M14 DMR Mosfet advice.

[Stevo4345]

Slowly working through the G&G M14 faults and making progress, but on a test fit I managed to jam one of the motor wires between the stock and gearbox and stripped the insulation off. Decided to rewire as it was a bit of a shonky job to start with but while stripping out the wiring thought this may be a good time to add a Mosfet.

It's Primarily to protect the contacts, have already refinished them as the trigger trolley was sticking, found some pretty bad arcing damage on one contact causing a lot of friction.

I don't need a fancy warfet or titan, no point in a dmr, have been looking at a Nano AAB, should be just the ticket but as I'm new to all this wanted to check first.

Plan to convert everything to deans anyway and run it on a 7.4 LiPo.

Any thoughts?

 

[Adolf Hamster]

tbh i'd be wary about the more basic active brake mosfets, i've been running into some issues recently with swapping to a nanoaab in my aksu which caused seriously bad trigger locking on semi (which in a dmr isn't exactly ideal). i suspect the issue is all the guns i tried it in don't have a high enough speed build to justify the active brake.

i'd actually go even cheaper and look at the most basic of mosfets if all you're after is contact protection.

 

[Stevo4345]

Exactly why I asked, you'd have thought active brake for a dmr would be a good thing.

Thanks for the input, I'll keep investigating.

 

[Alimcd]

Great advice, I’ve had my M14 lock on semi frequently with a NanoHard and 7.4v so I will also try your recommendation and disable the active break.

 

[Lozart]

Exactly why I asked, you'd have thought active brake for a dmr would be a good thing.

Thanks for the input, I'll keep investigating.

Go for the Nano ASR instead, same but doesn't have active braking.

 

[Davegolf]

If you are running a DMR then active brake shouldn't be needed, with the spring being stronger the likelihood of overspin/PME is greatly reduced.

If you do get overspin/PME then you can always modify the cutoff lever to activate sooner ?

Its nice to make things work properly in the mechanical sense and avoid electrical gimmick bandaids... like new cars with "E" diffs, applies the brake, wrong, put a limited slip or torque bias diff in you cheap skate manufacturers!!

PS what spring, motor and gear combo are you running?

 

[Stevo4345]

The gear set is 16:1, motor is a G&G Hi Torque, not sure of the spring rating. It was converted to a DMR before I got it as a bone-yard non working gun. It's a pretty hefty, spring,I have an M120 in the spares box and it's stiffer that that.

I have already made some adjustments to the cut off lever/trigger trolley, there was a fair amount of slack in the system which I have minimised so that should help.

Thinking of locking up scenario I know the G&G gearbox has a de-cocking mechanism built into the selector switch which lifts the lever off the pawl, I'm assuming that could free it up?

 

[Davegolf]

Morning! Have you calculated the gear set as 16:1?

Im asking because if it's actually more like 18:1 then you could run an 11.1v battery - this will make trigger response and cycle speed way quicker, reducing the chance of lock up.

Im sure you know that lock up is just the gearbox inconveniently stopping with cutoff lever riding the gear cam.

Lock ups normally occur from pulling the trigger in quicker succession than the gearbox can cycle, good trigger discipline normally avoids this, a trigger with an obvious reset position that you can feel is great.

This is provided the gears come to a stop in the correct position, if you can spy the sector gear somehow through the gearbox case it helps to mark the teeth indicating the gears position, then you can test the cycle and watch to see where it rests and rectify if necessary ?

 

[Stevo4345]

Actually I didn't know that Davegolf but I do now! Gears are stamped 16-1 but I'll do a physical turn count and check. The M14 trigger bar system G&G has has obviously gone through some design changes. Some exploded parts views I have pored over show an additional spring in the system attached to the trigger to trolley lever.  Mine does not have either the mounting points or a spring. I'll  see if I can add one with the goal of firming up and giving me a more positive trigger pull as currently there's only the trigger compression spring trying to return everything back to reset the cycle.

 

[Davegolf]

Yeh on an AEG what you can feel through the trigger when you pull it is the click when the cutoff lever kicks the trolley out the way, and then when you release the trigger the trolley springing back.

If you can get these 2 actions feeling crisp it makes shooting feel more real/fun

 

[Stevo4345]

With the way G&G designed the trigger set up on this thing you’re lucky to feel anything, there’s a fair few non solid connections and all the slop adds up.

Just checked gearing, it’s right around 16.7 to 1 by my maths.

