The Steyr AUG is a futuristic-looking bull pup design that is another unique platform for the PolarStar Fusion Engine. Because it’s a bull pup, the AUG has a very long barrel relative to its overall length. It also makes use of a two stage trigger for semi and fully automatic fire. The airsoft AUG gun uses a modified V3 gearbox. The trigger on the gearbox has been changed to allow a half pull to be semi auto fire, and a full trigger pull to be full auto.
Corey Lance was kind enough to send out his AUG to see if it was possible to install a PolarStar Fusion Engine. The challenge to install a Fusion Engine into the AUG revolves around solving the trigger issue. With a standard AEG trigger, it’s possible to make initial contact to cause the gun to fire, then you can push past this initial contact and trip a secondary switch to force full auto fire. With the V3 Fusion Engine, the trigger pull has a hard stop, so it’s not possible to push past it to make the gun shoot full auto.
To solve this problem small micro switches were added directly to the trigger assembly and the entire push rod mechanism used on the stock AEG gearbox was removed. This allowed the the two stage trigger to remain and actually make the trigger pull much smoother. The trigger is handled by a small SPDT micro switch using the normally closed connection points. When the trigger is at rest, the micros switch is activated. When the trigger is pulled the switch is released, which then triggers the FCU. The full auto is handled by a similar micro switch, but using the normally open connection points. When the trigger is fully pulled the micro switch is activated and the gun will shoot full auto.
The stock AEG gearbox is basically just form fit in the body of the AUG. There are no bolts or screws holding it in place. There is a mag well cradle for the front of the gearbox, and the back is supported by the motor cage. The gearbox is then held fast by a back plate under the rubber butt stock cover.
To make the V3 Fusion Engine fit within the gun, the motor cage bracket could not be used. The angle of the motor cage on the stock gearbox is different than the one used on the Fusion Engine. Instead a simple modification to the back plate and back screw on the V3 FE allowed the Fusion Engine to be firmly held in place. The back screw was replaced with a longer screw, and a spacer was used (the extra spacer found on the top of V2 Fusion Engines) to push the head of the screw further back. A matching hole was drilled into the back plate so when the plate is screwed in place, it fixes the Fusion Engine both vertically and horizontally. Also, the top plate on the back of the V3 Fusion Engine is slightly wider than the stock gearbox. This was milled down to match so it mates perfectly with the slot at the top of the AUG body.
Since the V3 trigger was not being used, it was removed along with the trigger circuit board and replaced with a mini circuit board so it would be easier to connect the trigger and full auto switches. The wires running from the front of the gun were made extra long so additional connectors can be used at the back of the gun. This will make it possible to extract the Fusion Engine by simply removing the back plate and disconnecting the trigger wires.
The last challenge was to retrofit the bolt cover. The bolt cover uses a spring loaded mechanism that clips to the top of the V3 stock gearbox. Since the V3 Fusion Engine doesn’t have the matching rail on top, the bolt cover simply zip-tied to the back of the Fusion Engine (there’s a very convenient slot already milled into the Engine). The bolt cover, like the Engine, is held in place and guided by the body of the gun, so it doesn’t require any additional bracing.
With the PolarStar Fusion Engine installed into the AUG, there is now a new bull-pup gun platform that can bring on BB slinging terror to the airsoft field!