MOSFETs and gearbox cycling

[Lozart]

I don't see the point of plug'n'play MOSFETS really, unless to convert to semi-auto only. But I will have to look into the BWKK V2 more carefully now, because pre-cocking is something I want.

However something else which the BTC Chimera does is ROF control by timing discrete shots, so you can have your GB cycling very fast, at 30rps say, but set the control unit to something realistic like 700rpm and in effect you get about 11 semi-auto shots in a second with tiny gaps between them - apparently it sounds very cool as well as saving ammo.

Click to shrink...

Burst Wizard does that too: http://www.aegwizard.com/

(I'm not on commission by the way just offering alternatives)

My Burst Wizard is only plug and play bcause I only use it to give me a single shot burst on an M249 for a CQB site that requires semi in most areas. By leaving it plug and play I can easily whip it out and go back to full auto lunacy!

 

[Ian_Gere]

No, that is one thing I remember quite clearly about BWKK's - the ROF is controlled by voltage, so it slows the cycle to lower it. With the BTC Chimera the cycle remains at the same speed, but the shots are timed electronically. I'm pretty sure that only BTC MOSFETs do this so far.

 

[Lozart]

No, that is one thing I remember quite clearly about BWKK's - the ROF is controlled by voltage, so it slows the cycle to lower it. With the BTC Chimera the cycle remains at the same speed, but the shots are timed electronically. I'm pretty sure that only BTC MOSFETs do this so far.

Click to shrink...

The newest version is PWM based.

 

[Ian_Gere]

To me "PWM" stands for "Pulse Width Modulation" - I dunno what it means in this context...?

 

[Lozart]

To me "PWM" stands for "Pulse Width Modulation" - I dunno what it means in this context...?

Click to shrink...

I would assume that it means it's pulsing the drivetrain to control the rate of fire. Modifying the mark space ratio would allow you to change the RoF fairly easily.

 

[Lozart]

From their own site:

Allow the only real steel way to adjust the ROF of every AEG to fire and sound like a real gun in around 15 to 20 rounds per second: Full 100% battery power to cycle the gear when firing each BB just like a real steel and allow you to set the pause time in between BB firing in 0.005 second and up. The result is the smoothest real steel like firing experience that everyone had been dreaming for from an Airsoft gun!

Click to shrink...

 

[Ian_Gere]

Aha! Thanks for clearing that up then, Loz!

Thing is... I still dont trust 'em :lol:

 

[TheGrover]

Just another quick question:

whilst most 'Fets are designed to fit a certain gearbox, if i use, say an ICS L85 with a custom, bespoke gearbox, could i just buy any old 'fet, and wire it between the battery and motor, with the signal wire (or two) up to the trigger contacts and it work fine? does the specific version of the gearbox alter the performance of the 'fet besides the way it might fit inside the casing? and if there is a difference, how do i work out whether to use a v2 or a v3 'fet ina bespoke gearbox?

Thanks

 

[Sitting Duck]

stand alone fet's can be used on any gearbox

the internal ones that fit inside the gearbox's v2 & v3 are different all-in-one's so to speak

the burst wizards & proper Gate brand of mosfets are stand alone/seperate or plug in versions

that fit in stock/front/battery compartment - that is the type you would use with an L85 or

other non-run of the mill v2/3 gearbox systems

The "pause" command used in the micro pic chip isn't the same as pwm - that would be a bad idea

of lower the voltage - but pause to adjust the whole cycle timing is better

(but can't work out why really you would want to drop say 25rps to 20rps unless site said 20rps max)

PWM is used in many areas like pc fan - it send a 12v signal in a pulse pattern to keep fan at xxx rpm

this is monitored as well as cpu temp and adjust as/when needed - clever stuff

BUT PWM on an airsoft can work in theory but you would be pulsing high amps/load on that poor mosfet

a rapid high amp lot of pulse low voltage signals to trigger the fet and if the fet could respond that quickly

then poor thing would really heat up in that moment - thankfully they not using pwn on the fet but pause

command in the pic controller

Or a quick puase/countdown timer in m/secs before triggering the next full cycle on full auto

(presume either full auto or a 3/5/7 burst on full auto)

think reason some plug-in burst wizards/fets work for some and not others is mainly coz different setup

that peeps use - some may run with a high load and others a weaker faster load setup that may/may not

trigger false overloads or cause burst wizard not to respond too well

I know they work in some guns ok and others not so well and have Swiss Arms (avacado type)

and King Kong 2 wizards - though not tried these KK out yet as just got them for £10 offer with some guns

(Airsoft World net - but only on some guns - most guns don't have this £10 offer on them)

 

[straffham]

I would assume that it means it's pulsing the drivetrain to control the rate of fire. Modifying the mark space ratio would allow you to change the RoF fairly easily.

