MFCU Installation

FCU/mFCU User Manual
Last rev. 08/10/2022

Gorilla FCU and mFCU are control units studied for almost any traditional HPA system that responds to the needs of those who are tired to make very long settings and endless test, but above all to facilitate all those complex settings.
Every single piece is tested manually to provide the best possible service.


Gorilla FCU allows you to replace the FCUs of all the most widely used HPA systems on the market, whether they are single solenoids or the more complex double solenoids without removing functions but even adding new ones!

It allows to control the fire mode of the SEMI or the AUTOMATIC, of every HPA system (for some systems Gorilla Trigger Board is required or alternatively a compatible one like the Polarstar or Redline).

It is also tested to work on rainy days without any problems, avoiding damage.

The FCU connector allows you to connect it directly, without any modification, to all Polarstar products as well as to Redline N7 and SR-E.


Download and install "Gorilla FCU" application from the Android or Apple store and turn on Bluetooth. The first time you start, you will be asked for permission to use Bluetooth and coarse location (Android only, mandatory for using Bluetooth from version 6.0 onwards). After accepting the permissions, you can press the "Connect" button and choose your peripheral.
By clicking on the name of the device we could connect to it.


It’s really easy to install our mFCU on your build: just insert our selector plate, lock the board to the gearbox with only one screw and glue the trigger magnet holder to your trigger like in the pictures below.


We suggest to use a Maxx trigger for the best compatibility and easiest installation.


It can be possible that you need a custom installation of selector magnet or trigger magnet, like for example on ambidextrous fire selector builds where our selector plate can’t be installed. Please be sure that magnets will be placed and will move like shown in the picture below.

TRIGGER MAGNET: Its really important that, on trigger released, magnet will be between A and B position. B is just as reference while it’s mandatory that the magnet will never be placed before A position. Trigger magnet is black varnished on a face: this face is the one that have to point to the board. If your magnet position will not respect the placement on A or will be inverted on its face, mFCU will have issues.

SELECTOR PLATE MAGNET: On the other side of mFCU you can see a hole between A and B position. This hole is the back side of selector plate Sensor and is for installing reference: magnet have to stay between A and B on all selector plate Positions. This magnet can be placed without giving attention to the face that point to the board. Putting magnet too far from sensor will give issues.

BUILDS WITHOUT FIRE SELECTOR: Some professional speedsoft builds haven’t the fire selector. Using our selector plate check that magnet position will cover the sensor hole (in the middle between A and B position) than save SAFE position on the application. Without moving the selector plate save also your wanted trigger fire position using SET SAFE button as described below. Now you can remove our selector plate (or lock it far from sensor) and install your gearbox in the build. Remember that any time you want to tune the trigger fire position, your build have to be on SAFE or you will not be able to save it.


When your mFCU is properly installed on your gearbox you have to follow these short steps to get it working.
With battery plugged, connect to the mFCU and wait until it’s parameters will be read; now move your fire selector on FULL AUTO and push SET AUTO button on the application, then push SAVE on the message you got.

To save the SAFE position, move fire selector on SAFE position than push the button SET SAFE and again SAVE it.
You are now ready to tune your trigger: remember that trigger can be tuned just on SAFE position for obvious security reasons.
We strongly recommend to make this step with the trigger totally free to move along full stroke: when done you can adjust your trigger’s grains and make it really sensitive.

When on SAFE position push SET TRIGGER button; move and hold your trigger to the position you want it will fire and just now push SAVE button.
You can release the trigger and your build is now fully working.


With the FCU powered (LIPO 2s), after connected, in a few moments you will receive a notification "Settings read successfully": this means that the connection was successful and that the application have read the values ​​of the control unit.
Remember that to make effective any settings you have to push the WRITE button.

Below all parameters explanation.

Preset01: This text can be changed with your own preset name: for preset we mean a configuration file in which all the values ​​of the FCU parameters are present, at the time of saving; It is very useful if different settings are used depending on the occasion, for example for high ROF, or for maximum precision in DMR and change them in an instant without having to set value by value individually.

“EXPORT AS” button: By pushing the button labelled EXPORT AS (preset name) you will save the current configuration with the name you have chosen before in the preset space.
Below this button there is a little scroll menu where all saved presets are shown.

