side. The drive wheels have built-in bearings, so they
attach onto the ends of the axle with another nut,
sprocket side in.
Angle-iron crosspieces connect the risers’ tops
and bottoms together in back, forming a box shape
at the back of the frame. Flat steel braces further
reinforce the risers by angling up diagonally from
the bottoms of the risers, near the axle, to the left
and right runners (Figure L).
6. Mount the motors.
The motor mounts were the most difficult part of
the frame to plan. The motor sprockets need to align
precisely with the wheel sprockets, but the motor
positions must also be adjustable, to set proper
tension on the chain. I mounted the motors to 8"
lengths of angle iron, which in turn bolted through
longitudinal slots in the runners, so they could slide
forward and backward before tightening down.
The angle-iron plates have 2 holes for mounting,
one in front of the motor and one behind it (Figure M).
To mark where the slots need to be, line up the mounting plates (preferably with the motor mounted) onto
the runners as far back as you can without hitting
any other bolts underneath the frame. Use a Sharpie
to mark the mounting hole positions on the runners,
then move the motors forward 2" and mark the new
positions. I drilled one hole at each mark and used a
Dremel tool with a cutoff wheel to cut out the rest.
Mount the sprockets to the motors’ shafts, using
a Woodruff key if your motors have a slotted bore.
With the motors slid all the way toward the back of
the frame, wrap the #25 chain around each motor
and wheel sprocket pair, and mark where they
overlap. Check that they’re the same length for both
sides, or else the bot won’t drive straight!
Cut the 2 pieces of chain and connect them
around the sprockets using the universal chain links.
To tension the chains, loosen the motor mounts and
slide them forward until there’s good tension on the
chain, then tighten the bolts back up (Figure N).
Now you can try generating some electricity. Connect a voltage meter to one set of motor terminals,
push the bot around, and watch the motor work in
reverse as a generator.
7. Attach the mower deck.
You need to suspend the lawn mower deck level, at
its normal working height. Make sure the mower’s
original wheels are all adjusted to their center position. Measure the wheels’ radius and subtract it
from the height of the Lawnbot frame. Cut 4 pieces