Remove the gear, clean the shaft, and thread
the bearings back onto the prop shaft. Replace
the gear, fitting the pin through both holes.
Test-fit the prop shaft, gear, and bearings,
lengthwise inside one half of the gearbox
case (Figure D). To glue the rear bearing to
the shaft, slide it down the shaft, apply a thin
layer of super glue, slide it back, and replace
the shaft assembly in the case before the glue
dries. Do not get glue into the bearings.
Fit the other half of the case over the shaft
assembly and make sure the gear spins freely.
the prop shaft so the gears mesh (Figure G). Fit the second 5× 11× 4 bearing into the other case half, and close the case. The prop shaft
should spin the axle freely. Take the small
bolt and nut that come with the gearbox and
screw the halves together at the hole near the
axle using a 2.5mm hex key.
Identify the gearbox’s top by turning the
prop shaft clockwise, viewing from the back.
The axle should run the wheels (when they’re
on) away from the propeller, not toward it.
Tighten one of the gearbox’s longer included
bolts through its middle top hole (Figure H).
3. MAKE THE AXLE.
Cut a 7½" length of the 3mm ID CF tube and
drill it out with a 1" bit (Figure E). Cut two ¾"
lengths of 1" aluminum tubing and glue them
into the CF tube, leaving ¼" exposed on each
side. Use the 1" bit to drill out the hub holes
of the 3. 35" wheels so they fit onto the axle.
Mark the center of the 7½" axle with the
edge of a piece of tape, and slide the smaller
gear over the axle until its teeth lie against the
tape at the center. Use the same procedure
as in Step 2 to attach the smaller gear to the
axle in this location.
Slide one 5× 11× 4 bearing onto the axle
(Figure F). It should fit snugly. If it’s too loose,
thicken the axle with a layer of super glue; if
it’s too tight, sand the axle down with 600-grit
sandpaper. Remove tape.
5. MAKE THE BEARING BLOCK.
The prop shaft is steadied by a block of HDPE
that caps the back end of the frame tube.
The shaft runs through a 8" (or 11mm) hole
centered ½" below the block’s top 1"×½" face,
and the frame tube fits into a 2" hole drilled
¾" deep in the center of the bottom face.
If you start with a larger piece of HDPE,
you can cut the block to size before drilling,
or leave some extra length to clamp in a drill
press for drilling the 8" (or 11mm) hole. After
cutting and drilling, round the block’s corners.
6. MAKE THE FRAME.
Cut 25" of 2" OD aluminum tube and drill two
t" holes through, ¼" and 1. 45" (or 1G")
from one end. This is the frame tube.
Use a t" bit to enlarge the gearbox’s two
bottom mounting holes. Slide a 6-32× 1¼"
bolt through each, and screw a nut onto the
front bolt as a spacer. Secure the tube onto
4. ASSEMBLE THE GEARBOX.
Insert the axle bearing into the deeper half of
the gearbox case, axle running through. Fit in
58 Make: makezine.com/26