Double Eagle M906C - Internal upgrades / tinkering

[Colin Allen]

22 hours ago, Herrgh said:

 

I used long thin metal files which meant I could only tackle the job from certain angles. This resulted, try as I might to avoid it, in other parts of the gearbox in line with the file also getting a very light sanding, but this shouldn't really effect anything. 

I sometimes use a hammer and small chisel to remove them.

[RostokMcSpoons]

Hi guys, been a while since I've been around these parts... A combination of being skint through trying out a lower-paid job (in a much better one now thankfully), knackered knees and ankles, and worst of all a bad case of tinnitus caused by a grenade going off right next to me in a very confined doorway in the last game i played... meant I've not played for months. 

Luckily the tinnitus has eased off back to where it used to be, so as long a as i wear ear-pro i will try again.

 

Anyway, glad to see the thread is being useful still!

 

My beloved m906c has also decided to do something bad to the Falcon ETU again.  I think the damned things are very heat sensitive, so a poorly shimmed gearbox or a badly adjusted motor, or just a lot of single shot spamming can cause it to fail.  

So these updates are good info 👍

 

My alternative thought is to go for one of those drop in hpa engines ... I'll wait until someone beats me to it so i can crib from their experience 😋

Edited May 10 by RostokMcSpoons

[Herrgh]

Hello gang,

 

Solink 35k motor arrived yesterday, which I immediately slotted into my M906C. A superlative improvement over the stock motor - the gun is now very snappy, very responsive, a semi-auto spamming machine. So me happy. 

 

However, I have a slight conundrum now.

 

On semi, FPS hovered around 265 on 0.25g.

On auto, FPS hovered around 300 on 0.25g.

 

(All this with no precocking or active braking - the only setting I've touched is the Perun's ROF reduction, maxed out) 

 

Huh.

 

Adding 2 steps of active brake on Semi mode via the Perun, has now brought the semi FPS up to 300, same as auto. I am at a loss as to what is going on.

 

I think there must be a little bit of overspin or something? Is the piston coming to rest after each semi shot some place in the cylinder that is robbing it of air volume?

 

Edit: and why only on semi? My googling suggests usually it's the other way round (auto has lower fps) I think due to premature engagement? 

Edited May 16 by Herrgh
clarification

[Adolf Hamster]

1 hour ago, Herrgh said:

Edit: and why only on semi? My googling suggests usually it's the other way round (auto has lower fps) I think due to premature engagement? 

 

you are correct the stereotypical symptom is higher energy on semi, with pme skipping teeth and resulting in the piston not being drawn back fully giving a lower energy in auto after the motor has spooled up.

 

the other way around is a tad more mysterious, and especially that it can be cured with a different precock setting.

 

the only thing i can think is that at your initial 2 steps of precocking, the tappet plate hasn't been fully released, meaning the order of operations is tappet plate releases then fire, with the snappy brushless able to wind the piston back and release before the tappet has had time to get fully into battery. with more precocking it's stopping after the tappet release meaning it's in battery and all the motor is doing is winding the piston back a little before it sends.

 

but if that were the case, you'd expect the lower fps to also occurr in auto, as i doubt the motor from a standing start is going to be faster from tappet release to piston release than the same motor already wound up to full chat.

 

1 hour ago, Herrgh said:

I think there must be a little bit of overspin or something? Is the piston coming to rest after each semi shot some place in the cylinder that is robbing it of air volume?

 

it's worth noting that precock is just controlling the amount of overspin, and in terms of air volume a fully precocked piston has more time to fill itself with air than it will under full auto conditions, so you'd also expect it to give more energy than auto if the cylinder refill time was a factor.