If all goes well you will receive a notification: "Preset exported!".
“UPDATE” and “DELETE” buttons: These 2 buttons are referring to presets. If pushed it will “UPDATE/DELETE” the selected preset.

FCMode: This value is very important because it tells the control unit how many solenoids are used in the HPA system:
0 = single solenoid systems (jack, N7 etc.)
1 = double solenoid systems (Polarstar Fusion Engine or F2)
CBMode: Allows you to select the firing sequence, where:
0 = Open bolt sequence
1 = Closed bolt sequence
In double solenoid setup with open bolt, the system’s operation order is this:

Nozzle Dwell => Nozzle Delay => Poppet Dwell => Poppet Delay
In double solenoid setup with closed bolt the order is this:
Poppet Dwell => Poppet Delay => Nozzle Dwell => Nozzle Delay
In single solenoid setup open bolt and closed bolt nozzle value will not be used and fire sequence will be:
Poppet Dwell => Poppet Delay
In the following paragraphs we will better explain how to set these values.


Magazine Counter: This function, if active, will disable the fire when the FCU reach the setpoint number of shoots. To resume hold the trigger for 3 seconds.

It allows you to simulate mid / low cap magazines even if one with higher capacity are mounted, moreover if you set as value the real magazine capacity you will avoid empty shoot.
Putting 0 as value the function is disabled.

Semi BB to Fire: (Burst mode on semi position) The set value says how many shots will be fired with a single trigger pressure when you are on SEMI. If the value is 0, the parameter is disabled. If you want to use Dual Trigger keep it to 0.

Auto BB to Fire: (Burst mode on auto position) The set value says how many shots will be fired with a single trigger pressure when you are on AUTO. If the value is 0, the parameter is disabled.
Friction Timer and Friction Value: Usually not needed with proper values on a replica, it may be necessary to set a higher poppet dwell value to overcome static friction. Static friction is a physical phenomenon that, after a period of ina

ctivity, will cause a loss of performance on your first shoot.
If you notice that after few minutes the first bb have difficult to be fired or comes out weak, it could be static friction.
Chose after how much seconds from last shoot (Friction Timer) your Friction Value will be added to your Poppet Dwell (just the first shot)

Put both these values to 0 to disable this function.

SEMI and AUTO: On some parameters you can read the words SEMI or AUTO as prefix: depending on fire selector position, FCU will use one or other parameter. When your gun is on SEMI, FCU will use the SEMI parameters otherwise it will use AUTO ones.
Poppet Dwell: It is one of most important parameters and it say how many tenths of a millisecond the related solenoid will stay activated. We suggest never to set a value less than 30 to avoid missed shots and other problems.

PLEASE NOTE: On 2 solenoid system it is the air that fire BBs while on single solenoid system this parameter will both load and fire BBs.

Because of this, it’s FUNDAMENTAL to understand the nature of the system itself before tuning.

Guide to choose the correct poppet dwell value:
Starting from the simplest case in which we are using a Wolverine Reaper or other fixed air chamber HPA Engine, we suggest to put Poppet Dwell at 255 than set your pressure regulator to have the wanted output power.

High Poppet Dwell on fixed air chamber engine will not affect air consumption. If you got some feeding problem decrease the Poppet Dwell. If you want a higher rof or more reactivity on your replica, decrease Poppet Delay and Poppet Dwell. If you decrease too much the Poppet Dwell you will see the power decreasing: this means that air got no time to fill the chamber, so your Poppet Dwell value need to be increased.

For Polarstar Fusion and all double solenoid engine:
Starting from a high Poppet Dwell value, using a chrono, lower the value step by step until you notice that all the bbs have a very similar output value. Start with large steps to go down even of one unit at a time when you are close to the optimal value. If you notice that decreasing Poppet Dwell also decreases the power, increase it back until the firing power returns to the average value.
Correctly setting this value allows you to use the right amount of air, avoiding waste and obtaining constant firing and an increased precision.

Nozzle Dwell: Another fundamental value is Nozzle Dwell. Expressed in milliseconds, it indicates the time required to load the bullet into the hop-up chamber. It is used only on 2-solenoid systems.
Its value depends very much on the BBs and magazines used. We suggest never to go below 8 to avoid the risk of jamming or other BB loading problems.

