Capacitors: 0.1μF ( 2), 220μF ( 4)
1kΩ ¼W resistors ( 6)
12V toggle switches ( 2)
Screw terminal blocks: 2-contact ( 19), 3-contact ( 2)
6× 1 female pin headers ( 3) for the R/C
LEDs, any color ( 4) 3 for the R/C
330Ω ¼W resistors ( 4) 3 for the R/C
1N4001 1A diode for the fail-safe
12V 60A normally open automotive relay $6
40A–60A fuse for the fail-safe
FOR THE MOTOR CONTROLLER:
All components are available from
digikey.com.
P-channel MOSFET transistors, 47A 60V ( 12)
Digi-Key part #FQP47P06
N-channel MOSFET transistors: 52A 60V ( 12) and
200mA 60V ( 4) parts #FQP50N06L and #2N7000
47Ω bussed resistor networks ( 8) #4606X-1-470LF-ND
2-position screw terminal blocks ( 6) #ED1609-ND
Resistors: 4.7kΩ 1W ( 24) #CF1/84.7KJRCT-ND
PC board, 1-sided copper-clad, 3"× 4½" #PC9-ND
Capacitors, 1,000μF or similar ( 4) #P5575-ND
LED, 3mm any color
Resistor, 330Ω–1kΩ ¼W for the LED
80mm PC cooling fan
TO-220 heatsinks, bolt-on or clip-on ( 24) (optional)
#8 bolts, 3" long ( 4) with matching nuts ( 12)
Power distribution block (optional) helps with wiring
FOR THE DRIVETRAIN:
Wheelchair motors ( 2)
Sprockets: 17-tooth ( 2) and 65-tooth ( 2)
part #G13610 from
goldmine-elec.com and
part #127-12 from
partsforscooters.com
Functional Overview
Basically, if you took the wheels and handlebar off
any old gas-powered push mower, bolted it into
a sturdy metal frame with 2 electric wheelchair
motors, and added the electronics needed to make
it move, you’d have the Lawnbot400. I control
mine with a standard hobby R/C transmitter and
receiver, but with just a few modifications it
#25 roller chain, 10', with 2 universal links about $12
Drive wheels with bearings ( 2) part #36054 from
Harbor Freight Tools (
harborfreight.com)
FOR THE MOWER AND CARRIAGE:
Gasoline-powered push mower about $50 used
12V sealed lead-acid marine batteries ( 2) $20–$50
Metal stock, 36" lengths: 1"× 1" angle iron ( 2); 2"× 2"
angle iron ( 2); 1"× 1" square tubing ( 2); 1" flat steel
$6–$8 each from Home Depot
Threaded rod,
3"× 36" long ( 1) with matching nuts
and washers ( 6)
½" bolts: ¾" long ( 20) and 2" long ( 10) with
matching nuts, washers, and lock washers
Caster wheels ( 2) Harbor Freight #38944, $15
Scrap of plywood to carry the electronics
TOOLS
Drill press or electric drill, with ½" bit
Angle grinder and Dremel rotary tool
Voltage meter, wire strippers, and electrical tape
Ratchet set, Allen wrenches, and crescent wrench
Pliers, screwdriver, measuring tape, and level
Welder (optional) but handy
FOR MAKING THE MOTOR CONTROLLER PCB
(OPTIONAL):
Laser printer, magazine paper, clothes iron, acetone,
Scotch-Brite cleaning pad, paper towels
Bowl of warm, soapy water
Hydrogen peroxide and muriatic acid for etchant
Glass baking dish or other shallow glass container
large enough to hold PC board
Toothbrush or air pump
Chemical gloves and safety goggles
SUBSTITUTIONS
Here are easier (but more expensive) options for
some of Lawnbot400’s major components.
» R/C controller: Arduino Duemilanove $35 from
Maker Shed (
makershed.com)
» Fail-safe controller: Arduino Duemilanove
» H-bridge motor controller: Sabertooth 2× 25
$125 from Dimension Engineering (dimension
engineering.com), or any other motor controller
that accepts a standard 0V–5V signal
» Drivetrain: Pair of wheelchair motors with wheels
already mounted to them
could be made autonomous.
Steering the Lawnbot is simple. Move the left
control stick up, and the left wheel moves forward.
Move the right control stick back, and the right
wheel moves backward. Both sticks forward and you
go straight ahead. This is called “tank steering,” and
it gives the Lawnbot400 a zero turn radius (Figure A,
following page).
43 Make:
