The ASCU Gen.4 (Airsoft Smart Control Unit) is a electronic module, that makes every standard AEG with Marui type Ver. 2 gearbox, work exactly as the most expensive and sophisticated Airsoft rifles known as Professional Training Weapons. The new 4th generation unit has been updated with new software and hardware for increased reliability, durability, and ease of install. It has a 4 selectable fire modes, like 3-round burst, if the trigger is released before the third shoot in Full-Auto mode, if the trigger remains pressed the AEG will continue to fire until trigger is released. The ASCU Gen.4 system monitors the operation of the AEG in any time, and no matter how fast you tap the trigger, the AEG will always complete the full cycle, no matter if you shoot in Semi or Full Auto mode. After each shot or burst the piston will stop in its foremost position. It features an integrated Low Drain Protection, specially designed to keep LiPo batteries from damage. The ASCU Gen.4 will also stop the AEG firing if any mechanical problem occurs in the AEG, which protects the internals of the gearbox from further damage. The unit is easy to install in all AEG's with Ver. 2 gearbox, but should be installed by a skilled technician.