A Thread About Skara Questioning His Arp-9

[Sitting Duck]

Gear ratio might depend if box is reinforced

requiring mod for 13:1's like some King Arms, Cyma's even M904G

(not all cyma v2's, the new QC Cyma v2's, the 7mm mp5's not reinforced)

Not a biggy mod if required for 13:1's

But something to consider when planning

If box is strong enough - just drop DSG in

& run a torque 28tpa with 150/160 spring option ???

Guess it depends what motor you end up getting

Lonex A1 then maybe keep stock gears

SHS or 25k or 22 TPA maybe 13:1's

Old crappy 27 tpa motor, strip & chuck in neodym can & DSG ???

But like everything, where do ya start & where do ya stop I guess

 

[Skara]

Perun installed, something must have gone terribly wrong though, as after the calibration process now whenever I plug the battery in the gun fires on its own.

EDIT:

What went wrong was me messing up the calibration.

Took it apart, tricked the unit into calibration mode and made the trigger pull a bit more substantial than the touch screen I had set

seems to be working fine now, although it's rather late now and can't test properly.

also reshimmed the box, it runs somewhat smooth now (spur gear was too tight from factory, while the sector and bevel were really loose) with only just a tiny bit of play on the sector, so tiny that if I put a 0.1mm spacer it becomes too tight.

Now we (I) wait for a zci 22tpa and 13:1s so that I can meme around with binary spam

EDIT 2:

Out of curiosity I installed one of my SHS high torque motors and ho-lee shit it's fast!

Double taps like a motherfucker without AB.

So yeah, I'll keep the stock gears and order yet another SHS HT.

 

[Skara]

Forgot to update this thread.

In the end I went for a ZCI 22tpa motor, quite slow but the semi cycle time on a 11.1 is good.

The gearbox shell, though is utter shit, or the motor is, or the grip, I can't figure it out -.-

I can't properly shim it, I did the good ol' spur first but the bevel wants to sit really high.

Tried bevel to pinion, the bevel now has zero shims on top yet it appears to be too tight, moreover the ZCI motor is really pushing against the bevel even with the grip adjustment screw completely removed.

I thought it was the gearbox shell being a bit shit, so I bought an 8mm one but the bearings I got (SHS) must've been a friday night job and they don't spin -.- stayed up until 2 AM last night to try and figure out what was going on and I'm really pissed.

I'll see if I can pick up a set of decent bushings later today and try again -.-

 

[DerDer]

A few companies seems to advertise low profile bushings. Might be worth a go?

It's very frustrating to repeatedly take apart and assemble a gearbox, if the screeching is caused by wonky bearings

rather than one's own shimming.  

 

[Skara]

A few companies seems to advertise low profile bushings. Might be worth a go?

It's very frustrating to repeatedly take apart and assemble a gearbox, if the screeching is caused by wonky bearings

rather than one's own shimming.  

Bushings profile isn't the issue.

It's how they went in and the fact that they don't spin (well one does but still, 1/6 is not good enough lol).

I'll pick up some decent ones this Saturday.

In the meantime I started dicking around with various parts and decided to try a different pistol grip.

Swapped the stock one for an old ICS grip I had and it made a world of difference!

The stock grip, as mentioned above, makes the motor sit way too high despite having removed the adjustment screw.

The "new" grip, on the contrary, almost completely removed the pinion to bevel scratching, although now it doesn't sit flush but is slightly canted to the side and the motor gets warm quickly.

There is still some gear scratching noise but that will eventually go away as soon as I replace the bearings.

 

[Skara]

New bushings in, tried spur first and it's dumping a moulinex into a bucket of nails and a spanner levels of scratchy.

Tried bevel to pinion, still scratchy but without the spanner.

Also tried with the stock motor, still the same. Good thing about these Modify bushings is that they have a little ridge protruding into the gearbox so I didn't use too many shims.

At this point it's pretty clear, I got a lemon somewhere.

I ran the thing for a couple of minutes to try and scratch the gears, the shell or anything else and locate the source. Gears are spotless, the shell has just a tiny bit of scratching under the spur (fixed by swapping a 0.15 shim with a 0.2).

Bevel teeth seems fine, pinion seems fine (I might try and swap it for a SHS one but they look identical).

With the motor inserted and the height somewhat adjusted there is just a tiny bit of play on the bevel, with the shell closed and tightened each gear has about 0.1mm of play which looks bang on to me.

There is no grease that may conceal scratches.

I'm giving a SHS HT a go, just to eliminate the motor as a cause.

I'm legit clueless, anyone got an idea?

@Sitting Duck

 

[Adolf Hamster]

tried it with just the gears in the shell spinning by hand?

also worth checking backlash, even a completely matched set of gears can sound bad if the box has them spaced slightly too far apart.

other thing worth checking is the idler in particular can commonly not be flat, so whilst it might spin freely for part of its cycle it could bind at a single point.

 

[Sitting Duck]

Motor grip/angle is my hunch

but tbh it could be anything, wire either side of motor

loads of slack in the gearbox opening & motor tower

so it thrashes about...

Motor grip OK on gearbox out of receiver ???

so the grip needs filing as it could be pulling when all fitted together to receiver ???

tried marking the box with receiver & also grip to see if grip is too large ???

something like the motor axle is not 101% inline with bevel axle,

so it is running off centre or at a minor angle if motor slightly skewed

I'd grab another grip if you got one, one that is pretty snug on box

and doesn't have a massive motor entry point to the box

so hopefully the motor is not able to thrash about once it all aligns

(hopefully in sync & in line from motor axle shaft direct to the bevel axle

so the bevel pinion is exactly at 6 o'clock & not offset)

 

[Skara]

I swapped motors with my 933.