Click to shrink...

PWM also causes heat buildup in the motor, effectively its starting and stopping dozens of times a second (depending on frequency used), and uses more battery power IIRC. Admittedly my only experience of this is in model railways where PWM gives better locomotive controllability, but burnt out motors (small ones particularly) are not unknown. Admittedly the much bigger motors used in airsoft may be able to cope better.

 

[Lozart]

PWM also causes heat buildup in the motor, effectively its starting and stopping dozens of times a second (depending on frequency used), and uses more battery power IIRC. Admittedly my only experience of this is in model railways where PWM gives better locomotive controllability, but burnt out motors (small ones particularly) are not unknown. Admittedly the much bigger motors used in airsoft may be able to cope better.

Click to shrink...

Different style of pwm. The burst wizard is off for longer than its on in this case so it shouldn't be too bad.

 

[Russe11]

Do any mosfets allow the addition of an electronic fire selector?

My Sten is full auto only but I currently use a burst wizard so that I can set single shot only or 3 round burst. I am currently weighing up the option of buying a second Sten to convert into an Owen gun. The Owen has a fire selector but it would be a nightmare to make it work mechanically with a gearbox not designed for a fire selector in that location. Is there a mosfet that would allow me to add a switch to go from one preset to another?

Alternatively, would it work to use a switch to bypass a burst wizard, thus allowing full auto or not bypass it thus making the gun semi auto?

 

[Sitting Duck]

Very much doubt if pwm is used - instead they used the pause or a similar "wait" command in pic chip

pwm on mosfets would be making them trigger so fast that even if they did work at such speed/modulation

the amount of heat produced would not be good for the fet let alone motor triggering on/off at high speed to

in effect emulate a lower voltage for less rps

Where as the pause/wait of .05 m/sec per cycle would be similar to drop battery from 11.1v lipo to 9.9v life

(don't quote me on this exact voltage figure but just using it as example to lower rps from say 25 to 20)

but to be fair - i don't see this being so ultra high important feature of lowering your rps by delaying the cycle

But we will all have different requirements/setups so feel that mounting everything inside gearbox though clever

on the latest microswitch/mosfet system - just means you are putting all eggs in one basket/gearbox

Yes it saves room but to be fair - with careful planning of battery size/location most could use seperate mosfet

or burst mosfet/wizard - or lipo alarm too I guess if you have the room

but that is just my preference of seperate fet outside box - suppose if it did eveything and made tea then all in box

would be ok - but still not cheap if they come back in stock

Russel - one option could be to simply wire up a switch to toggle the supply to either burst wizard or direct to switch/motor

that way you in effect have your burst setup or just plain old simple system

though I am not sure if burst wizard would be completely ok being bypassed if it was still connected as it may have some

flowing back to it from switch/motor running on old system if you get what I trying to say.

if damage could occur then the exit line from burst wizard would need to isolated too or a some protection used to prevent

damage if power flowed back to rear of wizard

yes a 3/4/5/6 position switch - prob a rotary type switch with different small resistors fitted to it would then send an analogue

value to the controller in wizard/pic chip to say fire at X mode depending on the value the switch gives out

but doubt atm if there is some "external" port/output on most wizards/chips for this option but something I feel I would like to

have - eg: 3 burst full auto - but quickly go to 7/9 round if surrounded by more foes, or vice-versa if I find I'm low on ammo

without having to mess about holding down trigger to reprogram the burst again

I am no electronic expert at all - but have dabbled a bit with stuff and atm just trying to visualise in my head any possible

problems with numerous options that we all use/require as well as wishing to try some things myself but torn for time what

with work/family/sleep and just generally trying to have a life on top - but there are many improvements and options for what

currently - ha excuse the pun, the old school trigger/cycle system

 

[Ian_Gere]

The reason to reduce ROF, not from 25 to 20 rounds per second say, but rather from 25 to 15 or less, is so that you keep the fast trigger response and get a wider spread of fire from your 3-4 round bursts (when exercising good trigger discipline) for shooting at moving targets, or save ammo when you're using full-auto to suppress targets in cover. Some people may also want to do it for realism.

