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Old 10-19-2016, 01:31 AM
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StrayOne StrayOne is offline
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How to tune a Polarstar

Settings by PolarStar
There is a ton of confusion and misinformation going around regarding settings so I have decided to do a write up.

If your Fusion Engine stops functioning properly one of the first things that should be done is to reset the FCU to the factory default settings. This can be done by depressing and holding the tactile switch while plugging in the battery. Many times this is all that is needed to fix a problem. Even if the settings you are running work on another gun, they may not work on this particular one since every gun can behave differently depending on what components it is configured with. Incorrect settings can cause problems such as the gun not feeding/firing, jamming or terrible accuracy. Therefore you should always tune your rifle based on how that particular rifle responds.

Before making any adjustments to the FCU make sure the barrel and nozzle you intend to use are installed and set the pressure on your regulator so the gun shoots at the intended velocity. This is important since changing any one of these variables can make a difference in how the gun behaves and the FCU may need to be adjusted accordingly.

The Fusion Engine has four main dwell settings that affect performance. The order of these dwells is the same in Closed Bolt and Open Bolt. The main difference between the two modes is the location of the start point in the cycle.

The order of the dwells in a firing cycle are as follows: dn, dr, dP, rF
in full auto the cycle repeats: dn, dr, dP, rF; dn, dr, dP, rF.

Each dwell has a recommended setting and some dwells have a minimum recommended setting regardless of all other factors e.g. BBís, magazines, gun brand etc. All dwells are in millisecond (1 thousandth of a second) increments except for the dP which is in 1/10th of a millisecond (1 ten thousandth of a second) increments.

When you want to tune the FCU, the order that you adjust the settings needs to be considered. It is recommended that you start with the FCU at the factory settings.

The first setting to address is the dn setting which determines how long the nozzle is held back. Load all the magazines that you intend to use with the brand and weight BB's you intend to shoot. Select one magazine and use just that magazine for the first portion of the test. Insert the magazine into the gun and shoot about ten shots on semi and ten on full auto. If the gun feeds every single round lower the dn by 2 and repeat. Continue until the gun begins to miss feed, when it starts to miss feed increase the dn by 1 until it feeds every single round again. Burn through the whole magazine using semi and auto and confirm zero miss feeds. If there are miss feeds reload the magazine and shoot again, if there are still miss feeds increase the dn by 1 reload and shoot again until you can get through the entire magazine from full to empty without experiencing a feeding issue. Now, start working your way through the rest of your magazines to ensure you have no feeding issues with any of them. Again, shoot from full to empty as the magazines spring tension can change depending on how much ammo the magazine is pushing up. One magazine might not feed as well as another so, if you experience a miss feed with any other magazine, that magazine feeds slower and you should repeat the first test and adjust the dn to work with that magazine until it feeds properly. Once you can shoot any of your magazines without a miss feed, take note of your dn setting because this is the lowest you can take it at this pressure, using this nozzle, with these magazines and these BB's. If you are not going for the fastest rate of fire possible you will probably want to increase the dn by 1 or 2 to guarantee perfect feeding during use. You now have a base dn to start with. For this example letís say it is a dn of 10.

For the next test do not insert a magazine into the gun and be sure the gun is empty by dry firing a few shots.

Next we will look at the dP setting which determines how long power is applied to the solenoid which opens the poppet valve. When the poppet valve is opened it releases air to fire the BB. If this setting is to low the gun will not fire the first shot after sitting for a short period of time, if it is lower still the gun will not fire at all. Some guns will need the dP to be adjusted with significant changes in climate and/or geography. The dP setting is in 1/10th of a millisecond increments so any changes to it are going to have a very minor effect on the poppet valve. To start, reduce the dP setting by 2 and let the gun sit for 5 minutes. Fire the gun twice on semi and confirm that the poppet valve fires air down the nozzle/barrel for both shots. Continue to reduce the dP by 2 and letting the gun sit for 5 minutes until the first trigger pull does not fire air down the nozzle/barrel. Increase the dP by 2 and this now the lowest you can take the dP at this pressure and general climate and geography. You can increase the dP from this point to try and tune for longer barrels or heavier ammo however this will only have a very minor affect. You now have a starting dP setting, letís say a dP of 20 which is 2 milliseconds. There is also a base dP value in milliseconds that cannot be altered. This base value is determined by which revision the FCU programming is. The base dP for RE15, 16 and 17 is 2; RE18 and 19 is 2.5; RE20 is 2.7. Add the base value to what you have set the dP to be, letís say 2.5 + 2 = 4.5, this is your total dP value.

