The TCB is compatible with Taigen/Heng-Long airsoft units (versions with a switch on the back only), but they must be re-wired. This requires some very simple soldering. You can still use the same plug that comes with the stock Airsoft unit, so no extra parts are required. After the modification is done, the unit will plug into the RECOIL port on the TCB.
If you have one of the older Heng Long airsoft units that does not have the limit switch at the back, it won't work. In the US you can buy a replacement version from Taigen for about $10, but these should be widely available worldwide from regular suppliers.
For correct operation, make sure you select Airsoft as the Mechanical Barrel type on the Motors tab of OP Config (as opposed to the other option which is Mechanical Recoil).
See the video and photos below for instructions on how to modify the Airsoft unit.