Mechbox

A mechabox (gearbox) is the mechanical-electrical system inside AEG-type airsoft guns. It converts battery power into pneumatic force that propels BB pellets.

What is a mechabox?

Tokyo Marui developed the mechabox in 1991. The system houses an electric motor, gears, piston, spring, and cylinder inside a metal shell. When the trigger is pulled, the motor spins the gears, which pull back the piston and compress the spring. The released piston then pushes air through the cylinder and fires the BB.

There are 9 mechabox versions (V1–V9). The "version" number does not indicate an upgrade but refers to the shell shape designed for a specific gun type. The most common versions are V2 (M4, MP5, G3) and V3 (AK, G36, AUG).

Mechabox versions

V2 and V3 share most internal parts (gears, pistons, springs). This makes upgrades and repairs straightforward.

Main components

A mechabox contains three main systems:

Compression system: spring, piston, cylinder, and nozzle. The spring determines the gun's power output (FPS). A stronger spring means higher FPS.

Gear system: three gears (bevel, spur, sector) transfer force from the motor to the piston. The standard ratio is 18:1. For a higher rate of fire, 13:1 gears are used.

Control system: trigger contacts, fire selector switch, and a cut-off mechanism for semi-auto mode.

Maintenance

A mechabox needs regular maintenance for reliable operation:

Lubrication: Apply molybdenum grease to the gears. Use silicone oil on plastic parts and O-rings. Never use WD-40 or petroleum-based lubricants.

Intervals: Perform a full re-grease every 100,000 rounds or once a year. Check O-rings more frequently.

Common issues like jamming, FPS loss, or excessive noise are usually fixed by adjusting motor height, re-greasing, or replacing O-rings.

Related terms: AEG, FPS, hop-up, MOSFET, airsoft batteries