The PolarStar Fusion Engine is a one-time upgrade that will provide the ultimate in performance and reliability for your AEG. The PolarStar system uses a High Pressure Air (HPA) system that replaces the standard battery powered gearbox. The PolarStar gearbox is solenoid driven and electronically controlled by a small onboard computer chip called the Fire Control Unit (FCU). All the components on this gearbox are made of CNC machined aluminum and manufactured in the USA. The PolarStar Engine provides a degree of control that is difficult to achieve with an AEG gearbox. The rate of fire and velocity can be adjusted to perfectly fine-tune the performance of your rifle. Whether you're looking for a high rate of fire, high FPS, or both, the PolarStar system can achieve the desired performance level. A small 7.4v LiPO battery is required to power the system. A blue nozzle is included and additional optional nozzles are available which provide an even greater degree of control when setting the FPS.