Semi-Auto Seizure Explained ( trigger glitch )
 

Explanation for semi-auto seizing

Semi-auto seizing occurs during an incomplete trigger pull. Incomplete trigger pulls is prone when the shooter taps on the trigger or pulls the trigger half way just enough for the trigger switch to connect and fire the gun. Half way trigger pulls are usually done to imitate poor real steel firing techniques where the shooter pulls slowly -- waiting for the sear to disengage -- and releases the trigger immediately after the weapon is cycled. Since AEGs don't have sears, trigger pulls should be quick (to avoid trigger switch oxidation) and complete (to avoid gearbox seizures). The range of trigger movement should be FULL. (A rule of thumb is to pull the trigger all the way back on every shot.)


When the trigger is pulled just enough for the trigger switch to connect, the gun will either half crank the piston, or it will cycle and release the piston to fire a shot. After the piston has been released to fire a shot, the sector gear continues to rotate. Underneath the sector gear is the disconnector cam. While the sector gear is still rotating, the sector gear disconnector cam rotates along and pushes down on the cut-off lever. The cut-off lever rotates 20 degrees (counter-clockwise) along it's pivoting axis and pushes up on the trigger switch block. When the trigger switch block is pushed up, it separates from the trigger bent. The trigger bent is located directly on the trigger itself. The trigger switch return spring then pulls back on the trigger switch block and opens the entire electrical system causing the gun to stop firing. This process is normal such that the gun will only fire one shot during semi-auto.


However, since the trigger pull is done ever so slightly, not enough power is available to further cycle the sector gear. The sector gear will remain at it's position where the sector gear disconnector cam continues to push down on the cut-off lever. The cut-off lever will be locked in the 20 degrees position. At this point, every time you pull the trigger, the trigger switch block will ride up the cut-off lever like a ramp. The trigger switch return spring will pull the trigger switch block rearwards before the switch can connect and complete the electrical circuit to fire another shot. When the gearbox is seized, the clicking sound you hear is the trigger switch block being pulled back and smacking against the trigger return stop (trigger return stop: a protruding piece that's directly molded onto the gearbox. Faulty gearboxes will eventually have this small part broken due to repeated hits by the trigger switch block.)


To fix this problem, the user changes to full auto, fires a round, and returns back to semi. This works because during full auto, the cut-off switch is no longer engaged with the sector gear disconnector cam. The cut-off switch is rotated pass 20 degrees to 45 degrees. At 45 degrees, the cut-off switch is raised above the trigger switch block and can no longer knock out the electrical system.


Manchovie mentioned about using a larger battery to prevent semi-auto seizing. It's true because when excess amount of volts is used, the sector gear disconnector cam will almost always have enough power to rotate completely and not get stuck at a position where it continues to push down on the cut-off lever. So even if you slightly tap on the trigger, enough electricity will cause the sector gear to completely rotate.

end

If Greylocks was a mod, this is thread he wouldn't delete. Very nice work.

Well done Raygis.

(On a side note, I dare someone to try and make a CA33E seize up. :wink: )

So, if a G&P SPR with a 150SP spring and 9.6V 3300mAh battery, that is prone to seizing up in the way you describe, and the trigger is pulled full back each & every time, how is it that it still seizes every couple dozen shots?

I've worked on one, was told by the owner that the problem is only pulling the trigger halfway at times, and/or til it fires, then releasing it. My answer was to pull it every time full through. Yet after I fixed a bad install of a Carrot grip, I was putting it through it's paces and found that even when pulling full clean trigger pulls all the way back, it'd still lock up once in a while and have to go to a full burst to fix it. Is it still normal for a mechbox to lock up when shot properly? My MP5 never locks up when fired repeatedly on semi, nor have I experieced any others doing that until the SPR came around.

Every Ver III gun I've owned does it (alot of guns). As their switch is different from a Ver II and the location of switch stop points will also be different, it stands to reason that this may be a "bug" that you just have to live with for Ver III guns.

The SPR uses a different switch and different mechbox from any MP5. Subtle differences in positioning of pieces can make all the difference here.

Since I don't have your gun with me to examine, my best guess is this:

The source to your problem is explained on paragraph 3 where the sector gear disconnector cam continues to push down on the cut-off lever because not enough power is available to further cycle the sector gear.

The solution is in paragraph 5...

In your case, I'd change the wiring and battery plugs to those that are more energy efficient. Go for Deans battery plugs. If that doesn't work, the combo of a large 10.8V battery pack and Deans will definetly solve your problem.

i had this problem with my MP7 and although this youtube video is kind of amateur this is what helped me figure out what was being said in the OP so i figured i would post it to help anyone else having this problem

the part you need to see with the explanation is at 8:30 into the vid (part 1) and he describes how to correctly position the sector gear and check when reassembling.
seeing this with the description made it all click for me so if youre having this problem hopefully this clarifies it for you too!

