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Two scooter wheels with ball bearings were used
as tension idlers for each track. Tracking tabs
on the inner surface of each track passed between
the idlers and on the outside of each road wheel
to prevent throwing track.
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This closeup shows the track passing over the
drive sprockets with the first road wheel between
the tracking tabs.
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This closeup shows the track installed over the inner
tension idler with the fourth road wheel between the
tracking tabs but the inner idler outside the tracking
tabs.
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Using two separate tension idler wheels per track
allows much easier track installation and removal, as
opposed to two idlers that are permanently connected.
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The 5/16 inch DIA idler shaft passes through two
horizontal slots in the side walls of the aft hull
and through the eyes of two threaded rod ends. The
rod ends are carried in horizontal holes through a 1
inch square aluminum tube mounted to the hull floor.
The track is tensioned by adjusting nuts on the aft
side of the square tube. The rod ends are locked
in place with lock washers and nuts on the front
side of the square tube.
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This side view shows proper track tensioning
that does not require a return roller. Note that
the framework for the superstructure is almost
invisible in this photo.
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Motor/gearboxes from Makita 6216 cordless electric 12VDC
drills carry nylon miter gears that turn the drive
shafts. The miter gears fit over steel spacers with
0.75 inch OD that were tapped to mate with the 1/2-20
threaded output shafts of the gearboxes. Two 10-32 set
screws were used in each miter gear. This photo
also shows the 1/2 inch bore flange bearings used
on each end of the drive shafts. Asymmetric
mounting of the miter gears on the drive shafts allows
CW rotation of each motor/gearbox to cause forward rotation
of their respective drive sprockets. This prevents
right/left track speed mismatch caused by motor CW/CCW
speed bias.
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Makita 6216 gearboxes have flange mounts with four holes.
Four 8-32 by 2 inch long screws were used to attach
each gearbox to the vertical flange of a 3 inch by
3 inch by 1/4 inch thick aluminum angle bracket.
The angle brackets were bolted to the floor of the
hull with a 1/8 inch thick aluminum backing plate. The motors were
connected axially to the gearboxes using the same 8-32
screws and a plexiglass retaining ring. The gearbox
speed selector wire was held in the low speed position
by washers and extra nuts on the 8-32 screws.
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