Jump to content

Overspin problem and Gears upgrade

Recommended Posts

I've recently got a new Specna Arms SA-B11, it's a a solidly built gun, the internals are pretty good and with a lonex m100 spring in it it fires at 310fps approx.  But I'm looking to upgrade the internals to get better trigger response and RoF so I got a Gate PicoSSR 3 mosfet, deans, 11,1v lipo and a ASG CNC 30k motor.  I installed the mosfet and deans then test fired it using the new lipo and I a lot of overspin, firing 2 shots on semi.  Then using a 7.4v lipo and the ASG motor it overspins to pulling the piston to the back each time firing on semi and this puts the air nozzle forwards pushing a bb into the hopup so it just rolls out the barrel.


How can I stop the double firing using the 11.1?


Also I'm thinking of getting a new set of gears at 13:1 or 12:1 probably from SHS.

So would all these parts work together without overspin:

13:1 or 12:1 gears

m100 spring

ASG CNC 30k motor

PicoSSR 3 mosfet

11.1v 1450mah 30c/60c lipo


Looking for any advice before I go and buy anything, thanks?

Share this post

Link to post
Share on other sites

Stay on 7.4v and try an Element M105


perhaps a m110 spring which might be too hot

BUT the spring guide might not be a bearing spring guide

So you could correct AoE a smidge to drop the stroke/fps on a slightly hot M110 spring @ 360fps


This means jack if springs are rated incorrectly but should work out about right imho without too much work


Overspin you will get a bit as the gun cycles faster - which depends on motor/gears/juice

Also worn parts like Cut Off Lever can increase overspin but gun sounds new-ish


it may come with a m95 spring though GunFire says m90 - hmm maybe but think m95

lower or weaker springs will overspin more as they don't slow the drivechain on piston release and thus more overspin

saddo's that go nutz will use heavier springs m120 and short stroke stuff but involves more work/headaches


Usually you should be able to get a gun hitting 345fps @ 20rps without major overspin

this you should be hitting on 7.4v with that new motor aprox on std gears


A slightly heavier spring like an Element m105 should work out about right imho

this will slow the drivechain a little and reduce the overspin a little

the rof might drop a slight whisker but no biggy


On a lower UK spec @ 350fps you can't really go above say 20rps unless more work involved

Usually not worth it for most people and 25rps will most certainly double fire

hence why it goes nutz on 11.1v - going too fast - DON'T TRY IT coz your piston will strip

(the box is talking to you in a funny sort of way)


If you are hitting say 18rps and loads of overspin then the spring is m80 or COL is worn

or other stuff like trolley is jumping off trigger sear really late pinched contacts worn COL etc...


You might be able to turn active braking on the mosfet if has AB

but not sure if has AB feature - think not but don't buy or use AB stuff

(motor gets a bit warmer and imho if done right few builds will not really need AB though each to their own)


So in essence pop a slightly better spring in there that is not worn or too short

should be around 170mm long than a faded 150mm spring length though this isn't set in stone

a long spring doesn't mean more power than a shorter one but old faded ones tend to lose their initial length

before anybody chimes in - I meant when people think an old spring is gonna be ok

but then find out it is faded and most likely mislabelled in a box of old crap spares

(just buy a new one one if unsure)


Keep her on 7.4v with a new M105 spring and be done with it

your battery should be about 20c to 25c

the burst or C can make a difference and 30 or 35c lipo's do pack more wallop so will spin more

The rps will be good anyway on 8mm bearings - just thinking you are pushing it a bit on a weak spring


Or go nutz on Short Stroking & heavier springs and fast gears - but I'd avoid the work if you can

just use the gun and keep its rof sensible is the best advice for now

hope this waffle helps a little bit - nice gun btw

Share this post

Link to post
Share on other sites

Thanks for the help. :D


I've looked around a bit more and found that getting a mosfet with active breaking really helps with over spin so I'll probably get a Gate nanohard mosfet and shs supershooter 13:1 gears.


What do you think?

Share this post

Link to post
Share on other sites
2 hours ago, Someingonewrong said:

I've looked around a bit more and found that getting a mosfet with active breaking really helps with over spin so I'll probably get a Gate nanohard mosfet and shs supershooter 13:1 gears.


What do you think?


Already said I'm not a big fan of AB but it won't completely solve the issue for you to go mental

By mental I mean use 11.1v or 13:1 gears

Or completely stupidly insane if you are thinking 11.1v AND 13:1 together


Answer some questions first:

What is the burst or C rating of the lipo's - both 7.4v & 11.1v

What is the rof or rps on 7.4v

Are you hitting 310fps or more/less/ lot of variation - Mall is 340fps absolute max

Have you got deans on your gun/lipo already - likely or should have

How much overspin are we talking about on 7.4v. if the piston is clearly showing in rear window ?

