Semi-auto seizures (VFC SCAR-L CQC)

Discussion in 'Gun Building, Modifications & Repairs' started by nectricks, May 3, 2016.

  1. nectricks

    nectricks New Member

    Hello, guys! :D
    The weapon with the semi-auto seizure is a VFC SCAR-L CQC. It shoots at ~415 fps (0.20 g).
    The battery is a LiFePO4 9.9v 15C 1000 mAh.
    The problem occurs whenever I pull the trigger repeatedly and rapidly (even if on complete yet rapid pulls).

    Additional info:
    The gun, which used to drain batteries right on the first day of gaming, remained "down for maintenance" for some time and then I found it was a loose motor connector. When I restored the battery, which I thought to be the faulty part as it had one completely-drained cell, I noticed my AEG was a bit slow trigger response-wise, even with other LiFes and 7.4v LiPos.
    The weird thing is that in my last game, some days ago, it wasn't locking that easy anymore on rapid semi-auto. The RoF has always been slow, but I THINK that's normal for its stock motor and that battery (is that?).

    Interesting weather notes:
    a) some games ago, a friend noticed its pistol grip was somewhat hot after we checked its semi-auto for some time (he was wearing Mechanix Originals);
    b) the day the AEG worked "properly" (as mentioned in the previous bold text ^) was colder than usually, yet being hot for some (~20ºC / ~68ºF) - (video right below).

    * YouTube link with the AEG firing on semi-auto and full-auto - TURN ON ANNOTATIONS *
    Of course I want to avoid opening the mechbox for no reason and possibly messing something up, thus I'm asking for help; any insight for troubleshooting is welcome.
    Possible reasons for the issue:
    1. stock wiring set and regular mini-Tamiya plugs. Should 16 awg properly fit in its gearbox? Else, is 18 awg ok? If changing plugs, I'll opt for Deans, don't you worry haha;
    2. insufficient power. Not sure if the "half-cycle" shown in the video is caused by that. But if the LiFe can't handle it properly, what could (with NO harm)?! :'(
    3. auto-shimming gears. Makes sense? If so, in order to shim my mechbox, would I need to change its gears or just the shimming set? Because gears are expensive here in Brazil (as I believe you wouldn't recommend random gears, but good ones);
    4. faulty/weak motor. I'll just throw in ZCI 22 TPA in it if that's A MUST for this moment, as the currency is terrible now;
    5. motor height adjustment. Not sure if the whining sound (video above ^) is due either to item 4 or 5, or if that's normal for VFC;
    6. faulty/weary piston. Does that make sense?

    Thank you so much; I'm sorry for the long post.
    Last edited: May 4, 2016
  2. kazuma5201

    kazuma5201 New Member

    1. 18 gauge wiring is not acceptable on any occasion. 16(should be the standard for stock aeg) or 14 is what you want, stranded copper wire. Tamiya plugs are fine, but if you get them all to at least a Deans you may notice slightly quicker response from the trigger.

    2. "Max continuous discharge rate - 15C " is part of your problem. For all I know, it could be pushing 10C consistently, maxing at 15 here and there. That's super duper low imo. Find one that is 20 or 25c and that should take care of your issue. Get an 11.1v as it won't hurt anything. You should get a mosfet regardless at some point to at least protect your trigger contacts as those will corrode/blacken over time. As far as the mAh, do what you need to do; whatever fits and accommodates the time frame you want it to last.

    3. If you have auto-shimming gears, those should actually be alright as long as it isn't a high fps setup. If it's stock, you may be okay. You can still shim them if you want, but this does require opening the gearbox and adding shims until they're spinning freely but aligned with one another properly, and to the point that there is no wiggle room afterwards for them.

    4. It's entirely possible the stock motor wasn't one that great, and it's slowly dying. I don't know for sure, but if you have a spare motor, try that. Make sure to only perform ONE CHANGE at a time, then write down the results. Keep in mind the motor only uses what it can handle from the battery, so an 11.1v won't hurt it unless your wiring is funky/improper.

    5. If it's not lining up correctly with the bevel, then yes this could cause your motor to struggle, which in turn will heat the motor AND battery due to the strain. This generally refers to things being too tight together between that first gear and the pinion gear on the motor - either the motor is too far up or the gear is too tightly shimmed against it.

    6. Piston wouldn't be causing any of this to my knowledge. It's just a piece that gets pulled back and forth with little resistance. Now if you changed out the spring to a stronger one recently, that could be part of it. That means even more resistance that the battery, motor, and gears have to work against.

  3. nectricks

    nectricks New Member

    Kazuma, thanks for the kind reply!

    Item 2: the problem is MOSFETs can't fit at all in its stock; I'd need to run the battery externally, and I must say I'll get a bit concerned under rain.

    As for the item 3: but I would then need a ton of shims (per gear) to do the work, in order to replace the gap the spring used to occupy, correct?

    Also, I forgot to mention: it's chronoing 410~417 fps (0.20 g). I'll add this info.
  4. kazuma5201

    kazuma5201 New Member

    Not a problem! Just trying to help as much as I can.

    2. I don't recommend running the battery externally if you can help it. Personally I rewired my entire gun from front to rear with some copper stranded 14 gauge from lowers, and of course the proper connectors and soldering involved. Turned out great and both my burst control and standard mosfet fit. My mostfet is actually resting(with extra wire) in the handguard while my burst control resides in the stock with my lipo. I too have a crane stock, but I actually cut the buffer tube down to leaving the second notch in place, and hollowed out the inside of the stock without doing any serious structural weakening.

    3. Ton of shims? You shouldn't. You should only need enough to mesh them up accordingly, basically only a small baggy of steel shims. If you're referring to the Spur gear where it has the very long column, just remove the metal sleeve from the previous spur gear or keep that one and add shims to it. What does it look like?
    Last edited: May 4, 2016
  5. nectricks

    nectricks New Member

    UPDATE: last night I tested my AEG with a 11.1v 20C 1100 maH and it's a completely new AEG compared to when I use it with LiFe. Way better trigger response, no semi-auto locks and better RoF.

    I've read VFC's tend to work that way indeed. Is that due to its inefficient motor?

    If so, getting this ZCI should fix the problem "forever", instead of the AEG only working with LiPo 11.1, correct?
    I'd like to avoid using MOSFET, if possible. And it would cost almost as much as the ZCI.