G&G SG553 (SIG) Mosfet Upgrade Problem

[Pfeil]

I have a new G&G SG553 (SIG series) AEG. The gun is stock with an M100 spring and chronos at 365 fps with a 7.4V LiPO. No feeding or performance issues.

My goal was to improve the trigger response and protect the trigger contacts by installing a simple Jefftron Micro Mosfet and adding a higher torque motor with neodymium magnets to replace the stock G&G one (weak magnets).

After successfully installing the mosfet, the gun fires perfectly with improved trigger response. HOWEVER, it always dry fires the first round after a new magazine is inserted. The nozzle does not cycle to its correct position after firing and is partially visible in the feed tube (3 mm). I assume it is cycling too far and moving forward into the next firing cycle. The nozzle moves forward and then back after firing, so it does not feed a BB on the first shot. I did NOT open the gearbox for the upgrade and the gun is properly reassembled.

This happens with the mosfet installed (with the original or upgraded motor) and also WITHOUT the mosfet installed and just the upgraded motor installed. Removing the mosfet and using the stock motor solves the problem.

I have also tried a hardwired Burst Wizard King Kong 2, which supposedly has some form of active braking, but the gun still does not fire the first round after inserting a new magazine.

Is there anyway to solve this issue so that I can use a mosfet and the new motor for improved trigger response? My field limit is 350 fps so I cannot install a stronger spring.

Thank you all for your feedback!

Pfeil

[ThunderCactus]

V3 has the wiring on the outside, so I'm guessing you didn't HAVE to open the mechbox to hardwire in the mosfet?

Sounds like a typical overcycle problem due to a slow cutoff lever.
What motor did you buy?

[Styrak]

Kind of related, how did you go about installing a mosfet with the upper/lower wireless contact system?

[Pfeil]

Originally Posted by ThunderCactus

V3 has the wiring on the outside, so I'm guessing you didn't HAVE to open the mechbox to hardwire in the mosfet?

Sounds like a typical overcycle problem due to a slow cutoff lever.
What motor did you buy?

Hi

Correct, there was no need to open the mechbox. The motor is a Tornado F1 High Torque Gen 2 (Short) made by GunFire.

Is there anything I can do about the cutoff lever?

[Pfeil]

Originally Posted by Styrak

Kind of related, how did you go about installing a mosfet with the upper/lower wireless contact system?

It was a challenge due to the limited space! Basically, the mosfet only has one integrated signal (trigger wire), so there is one less wire to run.

1) Mosfet sits in hand guard near the back under the barrel (before the stock fuse).

2) You have to run the signal wire (blue) to the bottom trigger contact. This is done by carefully pushing it through the slot where the positive and negative wires exit the top receiver (barrel). I.e. insert it from the hand guard towards the back. I had to remove the barrel (single large Phillips-head screw in mag well) to get this cable to enter the hop area. Smaller cables will enter without removing the barrel. Pull the cable out as far as you can so you have slack (mine was 0.5 m long).

3) Unsolder the positive wire that runs from the motor to the bottom contact on the trigger. Take pictures beforehand so you can route your wires correctly later.

4) Solder a new positive wire to the top of the positive contact on the lower receiver - above the second positive wire that runs to the trigger contact. This wire must run to the front of the mechbox and then wrap around it and then run along the right side of the mechbox back to the motor. See photo. This is the most challenging part: getting the new wire soldered without unsoldering the other one below it.

5) Solder the blue wire to this trigger contact as shown in the photo. Run the wire as shown.

6) Run the wires as shown. When reassembling, join the upper and lower receivers while gently pulling the excess blue signal wire back out into the hand guard. The wire will run below the hop unit, crossing in front of it. Be careful not to pinch it when closing the upper and lower receivers.

Once finished, simply retain the excess length of the blue cable by bundling it carefully (I taped mine with electrical tape) out of the way in the hand guard. When you want to disassemble the gun, simply undo the blue signal wire bundle (remove the tape), separate the upper and lower a little and then pull the wire back into the upper as you separate the two parts of the receiver. They are still attached by the blue wire, but there is enough excess wire with 0.5 m to work on the two halves or you can unsolder the blue wire easily enough to fully separate them.

-> Note that you are retaining the second, short, positive wire that runs from the trigger to the contact on the lower receiver. This is your second trigger or signal wire that needs to be run to the positive wire.

It works perfectly. (Except the overcycling in my case).

[ThunderCactus]

interesting that it occurs with the mosfet and original motor....
If active braking didn't cause it to stop at the proper spot, it's definitely not getting the signal to stop early enough.
Open the mechbox, make sure the cutoff lever moves freely, you might have to put a stronger spring on it to get it to disengage the trigger faster.

[Pfeil]

Originally Posted by ThunderCactus

interesting that it occurs with the mosfet and original motor....
If active braking didn't cause it to stop at the proper spot, it's definitely not getting the signal to stop early enough.
Open the mechbox, make sure the ARL moves freely, you might have to put a stronger spring on it to get it to disengage the trigger faster.

Thank you for your help ThunderCactus.

It is strange that it occurs with the mosfet and original motor. You would think that the electrical circuit would simply be more efficient than the stock one. It's as if the mosfet were taking too long to cut the power. I thought it might be the trigger but can't see why it would work correctly without the mosfet.

Should I try a stronger spring on the ARL or on the cutoff lever? Or perhaps both?

[ThunderCactus]

meant cutoff lever, not ARL, dunno why i typed ARL...

[Pfeil]

Just a quick update. I was finally able to get hold of a GATE PicoAAB Mosfet with active braking to try in the SIG 553 (SG553). It seems to have solved the problem with the dry firing of the first round after changing magazines.

The gun is extremely sensitive to any change in the electrical circuit. Before installing the PicoAAB, I removed the factory fuse which resulted in the same symptom even with a 7,4V LIPO. Although I have not opened the gearbox, it is clear that the CUT OFF lever has lateral play. I did replace the cut off lever spring for a harder one (SHS) as well.

Installing a MOSFET in this gun is not for the faint of heart. Space constraints both in the hand guard and the lower receiver as well the unique split contacts for the upper and lower receivers, makes adding and routing a continuous cable to the motor along with the signal wires a challenge. It can be done, but there is a great deal of cursing while trying to coax everything back together while holding the complex selector switch gears as well.

Size-wise, I would recommend something smaller than the Gate PicoAAB. Yes, it is small, but the factory connectors (blades) and very short leads are annoying, occupy more space than necessary and make the installation more difficult than it needs to be all while adding more connections (and resistance). The Jefftron Micro Mosfet fits very well but because of the dry firing (probable over spinning) was not an option on my sample.

As an aside, it would appear that active braking on the Burst Wizard King Kong 2 (hardwired) doesn't work as it should because it did not remedy the problem like the GATE PicoAAB did.

[ThunderCactus]

If you're having an issue with a NON braking FET overspinning the gearbox, the issue isn't the fact it doesn't have AB, the issue is the motor magnets are too weak. You can eliminate the need for AB by just using a neo magnet motor

[Pfeil]

Originally Posted by ThunderCactus

If you're having an issue with a NON braking FET overspinning the gearbox, the issue isn't the fact it doesn't have AB, the issue is the motor magnets are too weak. You can eliminate the need for AB by just using a neo magnet motor

Hi,

Unfortunately, that didn't work in this case either. Simply replacing the stock motor with a neo magnet motor (no mosfet, same LIPO) actually resulted in the same issue. The only way it would not dry fire the first round was to leave everything stock. Changing the motor or just adding the mosfet consistently caused the same issue. Even trying a non-braking mosfet with the neo motor wouldn't solve it.

When I get around to opening the gearbox, I'll probably try adding a tappet plate delayer, replace the cutoff lever/eliminate the lateral play, and check the trigger assembly/spring as well.

For now though, the PicoAAB (braking mosfet) seems to eliminate the symptom at least.

[ThunderCactus]

The only way you'd overspin a gearbox on a neo magnet motor is if the cutoff lever wasn't working properly, so that's definitely your issue right there.
Using big heavy ass 26:1 gears or high speed 10:1 gears, a neo magnet motor will stop both dead in their tracks on an 11.1