Polar Star pr-15 Fire Control Unit (FCU)

The Fire Control Unit is the brains of the polarstar fusion engine.  It controls how fast the solenoids cycle, how much air is release per shot, how long the nozzle is held to the rear, how far the nozzle travels etc..  Many individual variables will affect tuning your FCU, because of this FCU settings will be largely unique to the individual.  I hope to provide you with some information that will make the process a bit easier.


Operating the FCU is extremely easy.  There is a small "D pad" style joystick in the upper left of the unit, and a LCD that will show you what setting you have selected and the current value.  To start with the unit will be in a operational state, and the LCD will display the word "Shot".

Once you press the D pad the LCD will switch to displaying "SAFE", in this mode you can not fire the unit.

Press the D pad left and right will select a setting.  Once you have a setting selected pressing the D pad up and down will adjust that setting.  Once all your settings are to your liking press down on the center of the D pad again and you will be back in a firing state.

** side note:  I have used two MosFett controlled systems in conjunction with my AEG.  Both of them used a complex system of trigger pulls and motor vibrations to program the unit.  Compared to that .. this is a piece of cake.

Lets have a look at the settings and what they do, default settings are in parenthesis.

db (00):  Filters out electrical noise on the trigger.  I have not had to adjust this, however if you are running your FCU wires close to other wires (lights / lasers etc..) you may need to use this function.

cb (off): Closed bolt operation (on / off).  I personally like having this feature ON.  Basically it makes the first action of a firing sequence the release of air , then the cycle of the nozzle.  Meaning if you have a BB in your hopup you will shoot that BB before cycling the nozzle and loading another BB.  Likewise if you do not have a BB in your hopup you will dry fire before loading a BB.

dr (22): Return to battery delay.  How long to wait for the nozzle to move forward and chamber the next BB into the hopup.  This comes into play after the dn setting.

rf (12): Rate of Fire.  Delay between shot cycles.  The lower your number the higher your rate of fire will be.  You can safely pull this value all the way to 01.

dp (20): Poppet Dwell.  Affects the amount of time the firing valve is held open.  A higher number here will put a larger volume of air behind the BB.  This is a extremely important value for accuracy and distance. The longer your barrel the higher you should set this.  With a larger volume of air behind your BB you can continue to accelerate your BB all the way down your barrel.  Each increment here adds 0.1 ms, and there is a base value of 2ms.  So the default value of 20 means 2ms + (0.1ms * 20) = 4ms total time open.

dn (12): Nozzle Dwell.  How long the nozzle will be held back while waiting for your magazine to feed the next BB.  If you have new magazines that feed fast you can drop this value until you start seeing misfires.  For my new PMAGS I set this to 10, for my older magazines I have to bump this value up to 15.  If you are seeing a bunch of misfires .. start tweaking this setting higher.

fa (fu): Full auto.  Sets full auto or "burst" mode.  Default is full auto, meaning in full auto mode you will shoot BBs until the trigger is released.  You can also select a numeric value here 01 - 09.  If you have a setting of 05 every time you pull the trigger in full auto mode you will cycle 5 shots.

re (11): This is not a setting. This displays the revision of the firmware installed on the FCU. The up and down arrows will display the shot counter.

In the intro I said that the tuning of the FCU will depend on many individual stats, and will be unique to each weapon.  To demonstrate this I have the same settings on the FCU, but swapped out the barrel. To keep things simple assume that the following settings are always set DB:00, CB:ON, RF:01, FA:FU and only the values in the table change.

barrel (mm)	psi	BB weight	DR	DP	DN	FPS	RoF (bb/s)
290	100	.25	19	20	12	385	26
370	100	.25	19	20	12	360	26
370	100	.25	19	30	12	380	26

As you can see with the longer barrel I was actually getting lower fps, until I increased the DP value.  This change kept the firing valve open for 1ms longer with each shot and kept the BB accelerating all the way down the barrel.

I hope this page helps.  I will attempt to keep a log on the bottom of this page with any FCU settings and their performance.  If you would like me to add your setting just send me a e-mail.

barrel (mm)	psi	BB weight	DR	DP	DN	FPS	RoF (bb/s)
290	100	.25	19	20	12	385	26
370	100	.25	19	20	12	360	26
370	100	.25	19	30	12	380	26