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R/C Combat Vehicles

Gun Assembly

by
Jacoby Wilson and Brian Gregory

The original gun was a Splatmatic XJ40 .40 cal we purchased on E-Bay. Unfortunately, we didn't take a before picture, but here's a picture from the seller we bought it from.

The plastic casing is removed from the gun, along with the small CO2 cylinder holder which is replaced by a CO2 feed line from a larger bottle. A servo is attached to the handle to pull the trigger.

Click Photo For Enlargement (115 Kb)

A close-up of the trigger assembly. We (i.e., Brian) decided to use the grip frame for a nice mounting point for the servo. We are in the process of re-designing the trigger assemble to mount the servo below the gun body and to use a short section of bicycle brake cable to actuate the trigger in leu of the rod. The width of the trigger assembly is one of our concerns.

We turned down the barrel to allow a shroud to mimic the barrels of the scale craft and to allow a nice bushing to be installed as an elevation pivot point and mounting location for the jack-screw assembly.

Also shown here is the CO2-line connection that replaces the small CO2 cartridge provided with the gun.


The valve assembly is a two piece press fit with a set screw. The cup seal is what we were concerned about when we were pressing out the valve. But luckily we were able to remove it without impacting the cup seal. We used a small arbor press to push it out and the plunger for the 12gram cartridge was where the 90 degree elbow resides now. It was also pressed into the valve body and needed to be milled out (we had the tools available so milling seemed easier). In the process we tapped for a standard 1/8 NPT and we now have the ability to mount a 3.5 - 7 oz. CO2 tank in the hull.

A simple straight-line magazine approximately 10 inches long is used to hold the 20 rounds (40 cal) allowed in an armored car. The feed mechanism uses the wound springs from a key retract that most handymen use to hold their keys to their belt. We chose this method since tension is adjustable by how much chain you remove before you attach it to the follower and the length seems to sufficient for longer, odd-shaped magazines.

The jackscrew assembly is used to mount the gun in the turret.

Another view of the jackscrew assembly.


Click Photo For Enlargement (107 Kb)
The completed gun assembly ready to go in an armored car (as soon as we decide which one to build)

A standard lazy-susan turntable will be used to rotate the turret.

The belt and gears are our idea for turret traverse and we are thinking of mounting a modified servo (cs-80 cirrus type with external potetionmeter) to the hull and using the reduction of the belt to turn a geared collar on the turret itself. Again, as we get closer to building the hull, the design might change.