 

 

[Herrgh]

6 hours ago, Adolf Hamster said:

the only thing i can think is that at your initial 2 steps of precocking

 

My bad, I've actually set SEMI to have just 1 (not 2) step of Active Braking. Precocking (I think) tries to get the spring to stop at the rearmost position ready for the next shot but I have not turned that on in any way for either SEMI or AUTO. At the moment the gun is set up thusly:

SEMI

Active Braking - Level 1

Precocking - Off

ROF Reduction - None

 

AUTO

Active Braking - Off

Precocking - Off

ROF Reduction - Level 5

 

I've just tested adding some ROF reduction to SEMI, just in case that was the common denominator, but obviously that has had no effect on FPS in that mode. I've shot off an email to Perun in case they have any insight into this weird problem, but I'd still like to know what the underlying issue is (even though thanks to the Perun it's no longer an issue).

[Herrgh]

Disregard everything I broke it 

[Herrgh]

Disassembled the whole thing - turns out:

• The piston head has detached from the piston. No damage. This is probably cos I didn't use threadlock.
• The nozzle lips that let it sit in the tappet plate have broken along one cardinal edge, but I have an XT POM-based replacement that I wanted to use anyway, so I will install that.

Will put it back together better than I did before and give an FPS report once it's done.

[Adolf Hamster]

23 hours ago, Herrgh said:

My bad, I've actually set SEMI to have just 1 (not 2) step of Active Braking. Precocking (I think) tries to get the spring to stop at the rearmost position ready for the next shot but I have not turned that on in any way for either SEMI or AUTO. At the moment the gun is set up thusly:

 

Active brake on its own is supposed to prevent overspin, which could be thought of like a natural pre-cock, but can often have the unintended effect of stopping the box too soon giving trigger lockups as the cutoff timing does take into account a little bit of overspin.

 

Typically i tend to reccommend using ab and precocking together or not at all, although it could be argued a precock setting without ab probably wont harm anything.

 

Ofc none of that has anything to do with the energy output, but i see you've got to the bottom of that mystery.

[Herrgh]

Hello again!

 

I finally got round to fixing my gun and it seems to be operating okay. Piston head is now thread locked in. I feel that there is a slight springy "twang" to the end of each shot, but not sure what I can do about that without breaking it open again; I want to get at least one game day under my belt with this thing before messing around with it more. 

 

Anyhoo, the FPS has now gone up by around 20(!), which I attribute to the new XT POM nozzle with o-ring just giving overall a better air-seal.

 

However, the gun is still exhibiting the odd effect of having a higher FPS on auto compared to semi. Applying one step of active breaking to the semi-mode brings the semi FPS up to that of full auto.

 

Here are the chrono results for my last 24 shots (with 0.25g ammo):

 

 

SEMI

317.2

320.4

310.7

322.1

316.9

311

319.5 

311

311.5

317.4

310.7

302.9

320.7

322.3

 

FULL AUTO

311.4

320.5

317.9

320.7

315.9

309.8

309

313.6

317.6

319.2

308.6

 

MIN - 302.9

MAX - 322.3

AVG - 315.1

 

Attached is a the above expressed in a line chart. Copilot says my hardest shot comes out to 1.21 joules on 0.25g (this is using an M105 spring). I'll look to stepping down to a M100, as I really didn't expect that switching out the nozzle to one with a o-ring would "improve" things that much. The joule-age is a tad too high for me to be comfortable. 

 

Anyways, I think there is definitely some weird cycling issue here, but I can't really figure out why, or what is causing it. It's interesting that the gun appears to repeatedly peak at around 320 FPS before dropping back down to ~310FPS. Again, turning OFF all active braking will drop my shots to approx 290fps on semi (unchanged on full auto). Does anyone have any insight? 

 

(I have a video showing the pistol cycling which I'll try to link to soon, to help with diagnosing.) 

[mightyjebus]

it might be a red herring. Have you tried a different chrono as the chrono you are using might not be the best for accurate FPS readings in full auto.

[Adolf Hamster]

Those numbers look pretty similar to me? If anything auto tends to be more often in the sub 310 range than semi.