ZCI motor in the 933 sounds perfectly fine although it wants to sit 1/1.5mm lower than the SHS.

SHS in the PDW (just the gearbox with ICS pistol grip) sounds shit, no matter how high/low I set it.

Spinning gears by hand you can definitely hear them grinding, I also had doubts about the spur/idler not being flat because when I had the box shimmed spur first, at one point it was getting stuck with the bevel. Now it spins fine though (read scratching but not binding).

So the motor is ruled out, the gears might be part of the issue and I can still replace them with ZCI advanced (my tech has some in stock, a lot more expensive than buying online though).

The major suspect remains the grip then.

Unfortunately, other than the ICS mentioned (which is also wonky as heck) I don't have any spare.

I was thinking of getting a couple of PTS EPGs for my M4s sometime soon (tm) so I could give a specna A2 a go.

Can't be arsed right now but I might try tomorrow.

 

[Sitting Duck]

Be careful of them Magpul/PTS clone grip bollox

I had a couple and some other aftermarket grips - they were shite

motor sloppy as fuck, motor grip plate seem to shove motor way out of line with axle

certain motor plates don't always fit other grips - despite looking the exact same

So come to the conclusion that most often the stock grip is kept as it usually is fair good

(sod changing grips to a more fancy looking one)

Sounds like you might have a burr or slightly wonky gear or two also

adding to stuff - sometimes a rebuild goes according to plan, almost completely flawless easy shimming

other times it is nightmare after nightmare and have to go back with an ultra fine examination of everything

Yes I fully understand how some motors, the way the armature is set on the motor's axle higher/lower

results in some motors being nigh on the max/min limit in some guns/grips etc...

also the springs on the motor tower can vary too, usually they compress right down to say just under 5mm

(squishing them & measuring in a digital caliper)

but others only compress down to say 6mm - so before you start the motor can be sitting 1mm higher

due to a motor spring with more coils in it

Then factor in the way armatures sit higher/lower on some motors and in middle of magnetic field

(like SHS & ZCI)

then no wonder swapping motors can result in a very different motor height setting

and sometimes this can be beyond the tolerance of motor height adjustment on some guns/grips

fucking nightmare it can be - I know some will be tempted to add some shims between grip/box

to space the grip if motor sits way too high - well as temp fix or to see it if improves

(I guess if you had 4 screw threads in box you could add 2 to left/right to slightly tilt motor angle)

but really this is a temp fix/test or bodge trying to see if motor aligns a little better

but really try another grip/motor/pinion/gear-set or something and go back over it all again

end of the day you know by the sound if it is right or not, backed up by amp draw

but you know when it sounds right - it's your own fault for being a fusspot when dealing

with lapse Chinese tolerances is poxy toy guns

 

[Skara]

So, smol update.

Since I have bought them PTS (genuine ones, not clones since they were just as expensive lol) grips I transferred one of the stock specna A2s on this gearbox..

ZCI motor still sits too high, SHS motor sits fine, can be adjusted, but the box is grindy as fuck (most likely because the bevel is super high, or because the gears are fucked or something is wrong with this new box).

At this point I will proceed in this order:

1) reshim (spur first) to accept a SHS HT and use the zci in one of the specnas, probably the 933;

2) revert back to the stock KA gearbox and keep this 8mm one as a spare.

Shame, as I thought it would work

 

[Skara]

I think it's the bevel...

Can I swap it with a different one or will it fuck the ratio?

 

[Adolf Hamster]

I think it's the bevel...

Can I swap it with a different one or will it fuck the ratio?

you can, but you run the risk of issues such as backlash or different teeth profiles.

as long as you're checking for those it's all good. i've done mis-matched builds in the past this way.

 

[Skara]

you can, but you run the risk of issues such as backlash or different teeth profiles.

as long as you're checking for those it's all good. i've done mis-matched builds in the past this way.

Nevermind, there was some crap stuck in a bearing

I've officially reverted back to the stock KA gearbox, whenever my PTS grips arrive I'll test the ZCI motor in my specnas and use the SHS HT in this one with the stock grip.

I might even get a game day with the thing before retiring

 

[Skara]

I give up.

Shimmed for the SHS motor and A2 grip, put the gun back together and installed the zci motor by mistake.

Fucking bang on (the adjustment screw is just a smidge from rotating freely).

What the fuck.

Aight, imma keep it this way, in the meantime I managed to get my ring finger caught by the piston while testing (don't ask how, because I legit have no clue) so now the gearbox is lubricated with blood

This gun is cursed, it's probably going to kill me in my sleep someday..

 

[Adolf Hamster]

Aight, imma keep it this way, in the meantime I managed to get my ring finger caught by the piston while testing (don't ask how, because I legit have no clue) so now the gearbox is lubricated with blood

how?

 

[Skara]

how?

Finger, this is piston.

Piston, this is finger

*now kiss*

Pretty much what happened, the crime scene was the rear cutout section of the box.

 

[Adolf Hamster]

that is definately a new one.

been stabbed plenty of times by springs and various pokey bits but never a piston......

 

[Skara]

Fucking bang on.

Ran flawlessly throughout the day.

Very pleased with it, just need to test if it can lift 0.32s.

 

[Adolf Hamster]

Fucking bang on.

Ran flawlessly throughout the day.

Very pleased with it, just need to test if it can lift 0.32s.

i'm assuming you're running a macaron or equivalent so the answer is i'd be surprised if it didnt.