(is it really at the back of the box, or just showing a fresh 7.4v with 8.4v charge in it)


You have bearings which yield a extra rps or maybe two over robust bushings

Deans & mosfet & 16awg rewire give a further 15% boost aprox

(I doubt 20% unless stock wire was really really crap and multiple breaks/connections etc...)

So it will vary a bit on 20rps I initially quoted but there abouts I reckon on 7.4v


YES you COULD get an AB but it does NOT mean you can go nuts

By that I mean the gun is cycling quick it seems

When a gun starts to cycle quicker and double fires or mega overspin it is talking to you

Aggressive AB will try to stop the motor by reversing polarity on release & where heat can generate

BUT it ONLY brakes on semi on trigger release or when you have finished going nutz on auto

IF whilst unleashing hell on auto at a high spay n pray speed you have even a minor jam or misfeed....

BANG, the jam will slow the piston's return on release, the gears engage before the piston is at rest and crap happens

Hence AB does not solve insane overspin or PreEngagement risks that increase with the speed


Yes 13:1 gears slow the drivechain on piston release a little due to ratio change

but the rof will go up a bit (25% max) on a decent motor of course, but gearing should slow drivechain

(Even 12:1's do not give you 50% boost over a 18:1 coz gearing load/ratio increases (maybe 30%)

but rof increases so not for 11.1v like you are thinking - that is taking liberties

get a bigger spring m100/m105 hitting 335fps and yeah it might help but get spring first

than rush out to make stuff even faster/responsive


Yanks can use 11.1v's coz they can use m120 springs - we can't and Mall is 340 not 350

So you want Element m105 than a m110 I now realise- no more

(unless you go down m115/20 & SS route)


I think you would be wise to first of all get a new spring either SHS M100 and/or Element M105

get the fps up to say 330-335fps and see how you go on 7.4v

The motor is quite quick - a quick balanced motor on a light spring

you will only really get to about 20rps unless you want more work/expense/overspin as I said

Even with a fair bit of work I have got about about 24rps on 13:1 & SHS HT on 7.4v 25c (bushings)

But even then I'm not gonna go nutz on 36rps with 11.1v & I have a tiny 11.1v 33c which is even more grunt

(basically the 11.1v is another cell so rof goes up by 50% or 2 cells vs 3 cells)


Also as you go faster you should likely need a metal rack piston for greater durability

20rps is ok but any more I tend to use metal rack

BUT you need to understand about not taking the pi$$ especially on a metal rack

PreEngagement from going nutz will strip a plastic rack - usually that is all if ya lucky

But on a metal rack there is no weak point and stuff will break in drive chain

likely the bevel's tiny 10 teeth will go first, but could take the motor's pinion or spur etc...

(you will have a more costly mess to sort out in other words taking the pi$$ on a metal rack piston)


By all means go nutz if you wish, pop over to airsoft society & follow Legacy's excellent guide on going nutz


BUT they tend to use m120 & higher field limits so you can't take this as 100% gospel for a UK build

Many of us have learnt this the hard way - yes you can go nutz but I have kind of settled a smidge over 20rps on 7.4v

(I get fed up picking out the bits from taking the pi$$ and learnt the hard way that 20's is plenty)


Go for an AB mosfet if you like but still pretty sure you will find you can't use 11.1v on your present gun

(not unless you go back to stock motor which is likely to be much slower)

It is a question of finding that 20rps balance and living with or more money/work

you can hit a bit more with 13:1 or 12:1 gears

or go nutz and hit 32rps on 7.4v high speed motor & 12:1 SS 4 teeth balls up I made on a HOT BD160

Or DSG (over-rated) hitting 40rps on 7.4v but crap runs hotter as amps increase & batteries drain etc...

and tbh people with really quick guns are overcompensating many think

(fine for a poops n giggles project but really we find a balance of 20 to mid 20's work best in the end)


We have all been there, I've wrecked loads taking the pi$$ to arrive at the same conclusion many warned me

It also isn't how fast the gun shoots but how well it shoots & more so how well the guy holding it plays

It isn't the gun's rof but the skill of the player that usual wins the game


I'm not saying don't do this or don't do that - it is your gun so do what like with ya money & time

just be aware of what can happen if you take the pi$$ that little bit too much

I have come to the conclusion it is better to go a bit less mental and get more playtime than repair time

Edited by Sitting Duck
sorting out my many typo's - jeez my typing is crap

Share this post

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...