transistors and bolt a PC cooling fan on top, aimed to
draw air away from the board (Figure H, previous page).
To test your H-bridge, hook it up to a 12V power
source, following the schematic. Apply your Arduino’s 5V to each input, and use your voltage meter to
look for 12V at the 2-pole motor terminal outputs.
4. Mount the wheel sprockets.
The easy way is to find a set of wheelchair motors
that have wheels already mounted. I couldn’t
find any in my price range, so I just went with the
motors and found my own wheels. I didn’t think the
motors would be strong enough to drive the wheels
directly, so I opted for a 17: 65 chain drive.
To mount the sprockets to the wheels, I drilled
matching sets of 3 holes aligned around the centers
of the drive wheels and the 65-tooth sprockets.
Then I bolted the sprockets on and tightened them
up against the inside hubs as much as possible
(Figures I and J). I also welded the sprockets to the
hubs to keep them centered. Welding isn’t necessary, but it helps.
5. Build the frame.
I made a simple rectangular frame and suspended
the lawn mower body underneath it using 4 lengths
48 Make: Volume 22
of angle iron bolted to the mower’s original axle
holes. You’ll want to custom-size your frame to fit
your particular mower, and if something doesn’t
line up exactly, you may have to use your creativity.
Luckily, the dimensions don’t all have to be perfect.
Begin planning your frame by measuring your
lawn mower’s footprint and height. The frame’s
width should match the mower’s original wheelbase,
and its length must let the front caster wheels swing
360° without hitting the mower deck. Its height
should allow you to adjust the deck to sit at its original height range. For my frame, this meant 24" wide
by 48" long by 18" tall.
I constructed my frame by cutting, drilling, bolting,
and welding together lengths of angle iron, square
tubing, threaded rod, and flat steel. The main part
of the frame consists of 2 long pieces of 2" angle
iron that run from front to back, one on each side.
In front, these runners are bolted to 2 crosspieces
of square tubing, which in turn bolt to the mounting
plates of the 2 caster wheels (Figure K).
In back, the left and right runners are held up level
by vertical angle-iron risers that connect down to
the drive wheel axle. The axle consists of a length
of threaded rod that passes through a hole in the
bottom of each riser, held in place by nuts on either