My gearbox is CYMA and not the best. But I want to keep it in good shape. I'm running a lypo and I'm pretty sure I'm giving it a pretty good workout every time I fire a round.

Can someone please send me a schematic that's been used and tested for a simple mossfet. I'd rather spend 10 bucks on parts and 20 minutes soldering than to replace my gears anytime soon. I want to keep them happy.

A MOSFET will not protect your gears.

MOSFETS as we know them in airsoft are just switches activated by the stock trigger switch mechanism. Think of them as a really awesome relay switch. The computerized ones control the MOSFET switch with different modes of fire, active braking and ROF. Right now you are sending a lot of current through your stock switch. This causes arcing that will erode your contacts and can lead to a failure in the stock trigger switch. The big plus to using a MOSFET is that they can handle lots of current, switch very fast and don't have any moving parts.

Here is a basic MOSFET with parts list.

ASC: How to Make a Basic MOSFET Switch Unit

I'm not sure what you think a simple MOSFET does that would save your gears any trouble. A basic MOSFET unit simply redirects the heavy load of current through itself as opposed to the trigger switch, saving your trigger switch from arcing and carbonizing. It has a few other side-effect benefits like better efficiency on the battery draw and faster trigger response, but a simple MOSFET has nothing to do with your gears.

Edit: Yeah, what Mini-T said.

If you're talking about a more advanced MOSFET-based fire control unit that has added features like active braking and full-cycle completion, then yes, that would help your gears. But there is more to it than simply soldering parts together. There is programming the PLC - for which you need to know the C programming language and have the proper equipment to burn the C code you write to the ROM.

If you have experience with programmable micro-controllers and the equipment / software to develop on them, you could do it. The source code for the Trigger Master series is about 925 lines long. As a professional software developer, I average about 400 - 500 lines of code a day, so you'd be looking at about 2 full days of work in AVR Studio (the software used to write code for AMTEL AVR Microcontrollers) assuming you got every line right the first time - which I can promise you never, ever happens.

With all that said, the schematic for the current generation of airsoft MOSFET-based fire control unit is here:
http://extreme-fire.com/SW-Cheetah-2N-500-sch.gif

And an article on getting started with AMTEL AVR Microcontroller programming, including the part you have to buy from DigiKey to hook your computer up to the ATTINY85 chip use in that schematic to properly compile the C code onto it, is here:
http://imakeprojects.com/Projects/avr-tutorial/

Edit: Here's a design that features active breaking (but not full cycle completion) and doesn't require any programming. However, it'll cost you as much as just buying a much more advanced Trigger Master, since you need to get a circuit board printed for it.
http://filairsoft.com/forum/showthread.php?t=52330

^what they said.

Another benefit to the micro controller fet unit is that it can be made to monitor battery voltage and shut the gun down in case of low voltage. But to build your own cheetah, you're looking at about 30-45$ in parts I believe.

Yes a simple fet can be made for cheaper, but you're also only getting the trigger switch benefit from it as the others have said.

To protect your gears, you'll need a proper shimming, bushings or bearings strong enough that they don't deform under heavy load, corrected angle of engagement (AoE) on the piston teeth and properly set motor height. And some luck that you got a strong set of gears that's well balanced (read quality) so they spin without wobbling.

There's cheap chinamade ones(mosfets) for like 10-20 bucks, but they've been reported to burn out pretty quickly, and a wire set/trigger switch can be had for about that price.

the right shim job should be all your gears need. It will allow them to spin more freely and not jump up and down while spinning. When you cycle your gun does it screech or whine at all?
I dont think you need a mosfet. Specially for just a 7.4V lipo. They dont cause nearly as much heat as the 11.1V lipos do.

(01-30-2012 12:42 PM)liquidsquirt Wrote:  the right shim job should be all your gears need. It will allow them to spin more freely and not jump up and down while spinning. When you cycle your gun does it screech or whine at all?
I dont think you need a mosfet. Specially for just a 7.4V lipo. They dont cause nearly as much heat as the 11.1V lipos do.

First off, thanks for the info guys. I was under the impression that a simple mossfet would allow my gearbox to complete a full cycle even after I let go of the trigger. Thus releasing the tension that may be there if it stops half way through. I emagined that over time it would fuck shit up.

Liquid, I have to get you to shim it for me and replace my bushings. Can you recommend bushings?