 

[Davegolf]

I thought so, a really nice high C 7.4v LiPo and basic mosfet will probably work great

That said the tinkerer in me would throw an 11.1 at it even though 16.7:1 and 25000 is borderline you do have a strong spring in there, you'd never get stopped on the cutoff ? and you could always get the cutoff lever to come in sooner if you had soooo much overspin that you started to PME ?

I say this because I've never personally used that motor, just going on the stats.

Some other AFUKs may have definitive experience of this motor.;

 

[Stevo4345]

Thanks for all the advice so far. I just got my 16awg wire delivered today so I think I'll get that installed, wire it a to deans, and see what happens with the cut off lever mod I've done already. TBC

 

[Stevo4345]

Well, the new 16awg silicon wire is a bit too thick to lay along the gearbox, will have to save that for Mosfet install as the signal wires are much thinner, so repaired the original wiring and tested it. 

Cut off lever working well now, but have major feed problems, both the HiCap and midcap mags were failing to feed 95% of the time. Will have to look into that.

Tried it on 7.4 25c and 30c, also 11.1 25c and 30c briefly. Bit sluggish on the 7.4's but very snappy on the 11.1's.

Gearbox sounds good so fingers crossed the reshim went ok.

Will check for rubbing patterns once it comes apart again.

At least it's keeping me occupied!

 

[Stevo4345]

Well I won't be giving up the day job anytime soon I think, can't seem to find the issue with the bb's feeding. Mags are feeding fine, dropping bb'sinto the hop up with the rifle upside down works fine, fit a mag, dry fire.

I'm getting 3 to 4 loose bb every mag disconnect so they are getting in the hop up feed tube.

Begining to wonder if it's even got the right nozzle in it, anyone know off the top of thier head what length it's meant to be? Either that or its cycling too fast to get the BB in? At a loss here...

 

[Adolf Hamster]

can you get it to fire at all?

nozzle would be a prime candidate, either that or feed lips on the hop rubber poking in a bit far and blocking the bb's.

 

[Stevo4345]

Yeah, checked the feed lips, all good, everything looks straight. Did notice the nozzle rest position changing a bit, sometimes extended, sometimes with a mm or two in the feed path. 

The lock ring for the hop up adjustment wheel actually slots into the front of the gearbox, the front of the hop up locks into a slot  on the outer barrel, no spring, so it should all line up. Will keep fettling and see if I can dig up some nozzle info to compare.

 

[Adolf Hamster]

Yeah, checked the feed lips, all good, everything looks straight. Did notice the nozzle rest position changing a bit, sometimes extended, sometimes with a mm or two in the feed path. 

The lock ring for the hop up adjustment wheel actually slots into the front of the gearbox, the front of the hop up locks into a slot  on the outer barrel, no spring, so it should all line up. Will keep fettling and see if I can dig up some nozzle info to compare.

different resting positions sounds pretty normal if you're not running fancy electrics.

does it ever settle completely back? if so can be useful to check that it's not sitting too far forward.

i learned the hard way not to be too gung ho about messing with nozzle lengths with the f2000.

 

[Davegolf]

As mentioned nozzle lengths are very fussy, most will only tolerate +/- 0.25mm difference from stock.

The best test for nozzle compatibility is to remove the tappet spring and push it all the way rearward / retracted manually, then drop a BB into the hop, should fall in easily but not have excessive room otherwise you run into double feed issues.

IMPORTANT - you now need to do the same but with the sector gear tappet chip providing the max rearward position - what I mean is you may be able to push the nozzle back further than the tappet chip can pull it back, get me?

If this is not good causes are wrong nozzle, tappet plate or sector gear normally.

If this is good then potentially you may need a delay chip but this normally only rears its head as a problem on full auto.

Likewise whilst the gun is like this it's handy to use the forward position (with the tappet spring refitted and the sector chip well out the way / full forward) to check the nozzle to bucking seal.

If you have your mainspring fitted you can blow in the front of the barrel to check pressure seal.

Again as mentioned, the other culprit is incorrect bucking combo, feed lips to long taking up feed tube space.

Or finally the hop unit is different / non original and fits differently in the reciever / gearbox but that's a big can of worms.

You are reinventing the wheel by this point!!

Stock hop unit is best.

 

[Stevo4345]

Cheers for the help, the only thing I am sure about is the tappet plate, it’s a factory part that I purchased as the original was broken when I first opened the gearbox.

Will have a look.