Cybergun AK-47 PolarStar Fusion Engine Conversion

I wanted to see if it was possible to put a PolarStar V2 Fusion Engine into a V3 gearbox gun, specifically an AK-47 model, so I found a boneyard Cybergun AK-47 and tore it apart to try and determine the best way to make the Fusion Engine fit. I know PolarStar is coming out with a V3 gearbox version Fusion Engine at some point, but for those that can’t wait, here’s a way of putting a Fusion Engine in to an AK-47.

This conversion is a bit invasive on the gun, and quite a bit had to be cut up to make it all work. For the purists, the necessary changes to the AK may not be acceptable, but the V2 FE actually works very well and it fully supports all the functionality of the gun and it shoots like any Fusion Engine powered gun…top of the line performance and reliability.

The key issues to have the FE work in the AK-47 is dealing with the selector switch, the pistol grip, and clearance for the different V2 FE trigger geometry.

The selector switch was addressed by using micro switches linked to the FE trigger circuit board. The pistol grip problem required mounting braces to be fabricated. Since there is no motor cage to which is used to attach the grip, an alternate method had to be used. To still use the V2 FE trigger, the trigger area of the AK-47 had to be cut to provide clearance. I briefly considered making a custom trigger mount, but since this was a basically an experimental/prototype project, I thought I would try to make the V2 trigger work.


This picture shows the where the FE has to protrude into the trigger area, and the grip mounting screws.


A closeup view of the converted AK-47 trigger area.


Trigger area from the right side of the gun.


To hold the FE in place in the front, a hole was drilled in the mag well and a 8-32 flat head screw is attached to the front mounting hole on the FE.


To have the FE properly align with the AK hopup, a 1/16″ rubber shim was placed under the nozzle banjo fitting.


The AK-47 uses a shorter nozzle than the stock M4 nozzle, so the nozzle had to be cut down and re-chamfered.


To support the FE at the back, I drilled 1/4″ holes into the body and I pushed a dowel through the FE using the standard mounting hole right below the solenoids.

To find the right location for the mounting dowel, the proper alignment of the FE needs to be setup to match the barrel and hopup. Using a dowel (or by looking down the barrel) the back alignment point can be determined. The mounting screw hole at the back of the FE should line up with this point.


To mount the grip, two brackets were fabricated and 4 screws are used to mount the grip, on each side.




To support the safe, semi and full auto functionality, micro switches were used.The AK-47 selector lever goes from Safe, Full Auto, Semi Auto. I decided to simplify the implementation by changing the order to Safe, Semi Auto, Full Auto. This allowed a normally open micro switch connection to be used. For the Safe function to work, a mechanical safety wouldn’t work, so a normally closed micro switch was used. When the selector lever was in the Safe position, it would disable the trigger circuit, preventing the gun from firing.




The Safe switch functionality required cutting the trigger trace on the circuit board. This cut can easily be repaired by simply soldering a jumper over it, when normal trigger functionality is needed if the FE is moved to another gun.


A small piece of rubber is added to the trigger face to reduce the trigger travel. This is also needed to keep the trigger from hitting the grip since the trigger on the V2 gearbox sits in a different location than the V3 trigger.


The Fusion Engine with the full-auto and safety switch wires exiting out of the front. Note the wires are made extra long so the connectors can be hidden up in the battery space in the upper receiver.


The stock FE selector plate and safety lever have been removed. Also the lower selector plate guide needs to be removed as it prevents the FE from sitting properly in the AK-47 body.

The FE V2 trigger sits much lower in the AK-47, so the trigger guard had to be bent down a little and modified to properly hook into the pistol grip.

This shows how the trigger guard hooks into the grip.

To make room for the FE, the trigger area of the AK had to be cut.

To mount the upper receiver, the latch cutout on the back had to be enlarged to make room for the back of the Fusion Engine. I added a bolt to the upper receiver and one on the back of the FE, and used an large o-ring to hold the upper receiver in place.

The selector switch wires ar wrapped around the bolt rod, holding it in place, and it’s all covered by the upper receiver. The FCU and battery are hidden in the stock of the gun.


The AK-47 PolarStar Fusion Engine conversion was a bit of a challenge, but in the end it worked out fairly well. Some destructive changes were needed on the gun, but it was interesting to try out different methods for handling the fire selector functionality. This gun was recently fielded at an OP with 120 airsofters in attendance, it performed flawlessly all day, and the sting of a Fusion Engine powered AK-47 was felt by more than a few players!

Happy Airsofting,

– captainbingo