 

Spring twang can sometimes be resolved with precocking, getting the spring immediately under tension after the previous shot, although that comes with the unfortunate downside of also making the gun feel more responsive.....

[Herrgh]

More data (as I realised the data set above doesn't show the point I was trying to make, that semi is low FPS until I add 1 step of Active Brake, which brings it in line with the FPS shown on auto). 

 

SEMI No AB, SEMI ABx1, and AUTO were recorded using a Solink brushless motor.

The "Chaoli" lines are the same, but using the M906Cs stock (crap) motor.

 

 

Motor is definitely responsible for this behaviour. Must be some sort of overspin or something, but I've definitely lost the magical sparkle that the DE factory put in the gearbox that allowed the stock setup to be quite stable in its FPS (around 290FPS on 0.25g), instead of the wild variances shown here. 

 

Precocking level 1 on semi (w/ solink motor) results in a slight drop in power from the levels for SEMI No AB. (Perun advise that AB and PC can't be on at the same time). 

 

Precocking level 5 on semi results in a doubleshot.

 

My chronometer is an AceTech AC6000BT. It was a bit expensive so hopefully there are no issues with its accuracy! 

Edited June 24 by Herrgh

[pyromancer6]

My dremel comes tomorrow so this thread's going to be invaluable in getting the perun fitted all sound. Very excited to get my DE UTR-45 back up and running! (although trying helical gears for the first time is going to be an absolute nightmare!)

[Fatboy40]

8 hours ago, pyromancer6 said:

My dremel comes tomorrow so this thread's going to be invaluable in getting the perun fitted all sound.

 

I may have missed a post in this thread but why would you need to remove any material from the standard gearbox shell of a DE M900 to fit a Perun V2 Hybrid?

 

They're as basic as they come and for example a GATE Titan II juts drops straight in, no modification required, so a Perun V2 Hybrid should be just the same (personally I go with GATE controller as I prefer an optical trigger).

[pyromancer6]

10 hours ago, Fatboy40 said:

 

I may have missed a post in this thread but why would you need to remove any material from the standard gearbox shell of a DE M900 to fit a Perun V2 Hybrid?

 

They're as basic as they come and for example a GATE Titan II juts drops straight in, no modification required, so a Perun V2 Hybrid should be just the same (personally I go with GATE controller as I prefer an optical trigger).

The DE mosfet is a very similar dual board design similar to a GATE Titan so they drop right in. Unfortunately, the Perun gets stuck on a little nub on the left-shell of the gearbox which requires a bit of fitment work.

See Herrgh's posts:
 

On 20/04/2025 at 20:30, Herrgh said:

I've already run into my first problem:

The Perun won't sit flat against the side of the gearbox case because of the "bump" circled below.

The Perun magnet holder that is affixed to the trigger is making contact with the horizontal post indicated with the arrow.

 

 

As far as I can tell the "bump" doesn't appear to do anything. I'll have to file these down to make everything fit. What tool do I need to obtain to do this?

  

On 21/04/2025 at 19:01, Herrgh said:

Yes, apologies, I misread the instructions as saying that the magnet holder shouldn't be in contact with that post (it should!)

 

I don't have a dremel to hand but some hand files have done the trick.

 

Have done the sensor tests and it's all working! Now to reassemble it without too much cursing (ambi controls and working ambi bolt catches make for a poor first timer attempt at this sort of thing...) 

Dremel arrived just earlier. It's going to be a very painful couple of days (not helped by the fact I've got a fracture in my wrist!)

UPDATE: Will be tomorrow instead - turns out the set of 15 accessories didn't include a metal die-grinder small enough to get at the peg without blasting half the gearbox. Did end up using the dremel to make my selector fit and able to move with the EZO bearings however. Overshimmed the shit out of it so they were as pushed out as they're ever going to be & took off enough until it selected smooth, job's a gooden.

Edited Wednesday at 20:41 by pyromancer6