What is a MOSFET?

[GingerBreadMan]

As the title states, what is a MOSFET? I get that is primary purpose is to prevent arcing at the trigger contacts and that this is done by running an extra wire to the MOSFET from the trigger. That is what I think I understand but looking online shows many mostest with pre cocking, active braking, passive braking and others. What is meant by this?

 

Also, is there any decent guides out there about soldering as I am utterly useless.

[two_zero]

>What is a MOSFET thread?
a thread asking what a MOSFET is... this one for example http://www.airsoft-forums.co.uk/index.php/topic/24659-what-is-a-mosfet/.. or this! http://www.airsoft-forums.co.uk/index.php/topic/24660-what-is-a-mosfet/

[GingerBreadMan]

Yeah, my ipad is really playing up no idea why it posted three times!

[jcheeseright]

A MOSFET is a metal–oxide–semiconductor field-effect transistor, in airsoft terms what it does is provide a 'remote switch' for running power to your battery directly to your motor, bypassing the trigger switch. The trigger switch will have a very, very small amount of power redirected to it and when that circuit is made, the MOSFET opens up the gates for the rest of that power to go through to your motor. It results in massively increased conductivity which improves trigger response and saves your trigger contacts (which were handling 11.1v for example... now handling 0.1v).

Pre cocking, cycle completion, ROF control etc are all features of computerised MOSFETs, the principle is the same in that the trigger switch is bypassed, but there's extra circuitry to control timing and gear positions etc. Precocking for example when set up correctly will hold your piston on the last couple of teeth with the spring compressed, so your next trigger pull only requires the motor to turn a tiny amount to fire, this for an AEG is pretty much 'ultimate trigger response' as it's more or less instant. PTWs use this method to achieve their instant response. Rate of fire control on the more modern MOSFETs is done by cycling the gearbox almost in semi, very fast; the gearbox will cycle for one shot... wait a bit (measured in milliseconds) and then fire again, wait a bit.. fire again, this makes every cycle of the gearbox the same speed, but the rate at which BBs come out of the barrel can be changed at will.

 

Active braking is a feature a lot of MOSFETs have now, even really small ones like the Gate PICO AB, when you release the trigger on your gun without an active braking MOSFET installed the motor doesn't stop immediately, it'll carry on spinning under it's own momentum for a very short time, with high torque and high voltage setups this can sometimes result in the gearbox cycling twice with one trigger pull, known as overspin. Active braking MOSFETs counter this by applying reverse current to the motor for a short time to stop it dead the very instant you release the trigger (or the cut-off lever disconnects the contacts for you in semi-auto), this stops overspin and in theory allows the gearbox to stop in the same position (or thereabouts) every time you pull the trigger.

[two_zero]

Yeah, my ipad is really playing up no idea why it posted three times!

figured as much, but I couldn't resist

[Sitting Duck]

Active braking "can" generate a little more heat (certainly don't make the motor run cooler)

normal fets are negative or npn - triggers the negative supply on/off

with active an additional positive fet (pnp) is used to reverse polarity to stop motor as said above

 

In most "general" builds and if a high speed/torque motor is used then it probably will be ok without AB

Most high speed/torque motors use neodym magnets (silver)

as opposed to cheapo stock ferrite magnets (black)

 

Neodym magnets are MUCH stronger than ferrite - if you can turn a motor over easily that is a ferrite

a neodym is very hard to turn like stepper motors, these stronger neodym motors stop much quicker

than ferrite motors that roll on & on when power is cut.

So if using a stronger neodym motor you "may" not need to use active braking unless you are running

a higher speed setup or DSG

Using older ferrite motor and higher volts then you may find you need AB but that is if the old stock motor

will be up to the job and if it can take any extra stress using AB fet.

Me thinks most will upgrade motor to neodym so AB probably won't be needed unless you are going nutz

 

If you are fitting the usual "external" mosfet then you can just do the main rewire on the switch/motor leads

try a normal non-braking fet that should be fine for most setups - if it does over run or double fire then it is

very straight forward to replace the NB fet with an Active Braking fet is my humble noobish opinion

 

Soldering - there was a couple of threads on soldering deans and stuff a week or two ago with a vid also

most soldering is a lot down to using decent iron,solder & perhaps flux plus a bit of practice

not hard but like most stuff the more you do it the better you get (usually)

 

deans thread:

http://www.airsoft-forums.co.uk/index.php/topic/24451-what-deans-plugs-do-you-use/

 

There a number of ways to wire it all in, v2 gearbox's are a little more awkward than v3 as motor wires on v2

are inside box and if rear wired you have extra wire(s) running by motor spindle but you can run signal wire(s)

externally if you are careful. When using thicker 16awg motor wire space gets tight inside a v2 where as v3 motor

wires are external so to speak.

 

It is not that hard if you can solder ok - all down to using decent stuff + practice and then add a little common sense

[GingerBreadMan]

Thanks for the help guys i understand some of the features more now. I am definitely looking into getting a mosfet soon as im now trying to making a switch to lipos and deans connectors. What are some you would recommend?

I will be fitting it into a G&G cm18

Thanks SittingDuck, that thread is very useful and i am also going to get some spare wire and extra connectors to practice soldering.

 

Also can anyone recommend/link a decent lipo charger

Thanks

[Lozart]

IMax B6 AC charger, Gate Electronics Mosfets (Nano AAB is a nice one).

[dex]

The Gate Nanos are good, a little chunky for my liking. If you want something small have a look at the Gate Pico.

[Josh95]

If you want a technical representation of how a mosfet works watch this:

I'm actually learning about transistors right now its really interesting

[Lozart]

The Gate Nanos are good, a little chunky for my liking. If you want something small have a look at the Gate Pico.

 

The new Nanos are smaller but I've just taken delivery of the new Pico AAB. Very nice - prewired and heatshrunk so better (in my opinion) that the old barebones style Pico. It'll be going into either my M4 or my AK so I'll let you know how that goes!