Given that you need the gun to feed consistently and fire every time, the dn and dP settings you just set are the base for any future adjustments you will make. Unless you change variables (e.g. pressure, magazines, BB's, climate) and need to adjust settings accordingly most of your tuning will be done using the rF and dr settings. The current total base value for the dn and dP example is 14.5 milliseconds.

Next up is the rF setting, the rF controls the time between closing the poppet and retracting the nozzle.
The poppet takes a certain amount of time to close and shut the firing air off. If the nozzle is allowed to start retracting while air is still flowing it will result in an air leak and a loss of power, consistency and accuracy or jamming especially in full auto. The lowest the rF should be taken is 4. Anything less than this will result in an air leak. (The next paragraph goes into more detail if you are interested, if not skip it). For this example we will leave the rF low and set it to 4.

The dP dwell controls how long the Poppet solenoid is energized, when this dwell time is passed power to the Poppet solenoid is turned off, however, the solenoid takes 2.5 milliseconds to de-energize. This means that when power is turned off to the Poppet solenoid it takes 2.5 milliseconds for the magnetic field to breakdown and to allow the valve to start closing. Once the Poppet solenoid valve closes the Poppet valve in the cylinder has to push air back out through the fittings, clear tubing and the solenoid as it closes off which takes roughly 1 millisecond. This brings the total amount of time between turning off the power to the solenoid and the Poppet valve sealing and shutting off the firing air to 3.5 milliseconds. The rF dwell begins immediately after the dP dwell ends so the rF needs to be set to a minimum of 4 to account for the 3.5 milliseconds needed to seal the Poppet valve. If the rF is less than 4 the dn dwell will start the nozzle retracting before the Poppet valve has fully closed which will result in an air leak and a loss of power, consistency and accuracy or jamming especially in full auto.

Last up is the dr setting. The dr controls the time between releasing the nozzle to return forward and firing the poppet valve. The nozzle takes a minimum of 9 milliseconds at 100 psi to return all the way forward without a BB in front of it. With the solenoid de-energize time of 2.5 milliseconds the nozzle requires no less than 11.5 milliseconds (with no BB in front of it) to return all the way forward from the time the nozzle solenoid is told to shut off. Pushing a BB through the bucking lips will slow the nozzle return speed down some especially if its fit is fairly tight or if you are using heavier ammo. If the dr is lower than 12 the poppet valve will fire off before the BB is seated properly and the nozzle has made a good seal with the bucking. This will result in an air leak and a loss of power, consistency and accuracy or jamming especially in full auto. If you are not trying to achieve a high rate of fire the dr should be set high to allow the maximum amount of time for the BB to settle and the air nozzle to seal. Letís say 17 for the dr.

With the dwells we have set we can now add them together: dn 10; dP 4.5; rF 4; dr 17 for a total of 35.5 milliseconds per cycle. Since 1 second is 1000 milliseconds we can take 1000 and divide it by the total in this case 35.5 giving us 28.17 rounds per second. If you would like to shoot a specific rps you can divide 1000 by that number and that will help figure out what the rF and dr settings need to be. You have already established the lowest you can go with the dn and dP so those are basically fixed. For example 18 rps would be 1000/18=55.5, 55.5-dn10-dP4.5=41, 41 can now be spread between rF and dr. Letís say rF 12 and dr 29. This will give you very close to 18 rps.

If your gun just doesn't shoot how you think it should, one or more of the FCU settings may be the cause. Making changes to the FCU can be a little disconcerting if you donít really understand what the adjustments do are how they really affect the systems performance. This long winded explanation should shed some light on the mysteries of the FCU but just remember that nothing you do in the FCU will actually damage the engine. If any changes made seem to make the Fusion Engine no longer function properly, the changes can always be undone or reset to default.

This was originally posted on by Cyclops
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Old 04-04-2018, 10:48 PM
Airaid33 Airaid33 is offline
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nice info on how to tune a Polarstar
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