 

[Sitting Duck]

But would you still gain effective trigger response unless the delay/pause/wait only came into effect when using say the one touch 3 round burst

eg: 20 rps = 0.05 seconds per shot - now say we drop to 10rps coz easier maths = 0.1 seconds cycle

unless that came only into effect when using a say a one touch 3 or 5 round burst then you could be adding 0.05 secs to the first cycle

hopefully if it came into effect only on the burst mode then you would not be adding 0.05 seconds to each manual cycle, coz unless I am looking at

this all wrong that 0.05 sec extra timing is in effect making trigger response worse if happening all the time

excuse my ignorance if there is more to this than my noobish head is getting around and I could be failing to understand the major difference

between rate of fire and trigger response time

all the same - think a selector switch is an option I may prefer rather than mess about reprogramming or changing the burst setup/config

(a little bit of work modifying but if you that serious about this kind of upgrade then you wouldn't be wary of using drill/dremmel on your aeg)

Heck if you really wanted to go nutz on this with more bells whistles n options I suppose:

fit 2 - yes 2 rotary switches to say underside of stock or other place than you could use but not knock the switches position easily....

switch 1 - burst fire on 3 - 5 - 7 - 9 etc.....

switch 2 - pause delay of 0.025, 0.05, 0.75 or 0.1 seconds to adjust the rate of fire when using burst fire modes

of course this would have to be incorporated into yet another new generation of ACSU's

but then - c'mon what would be next - thermal heat sensor linked to scope that automatically fires at enemies ???

I mean with so many bells n whistles on there it would kinda make it a little ott or take out some of the skill some have

of having a good responsive trigger finger perhaps - any noob could pull off a perfect fast or slow 7 round burst at a

simple flick of a switch from day one

the most important thing to me atm is a trigger switch that won't fail on me in the moment on semi

or just as I close the box and start a few good test shots - only to find out - arrgh its gone again ffs !!!

 

[Ian_Gere]

It doesn't add any time to the cycle - at least the BTC Chimera doesn't: the Voltage remains the same. Taking the 20rps example where a cycle takes 0.05s - if you then use the control unit (because BTC Chimera is not just a MOSFET, it is 2 parts, one of which deals with power handling and the other which is the programmable part) to drop to 10rps, when you fire full-auto, or a burst-controlled short burst, or one touch burst (as it has all of these options), each cycle still takes 0.05s, but there is a 0.05s pause between each cycle.

Bear in mind it is also an AB MOSFET so it is capable of absorbing additional energy remaining in the motor after each complete cycle. The thing is that it will use more battery power and that power has to be available quickly, because each shot is effectively a semi-auto shot and the motor will need an initial high current draw to start it moving again, but so what? You don't go fitting an £89.99 part and not make sure your wiring can handle the current, you're using Deans connectors, and a better LiPo than some random 15C 'airsoft recommended' arse, eh? You fit 16AWG, or 14 if your receiver has enough space around the gb, and use a Turnigy Nano Tech 50/25C LiPo, plus a spare. It may well heat up the motor and/or FET more than ordinary full auto but, to quote The Beatles, "Happiness is a warm gun..." :lol:

 

[Ian_Gere]

Oops, forgot to say - you want to avoid adding switches to such a system. Switches are high resistance parts and getting rid of them is the main point of using MOSFETs.

 

[Sitting Duck]

but we still rely on 1 main or 2 micro switches usually even with mosfets but these trigger/cut off would be low voltage

as well as the one or two optional ones would be that would instruct the controller chip what mode you have chosen to fire in

the original switch design is built up with resistance/carbon/arcing but when replaced with low voltage this is drastically reduced

the possible optional select switches would also be low voltage like perhaps the revised 2 switch trigger/cut off switch in ACSU's

in fact the selector switches if implemented would be less build up than trigger/cut off switch as they not going to be in use much

(you are hardly likely to keep flicking modes/delay whilst firing all the time)

yes over time the switches - even low voltage ones would build up with a little resistance but way way less than pumping 11.1v on

the old style setup,

All I was saying about the optional select switch/switches is it would be a possible option for further consideration/development

though it is a little more modification to fit but then most "proper" mosfet install in not just a simple plug n play

my main bone of contention is with the actual old switch itself being so old in design and prone to wear/failure

That would be the reason why I would go down mosfet route atm, - keep the internal trigger/cut off lever switch simple

and then use a simple fet like pico or mess about with own N channel fet - not forgetting a low volt reg circuit etc...

then if at some later date I wish to go nutz I could go for a more featured fet/wizard like £50 Gate one

but for now am studying/thinking about updated switch and basic straight forward fet for the moment

I didn't think it altered voltage or pwm but it does add a tiny m/sec to each "additional" cycle when in burst/auto mode

they obviously thought this through with a little common sense - so initial trigger response in starting the burst would remain

it is all interesting stuff but guess reason why this isn't installed in most aeg's is all down to costs but in basic form I doubt if

low voltage & simple fet would be that much extra if makers fitted them to nigh on most of their guns

 

[Ian_Gere]

G&G certainly seem to be heading that way. Trouble is that they seem to have chosen a pretty shit FET to base their system on :lol: