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One of the trickier aspects of R/C tank combat is that of fitting
a paintball marker, among other things, into the turret and getting
a full load of paintballs to reliably feed the marker while
the tank is underway and stationary. Most paintball markers use a simple
hopper design magazine to feed paintballs, but the limited height in the
turret makes such hoppers impossible to use.
The magazine shown here holds a full supply of 40 rounds of 68 caliber
paintballs, while occupying less than 2 inches of space above the marker.
More importantly, it can feed the marker regardless of the elevation
of the gun.
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The gray tubing shown is a heavy, reinforced vinyl tubing that is used as
a flexible underground electrical conduit. It is available in most home
supply or hardware stores and it is not very expensive. The tubing has a
number of benefits when used as a paintball magazine:
- the inside diameter is about 3/4", which easily fits a 68 cal paintball,
- there are no seams in the tube that would prevent a paintball from rolling
easily,
- it can be bent in a very tight circle (less than 3" diameter) without
crimping or preventing a paintball from rolling through it, and
- it can be cleaned with water if a paintball breaks inside.
The tubing is easy to cut with a knife and can be softened using a hair-dryer
or hot-air gun to fit over a 3/4" copper fitting. The tubing is mounted
to the inside of the turret using some brass braces and some wire-ties.
The tubing is mounted with a slight downslope along its entire length, with
more slope as it approaches the marker.
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Perhaps the most interesting aspect of this magazine design is the use
of a homemade wire coil to provide a flexible connection between the
tubing and the marker. This design was suggested by Will Montgomery and
it works quite nicely to allow the magazine to be mounted rigidly to the
turret, while the marker moves up and down as the gun is elevated.
The coil was made by taking a piece of 12 gauge solid electrical wire
and wrapping it tightly around a 3/4" wooden dowel.
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The coupling between the tubing and the coil is a short piece of 3/4" copper
pipe that has been solder to a 3/4" street elbow. A street elbow
has a straight piece on one end, instead of a coupling on either end, which
means that there is no seam to stop a paintball. The 3/4" piece of pipe goes
inside of the tubing (after a little heat is applied) and is held in place
with a hose clamp, to keep the elbow oriented appropriately. The
straight end of the street elbow is placed inside of the coil, which is
held in place by friction (use some duct tape if you really want to be safe).
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The connection between the coil and the marker is a little tricky. For
the most reliable feed, the coil should sit right over the breach, without
any seam that might prevent a paintball from falling into the chamber.
To that end, the aluminum feed tube that normally sits on top of the gun
was cut off and filed smooth. A round brass socket was then silver-soldered
onto a rounded over plate which matched the diameter of the barrel. With
a little bit of fitting and filing, the two pieces were married up so that
when the coil was placed inside of the coupling, the inside edge of the
coil was flush with the feed hole into the marker. A hose clamp is used
to keep the coil in the socket and another to keep the socket on the marker.
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The end of the magazine is capped off with a standard copper garden hose
fitting and a thread cap. The tubing is heated up and then pushed over
the copper fitting for a tight fit. For convenience, a 45 degree street elbow
was also used, so that it is easier to turn the end cap and fill paintballs.
To ensure that all of the paintballs move towards the marker, the end
cap is fitted with a pressure feed that uses a burst of CO2
to encourage the paintballs to move towards the marker.
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The pressure feed consists of a 10/32 inch
hose fitting that was tapped into the end-cap fitting, with an 1/8" CO2 line
attached to a CO2 supply of some sort.
A burst of CO2 can be taken
directly from the gun, by drilling a hole into the barrel and tapping it
to accept a 10/32 inch fitting. When a paintball is fired, some of
the CO2 pushing the paintball down the barrel will travel down the tube
and into the magazine, pushing paintballs down the magazine.
Alternatively, an air can be taken from a regulator attached to the CO2 bottle
used by the gun, which is controlled by a low-pressure valve (e.g., 150psi).
The valve can be tripped manually by a servo channel or by the same servo
(or a parallel servo) that fires the gun.
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