The "joys" (aka. trials) of being a gun doctor!

[lurkingknight]

is this a new CA 249 or one that's been sitting for a while?




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edit:

On a somewhat related note to the mosfet comments previously about trigger contact pins falling out... While a mosfet can't prevent components from shitty manufacture coming apart... they can prevent this:


The gun is a CA g36 running on a CA red motor, seems to be a stock gearset, shimmed reasonably well, shooting about 380-390. This gun is a teammate's gun. He doesn't play that often, only when we do private club games with our family and friends and when we gather to do nightfall. This gun was used as a support gun, firing full auto. Previous to NF3, it was used in NF2 and again in a game in the fall. So not a huge number of rounds through it.

No mosfet, was fused until beginning of NF3 when we discovered the fuse was ... well fused. (Thanks to the guys at I think niagara quartermaster for the crimp terminal) We were able to put it back together and run it for NF3.

Owner gave it over to me to rewire in the off season to get rid of the crimp connector. It looked like a stock wiring harness in silver wire, it wasn't crappy wire, but it wasn't awesome wire, but the harness itself was good, no melted points no nothing, so even mediocre wiring can hold up to what I'm about to show.

We powered this gun with a fairly large 7.4 lipo, something like a 50C 2300mah brick rear wired in a KV stock. The intent was to have enough power to drive the motor without danger of overdrawing the battery, on top of having a good mah reserve so the battery would last a while into the game as a support gun. Low internal resistance of the battery would mean it won't heat up as much when under constant or extreme load.


So fastfoward to this weekend, I decided I had time to open it up to rewire it in milspec alpha wire. Only to discover that the screw holding one of the contacts in place would not budge. It stripped and resisted all attempts to be undone.

Then I looked at the contacts.




lol. Initially I saw the 1 tab sitting much lower than the other one.

WAT.

Looking closer, you see the base of the fins at the housing is melted as well.

So I cut off the whole thing and put in a new housing and contacts into the gun and away it went.

Further autopsy on the contacts



Looks alright from here, aside from the screw that wouldn't budge.



Cutting the plastic from around the screw I grabbed it with my vice grips and got it out.



Looking back inside the contacts to where the screw would have come out from. Basically the power arced from the near tab across the other contact and AGAIN through the screw. Path of least resistance to the main wire. The screw was melted into place.



In addition to arcing through the contact, you can see it arced completely along the length of the contacts, shortest path being the gap between the 2 plates at the housing, where it melted. All the carbon buildup is on the base of the tabs, away from where the shuttle was in full contact. On the backside of the tab that arced to the screw was also black, it was burned on both sides.



The housing split open so you can see the amount of damage to the spot where the screw sits through the contacts.



A mosfet would have 100% prevented this. Had this gun continued being used when this damage initially occured, it's possible the contacts would've melted through the nylon completely and merged the 2 contacts together creating a runaway. Worst case was that the gearbox shell itself could've electrified and arced, causing more damage to the shell itself or possibly injury, as your finger is on a big metal trigger very close to this action.

[Spike]

I think it's an older one, got it used in the classifieds. It's rock solid, but the gear was meh. All SHS parts in it now, though.

MOSFETS IN EVERYTHING FOREVER BECAUSE WHY NOT?

[Styrak]

Hunh? Was there supposed to be a picture?

[Styrak]

Dat shimming

[lurkingknight]

[Red Dot]

Poor pistons, they never saw it coming...

[br0k3nsa1nt]

My biggest pet peeve is gasket seal in mags. I got a second hand 1911 and all of the mags had gasket seal. I had to scrape it all off with an exacto knife. Lubed the o-rings and no issues.

It the leak persists, I like using SAP(it stands for something, but I forget) tape. It's a super stretchy rubber tape used in electrical work. It sticks best to itself and when crushed in somewhere it acts as a great seal that can be removed just by slicing and peeling it off.


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[IrishR01]

A couple months ago I was working on this local kids Lucid AK-47 because of "really low fps" as he described it. One of those Buyairsoft clear-soft guns of course.

Took it all apart and it seemed to be a normal V3 gearbox, and of 'alright' build quality. Now, I stripped the whole gearbox down and looked through the cylinder because there was a A LOT of this... goopy liquid coming out. I figured it was just a lot of factory lube, but I was incorrect.

There were at least 3 or 4 dead ants and a very large queen(?) ant inside the cylinder head where the nozzle would go and around the cylinder itself. I'm actually surprised they didn't just fly out the barrel with every shot, but the combination of lube and this goop must have kept them in place the whole time. This kid just leaves his airsoft guns laying around outside from what I've been told by his parents.

Cleaned the gearbox out, lubed it back up and the gun shot just fine for a Lucid gun (280 fps or so).

Just a side-note, TM (and others of that style) V3 gearboxes with the fuse that fits down near the hop-up DO NOT work in Lucid AKs. They seem to come stock with a fuse that sits not in the receiver itself but in the stock, attached with large tamiya connectors instead of the standard small ones.
Really, don't even bother with Lucid if you know what's good for you.

[RainyEyes]

SO recently I've acquired a boneyard APS UAR and trying to preserve APS' reputation for quality workmanship, I present to you how two people decided to fix this gun!

The bullpup design means that it is like a P90 with a trigger bar to reach the gearbox housed in the stock. And when I say housed i mean it's held on by 1 little hex screw.

FIRSTLY: Trigger bar was missing so this was the fix!
Microswitch (the kind on computer mouses) wired directly to the motor! Do engage by the gearbox and do not pass Go!

Me being the genius I am, I used hot glue to shim the trigger so that it now has a hair trigger since the metal arm that engages the microswitch. This switch was installed by drilling a hole into the lower receiver and putting in a stainless steel screw that's simply held on by retention. It's stupid but it works.



Do you want broken gear teeths? Then use ball-bearing bushings! Almost guaranteed to explode and mess up your whole gearbox, leaving permanent scratches in your gearbox and gears!



Broken shiny tooth:



After replacing the bearings with solid metal bushings, I got it up and running again.

More pics to come if I get a chance.