Except Systema, I found most of 3 round burst / sniper mode mosfet set on the web those are only "time delay" type that means when you release trigger, the mosfet is still giving power for xxx (ms) then stop. When your AEG change part such as different ratio gear, spring or battery the "timing maching" is needed to be setup again. And one of my friend was always asking me to repair his G&G L85 since the semi function part is never be available even he walked in to Taiwan factory.
In the very beginning I copied Systema to install a IR reflection optocouper to control firing. Why not "reflecting" for me? It is because the sector gear is too hard for drilling. I spent 90 mins for only 2mm depth on the drilling bed. Also I thought Systema has a major issue. When there is dirty with grease in the gearbox, that blocks the holes on the sector gear or IR sensor. That makes the gun never stop. Even I had confirmed this issue from my friend just last month, Systema had programmed safety function which stops firing in seconds if sensor cannot detect IR. The real truth is, gearbox is always dirty. It is not a good design to me. http://youtu.be/2nSytRu3X34
For my Play-Hard-Theory I spent 3 years for my mod. I used magnet sensor to detect magnet field replacing IR sensor. In the normal single shot test, by the active braking mosfet, it stop gear momentum prefectly without any pressure of the spring http://youtu.be/p3YYeM-NY_M. Then I "taught" the computer to delay stopping the motor or xx ms, it needed to try because of your parts settings, to success the sniper mode. I set it stop at the last teeth at 12.6v Lipo so I would stop at any voltage. Then I also taught it to shot 3 rounds in semi mode. Not like L85 after auto firing and change to semi. When you trigger the 1st shot it normally NOT to fire but gears move to the sniper mode position. Haha My gun does not have this issue.
With this design I am asking my friend to give up fixing the L85 because I can make the L85 function to any AEG.
I have 12 orders of this mod now. Hugh job!
Super Shooter 7075 CNC Aluminum Gearbox (durable for sniper mode)
M14 air nozzle (little bit longer)
SHS 18:1 gear set + delayer (perfect shimming)
cheapest trigger switch mod with a small switch (only need the shell)
trigger spring removed (light trigger)
M130 spring (law limited)
full tooth piston with bearing head and bearing spring guide
factory base cheap motor
Magbull DD 12.5"
PDI 500mm 6.01
Magbull metel hop-up
Magbull metel body
Magbull motor grip
Sliverback Venus 4700mah 150/75C