MOSFETs

UPDATE September 9, 2013 - Things just got "Pico" sized with the new PicoSSR2s from Gate. Now there's absolutely no reason NOT to install one.

UPDATE October 1, 2012 - Some things have changed since the initial writing of this article - namely the introduction of the Gate MOSFETS. I've updated the document to incorporate these changes.

Should you run a MOSFET in your AEG? Should you get an active-braking MOSFET? What about other features? There is no doubt that MOSFET technology has finally reached Airsoft and is here to stay. But is it for you?

MOSFET vs. No MOSFET

We didn't use to run MOSFETS in our guns simply due to cost. MOSFETs typically costed between $30-40 for a basic home-brew basement special one that somebody pieced together, but since the introduction of the Gate GDS-4005 MOSFET, we've been installing them into every gun that has come across our bench. Because we're always in the mindset to not take down something that's nor broken, we're not going to tear down all of our AEGs to throw MOSFETs in them.
With the introduction of the Gate GDS-4005 basic FET priced at around $20, now there's almost no reason not to get one. The unit is professionally designed and comes with a 12-month warranty - something that a lot of home-brew solutions do not offer. The form factor is also quite attractive and the package size is really small.

However, having said all that, the cost of a FET is still a bit more expensive compared to a set of replacement trigger contacts. The important consideration here is - what type of setup do you run? High-voltage, high-discharge lipo batteries? If so, then you may be taking down your AEG frequently to change out burnt-out contacts. A FET would serve nicely in this role. We simply cannot ignore the obvious performance benefits of a MOSFET system - overall increased system efficiency. When pursuing just that last round per second, sometimes a MOSFET is the answer.

Another consideration is space. For those running full stocks, boxes, or batteries in the front space is not an issue. But for those players with batteries inside the buffer tube in an M4 or AKs with folding stocks, space is at a premium and sometimes the ability to fully-collapse the stock is important. A MOSFET cannot just fit anywhere and takes up valuable real-estate in these tight spaces. Thankfully with AWS Airsoft coming out with their Raptor and Stealth units for V2 mechboxes, these concerns have been addressed but they do carry a hefty price tag. Finally Gate Electronics has come out with their basic FET with a ridiculously small form factor and extremely cost-effective price.

With miniaturized systems like the AWS' Raptor and Stealth units inside the mechbox, they are subject to increased levels of heat and can lead to electornics failure.

Another consideration is that introducing a complicated MOSFET into a simple mechanical system may lead to a decreased level of reliability during play - although with a quality FET, that should not be the case.

Active Braking vs non-Active Braking

Somewhere along the way somebody thought that active braking was a great idea for airsoft guns. But the fact is that while your MOSFET will immediately brake your motor mid-stroke and stop fire once the trigger is released, the immense force required to suddenly stop the motor while it is running full-tilt is extremely taxing on the motor, especially the new high-torque neodymium magnet motors. Typically we recommend that if you had to purchase a simple MOSFET, for the sake of making the circuit smaller and reducing wear and tear on not just your motor and the rest of your internals, choose a non-AB MOSFET.

Special features - Burst Function, Lipo protection, etc.

In addition to increased system efficiency, some of the more tricked out MOSFETs have some pretty neat features that would otherwise not be available - such as a programmable burst function, automatic battery cutoff if you are running a lithium polymer battery and pre-cocking of the piston (useful for DMRs). Advanced functions like ROF control and the ability to interface with tracer and magazine monitoring systems make MOSFETs hard to ignore. Whether or not these features benefit you as a player on the field and whether these benefits outweigh the cost and potential drop in reliability is up to you to decide.