TIP: To prevent the axle
from slipping and spinning
in the drill chuck, use a file
or grinder to create 3 flats
on the axle, at equilateral
angles (Figure N). Re-chuck
the axle, aligning the flats
with the faces of the chuck.
these as the drive hubs, mounted in the drills.
First, you need to lock the axles to the hubs.
The easiest way is to jam the axle bearings
mechanically. Unscrew the axle nuts and
remove the ball bearings (Figure L), then
overtighten the axle nuts back down as hard
as you can. The axle should now be frozen.
“coast” against its drill. This means you’ll
need to freeze one freewheel entirely by welding the gears to the hub, making it a fixed hub.
To avoid doing this “fixie” modification, you
could also substitute a real fixed rear hub
(popular with road racers and bike hipsters),
or buy a drive sprocket like we did in the Drill
If the axle works loose, fix it permanently by
drilling and pinning the hub through the axle
(Figure M), using 6-32 machine screws and
jam nuts (or nylon insert nuts). We used
3 screws per hub to prevent them shearing
off. You could also weld the axle to the hub.
Rod scooter (MAKE Volume 21, page 108) and
engineer your own axle to mount it in the drill.
Put the axles in the drill chucks and tighten
The drills face opposite directions on the
kart, but you have your choice of how to align
the drive hubs in the drills. If you align both
hubs in the same direction, you won’t need to
do this next modification.
But we aligned our hubs in opposite directions, because that way the drills line up
much better for sitting between them. If you
do this, then one of your drive hubs must
be drivable backward, so that it doesn’t just
Photograph by Keith Hammond (Figure K)
7. MOUNT THE DRILLS AND CHAINS.
The drills drive 2 bike chains that turn the
wheels, and the gear clusters of both wheels
face the same side of the cart.
Aligning the drills is tricky — you’ve got to
fix them securely, within reach of the driver’s
hands, and so that the drive hubs line up with
the wheel hubs, without the chain twisting or
rubbing on anything. To get the most torque,
run the chain from a smaller gear on the drive
hub to the largest gear on the wheel hub, like
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