(01-30-2012 04:55 PM)bullfist Wrote:  Liquid, I have to get you to shim it for me and replace my bushings. Can you recommend bushings?

modify stainless steel ones are good, so are systema. cant really go wrong with either. stay away from bearing bushings, they can blow out and cause all sorts of problems.

systema 1000 oiless are a sure buy for bushings.

stainless steel... no soft metals like brass. and Ithink some shims come in copper.

STAINLESS?!?? NO WAY STAINLESS!?!?! Area 1000's are a soft metal and ABSORB oils.. ICS Upgraded bushings are COPPER.

Soft or Hard they both run the same but costs are different and so are the way they work. Neither is better or worse.
I have run Area 1000's in a TM G36C, ICS M4 and CA M15A4 CQB Compact (Yes that little beast I had) all running 350-400 FPS
and completely abused on ammo. They ran flawless. I have run Copper in ICS M4's and they sound soo much nicer with them in.
ICS Gear Axles are actually smaller than standard gears and hence the Copper Upgrade bushings to fit them properly.

Bearing Bushings are bad : FALSE COMPLETELY FALSE (Unless in a full auto setup)
Running a Semi Auto setup on Ceramic Bearing Bushings gives you a killer smooth cycle and huge decrease in frictional force in the
mechbox. I will run them again if I ever get a TM M14 to own. Cheap arse bearing bushings will cause you issues no matter what.
Buying Real Airsoft Brand Name Bushings (Not Modify, or CYMA junk) will run in a semi setup great.

interesting, in the info I've read, there were some reported issues of copper and brass flaking or deforming. While nobody really had much bad to say about stainless bushings and shims.

(01-31-2012 04:33 PM)lurkingknight Wrote:  interesting, in the info I've read, there were some reported issues of copper and brass flaking or deforming. While nobody really had much bad to say about stainless bushings and shims.

It might make sense, stainless just sounds better and it's not very easily worn down. I think it depends on how the copper or brass was heated and molded. I have seen copper bolts flake and crack so what's to say your bushings won't do the same over time?

In hawkesbury I used to work in a machine shop and we worked with titanium making the peices that hold the visor on bomb squad helmets.

How about getting your hands on some titanium bushings? I've searched and can't find any info.



P.S. I like the idea of this mossfet, I already have the parts to make it so I think I will. It prevents the full charge from the battery from having to go through my trigger switch every time I activate the gun. Right?

(02-01-2012 02:06 PM)bullfist Wrote:  P.S. I like the idea of this mossfet, I already have the parts to make it so I think I will. It prevents the full charge from the battery from having to go through my trigger switch every time I activate the gun. Right?

it depends on the unit and how its set up to work,

all route power through the switch, how much depends on the unit.

some route a minimal ammount to sense when the trigger is pulled, and send the bulk of the power stright to the motor. these are generally the kind that have the fire rate controls, burst functions, and active motor braking. as well as voltage cutoffs for lipo batteries.

some send all the power through the switch, their only real purpose is to prevent too much power going through, and some have battery monitoring, and lipo voltage cutoff.

some replace your switch entirely with a microswitch. it works prettymuch the same as the first mosfet. but installation is 100% easier.

(02-01-2012 02:40 PM)Durak Wrote:  

(02-01-2012 02:06 PM)bullfist Wrote:  P.S. I like the idea of this mossfet, I already have the parts to make it so I think I will. It prevents the full charge from the battery from having to go through my trigger switch every time I activate the gun. Right?

it depends on the unit and how its set up to work,

all route power through the switch, how much depends on the unit.

some route a minimal ammount to sense when the trigger is pulled, and send the bulk of the power stright to the motor. these are generally the kind that have the fire rate controls, burst functions, and active motor braking. as well as voltage cutoffs for lipo batteries.

some send all the power through the switch, their only real purpose is to prevent too much power going through, and some have battery monitoring, and lipo voltage cutoff.

some replace your switch entirely with a microswitch. it works prettymuch the same as the first mosfet. but installation is 100% easier.

I was talking about the one that I was linked to in a previous reply.

the DIY kit that mini-T linked, yes would save your switch wear and tear but would have no features such as battery cutoff, or burst. if you want those you would need a more advanced mosfet like the DIY ones lymbo linked.

you can get prebuilt and preprogramed mosfets for anywhere from 20-150$

just an idea for whats out there and what you can do with a mosfet. http://www.awsairsoft.com