Poppet Delay: It is a wait value expressed in milliseconds, a low value is useful for having higher rof or reactivity, but often at the expense of precision. It should never be set to 0 or too low. If the replica fails, increase this value.
We suggest to never set a value less than 4.

Nozzle Delay: It is a wait value expressed in milliseconds, a low value is useful for having higher rof or reactivity, but often at the expense of precision. It should never be set to 0 nor too low. If the replica fails, increase this value.
We suggest to never set a value less than 4.

Estimated ROF: This value is an estimated prediction of the maximum value of ROF (rate of fire) and say how much BBs will be fired in the period of 1 second. This is automatically calculated changing all parameters referring to AUTO fire mode.

Total Fired BB: It is the universal counter of shots fired since the control unit was installed. It cannot be reset. Useful for those who buy used products, to check how much has been used.
Partial Fired BB: Indicates shots fired since the last reset. It can be used for various purposes, such as knowing how much you fire in a single gameplay.

FCU State: Shows the status of the FCU. If unlocked the parameters are modifiable, if locked it blocks every modification until the timer expires.

Dual Trigger: If activated, the rifle will fire at both the trigger pressure and its release.
If Semi BB to Fire is different from the value 0, the latter will prevail and Dual Trigger will never be active.

RAMP: RAMP feature comes from paintball and let you to fire slow on SEMI mode. When firing speed increase and reach a preset threshold, the rifle will start firing on FULL AUTO mode while cadence remain the same: if it decreases, rifle will return on SEMI mode.

Inverted Fire Mode: It switch the working mode between SEMI and AUTO selector: SEMI become FULL AUTO and the other way around.

Led Output: You can disable the external power supply using this checkbox, available just on mFCU.
READ button: It allows to read the values ​​set on the FCU, when pushed you will receive a notification "Settings read successfully!" and at the same time, the parameters set will be shown on the application.

RESET COUNTER button: When pushed it will reset the Partial Fired BB to 0 and will popup the message: "Partial counter resetted!".
WRITE button: Once you have made your settings you will need to press this button to save them to the control unit and make them effective. You will have confirmation of the successful saving with the notification "Settings written successfully!".

Hours to Lock: Allows you to choose how many hours to lock the FCU settings.

TOURNAMENT LOCK button: When pushed you will be warned before locking the FCU (for the time you chose in Hours to Lock). If accepted, FCU parameters will be locked. ATTENTION: THE ONLY WAY TO RESTORE NORMAL OPERATION IS TO LEAVE THE FCU CONNECTED TO THE BATTERY FOR THE REMAINING NUMBERS OF HOURS.


This schematic will allow you, with a minimum of knowledge, to adapt Gorilla FCU on any HPA system.

1 = Common positive +5V
2 = Triger switch: closing this contact to +5v positive will fire the BB
3 = Full Auto Switch: closing this contact to +5v positive will activate the Auto Mode
4 = Poppet Power Supply: this contact and +5V common positive will power on the Poppet Solenoid
5 = Nozzle Power Supply: this contact and +5V common positive will power on the Nozzle Solenoid
6 = It’s a trigger driven negative voltage
7 = It’s a direct battery positive voltage
8 = It’s a direct battery negative voltage
Regarding 3 pins port to power the LED tracer, just wire it using 6 and 7 respecting the polarity. Leds will shine until the trigger is pulled down.
Allowed connectors are JST ZH 5Pin and JST ZH 3Pin.


To increase FCU’s durability and to avoid any type of problem, please use the following precautions:
1) Use 2S Lipo premium batteries.
2) Do not leave the control unit exposed to the sun or high temperature for long periods.
3) Keep the control unit as far as possible from water and moisture.
4) Disconnect the control unit at the end of the game.
5) Do not use batteries with low charge to avoid damaging them.
6) Connect and disconnect the control unit gently.
7) If you got some issue with your FCU please read again the manual or contact us anytime.
8) After 5 minutes Bluetooth will disable itself. To restore Bluetooth connection, keep the trigger pulled for 8 seconds when on SEMI or unplug the battery. (Since FCU v3.4)

Gorilla Airsoft always try to do its best continuing to improve his products and being always present on customer support channels for any needs.