YouTube - Tokyo Marui MP7A1 Gearbox Part 1

what if switching the selector doesnt work?
Brand new Tm m733 with stock battery

Then it's a different issue, poor contacts, motor wires loose, or something else.

As for stalker, every pull of the trigger is a differently timed cycle.
Not to get too technical, but as stuff heats up, electrical resistance in the system rises as well, meaning less voltage. Not an audible difference, but enough that it would causes the sector gear to stop a few teeth early, and possibly right on the cutoff lever.
Not to mention the motors we use are FAR from perfect lol
The best solution I've seen to this issue so far is an SW-COMP with active braking. Then as long as your making full and complete trigger pulls in semi, your piston is ALWAYS stopping at it's ideal rest point (IE the point where you don't need to hit the anti-reversal when disassembling the mechbox)

The only other thing you need to watch out for is what Amos and I refer to as 'cycle overlap'. Most common when running heavy, torque up gears that carry alot of momentum(prometheus), weaker springs (<350fps), motors with low magnet strength (G&P M120 or any stock motors really) and large batteries (9.6v large), which also happens to be the exact setup I had at a scrim lol
Anyway you hear it spool up from 900 to 1200rpm, then when you let go of the trigger the gun 'runs away' for 10 rounds.
Also cured by active braking SW-COMPS, but the reason I bring it up is because it too can cause stoppages when switching from full auto to semi auto in AEG's....and it's annoying lol

well i am sure it was sezure and battery..
I had pitched it, but the wife said to stop, smoke, relax and examine.
so i was examining the battery, pulled out eh DVM and figured out positive and negitive.
attached the wires and nothing, figured maybe it runs backwards. swappdthe wires hit the trigger and heard a little click, switched the wires around again and it fires fine...
where do i get one of those special anti sezure kits hahahah
TC

unconventional-airsoft.com
But you need a gundoc to install it as it requires a complete reqiring of your AEG, you may lose the ability to reliably use your AEG in the rain, and you may need to get your motor tuned down the road when you start upgrading your gun.
Unless you REALLY want 3 shot burst or LiPo batteries, it's not really worth the effort...

I dont know where everyone is going with losing the ability to use it in the rain.

If your using em in enclosed guns (ie P90, M14 etc) There isnt a problem.

On my C7, I put a large 1" diameter heat shrink tubing over the whole unit once installed (connecting wires, contacts, Mosfet etc). Im running firefox 11.1v lipos. Its been in MANY rained out games without any electrical or mechanical issues. If your STILL worried about rain, heatshrink your connectors (you will have to cut them to remove them later) and keep your dust cover closed.

MAY lose the ability to use in the rain.
My 249's TM is under the feed tray cover so it doesn't get wet, it's in a sealed AN-PEQ on my M4
But if your mounting in inside a handguard, or somewhere water can get to, it probably won't last out a rain game.
And covering it with something can be a bad idea, these things can get hot on certain setups and they need airflow to cool down, especially during excessive semi auto fire.
But you can always take the heatshrink off if you find it overheats too often!

I would like to lipos simply as i have a couple Big ones (med to big)
But i picked up a 8.4v 1400 intelect from an Buddy and MY ROF quad rupled..
IT was all battery baby, 1x G&P Mag with 100 rds and a 2$ shredded Visicolor target says its ok now :)
I think a 8.4 1600 will be Perfect, as you have said hahahah
C i hear, just dont listen.

Although a bud was going to lend me a 1600 mini 9.6 but as mentioned thats a bad idea in a all stock unshimmed rig
thanks again everyone
(God i say that alot)

Nice writeup!

This semi-auto lockup problem can be a real problem for some players when it happens to semi-only guns in the field.

For example in countries where the guns must have full-auto disabled, you can't fix it in the field by briefly switching to full-auto. If it happens to you, you're stuck! You can see how this would be a non-trivial and annoying problem to deal with in the field. In fact, this exact issue faced by players in countries like Germany, New Zealand, Australia, etc with semi-only laws is the reason I sell the Anti-Lockup Unit (aka AEG Forward Assist). It bumps the motor and gears forward just enough to get past the "dead spot" if it happens, but can't be used to fire fullauto.

Like I said, thankfully in Canada we don't have a law against fullauto so it's a product not primarily aimed at Canada. :) For us the field-expedient fix of a quick switch to fullauto is easy if the problem does hit you during play (unless your gun has fullauto mechanically disabled).