Highspeed RPK

[DatJames]

So after my MG42 died due to the gearbox shell going kaboom I need a new LMG...

Getting very confident with V3 gearboxes (Owned a few AKs now) and V3 gearboxes are alot easier to find then a MG one :P ...So just wanting a opinion on the part list I have currently in my head

My field allows full auto for LMGs but only in short 1-2 second bursts so I want ALOT of RPS so part list goes
Retro-Arms 'Speed' trigger V3
Lonex A1 (Kinda non-changeable as I already have as I wanted to test in another gun)
SHS 13:1 Gears
Unknown piston (Polycarb with only 1 steel tooth but has been in multiple guns with barely a mark left on it)
590MM 6.03 ZCI Barrel (I know my cylinder volume will be low but I just want 0% chance of the BB hitting the outer barrel...RPK in question will be a CYMA which comes standard with a 500mm barrel which seems too damn short)
SHS Delay chip (Incase gun starts to miss-feed...Will also be re-wiring the drum mag with a 7.4 LiPo on a pressure switch to handle the ROF)

NOW...For the main part I need advice on: Active braking mosfets.

This setup will be on a 11.1 so its gonna have overspin...Question is: Fix it with a AB mosfet or short-stroke a few teeth on the Sector gear? ...What are peoples thoughts on AB mosfets on guns that will 99% of the time be in full auto?
Also bare in mind if I go the AB mosfet route If the motor does feel like its getting too hot I can hot-swap the mosfet for a non AB (Gonna use a Gate NanoAAB so could swap for a SSR as they use the same wiring setup)

ANYWAY...Any tips and advice is highly appreciated!

[sj_asc]

Re: Highspeed RPK

The AB FET is a sensible option for countering overspin, however it does increase heat and can also wear brushes and even the comm faster. Another alternative is to use a motor with stronger magnets - The magnets used in Lonex motors from A1-3 aren't that strong as far as they go and therefore will take longer to slow down when the power is cut.

In short, if you can avoid AB then by all means do, or if you have the funds then opt for a computer controlled FET that has adjustable braking.

The A1 motor is also very fast indeed and in conjunction with an 11.1v pack, even with a poor discharge rate will still be way too much for the rest of the setup to handle with the UK power level considered and without modification.

For most high performance builds, I would suggest the following modifications as a minimum;
* AoE correction - on a full cylinder this will eat a little of the usable volume in exchange for far superior lifespan on the pickup teeth.
* Avoid Polycarbonate as the base material for pistons, particularly those with the plastic is most of the rack - Polycarbonate is simply not suited for dynamic loading applications, time and time again this material has proven it's self unsuitable for such use. Using one of these you will at some point, sooner rather than later end up with an unexplained initial pickup tooth failure and no wear elsewhere to explain what went wrong.
* Low resistance wiring throughout, this includes motor connectors, ensure that the rating of the wiring runs throughout the wiring loom for maximum efficiency - it may sound a bit OTT to some, but in setups such as the one you have proposed where you are opting for a Lonex A1 which is a motor that pulls a lot of amps, you will see the difference.


As per the rest;
Barrel - You could run the 590mm tightbore with a non ported cylinder, and it will be, even with the AoE volume losses considered still usable. Where you will find the losses will be with heavier bbs where the muzzle energy will fall sharper than it would in a batter matched config. If you are just bombing around dumping bags of .2g's and not worring about optimal performance then it will be okay.

High ROF - The biggest issue here will be keeping the main spring site legal whilst ensuring that the piston is returning fast enough for such a high rate. For a full stroke setup with a Lonex A1, 13:1 gears and an 11.1v pack, the already borderline site legal M100 won't cut it.

In order to get a more suited list of parts/config to recommend, what sort of figures of performance are you looking for?

[DatJames]

Re: Highspeed RPK

The AB FET is a sensible option for countering overspin, however it does increase heat and can also wear brushes and even the comm faster. Another alternative is to use a motor with stronger magnets - The magnets used in Lonex motors from A1-3 aren't that strong as far as they go and therefore will take longer to slow down when the power is cut.

In short, if you can avoid AB then by all means do, or if you have the funds then opt for a computer controlled FET that has adjustable braking.

The A1 motor is also very fast indeed and in conjunction with an 11.1v pack, even with a poor discharge rate will still be way too much for the rest of the setup to handle with the UK power level considered and without modification.

For most high performance builds, I would suggest the following modifications as a minimum;
* AoE correction - on a full cylinder this will eat a little of the usable volume in exchange for far superior lifespan on the pickup teeth.
* Avoid Polycarbonate as the base material for pistons, particularly those with the plastic is most of the rack - Polycarbonate is simply not suited for dynamic loading applications, time and time again this material has proven it's self unsuitable for such use. Using one of these you will at some point, sooner rather than later end up with an unexplained initial pickup tooth failure and no wear elsewhere to explain what went wrong.
* Low resistance wiring throughout, this includes motor connectors, ensure that the rating of the wiring runs throughout the wiring loom for maximum efficiency - it may sound a bit OTT to some, but in setups such as the one you have proposed where you are opting for a Lonex A1 which is a motor that pulls a lot of amps, you will see the difference.


As per the rest;
Barrel - You could run the 590mm tightbore with a non ported cylinder, and it will be, even with the AoE volume losses considered still usable. Where you will find the losses will be with heavier bbs where the muzzle energy will fall sharper than it would in a batter matched config. If you are just bombing around dumping bags of .2g's and not worring about optimal performance then it will be okay.

High ROF - The biggest issue here will be keeping the main spring site legal whilst ensuring that the piston is returning fast enough for such a high rate. For a full stroke setup with a Lonex A1, 13:1 gears and an 11.1v pack, the already borderline site legal M100 won't cut it.

In order to get a more suited list of parts/config to recommend, what sort of figures of performance are you looking for?

Well I have already decided against 13:1 gears (As the Lonex A1 in my E&L AK seemed plenty fast with stock 18:1) and spring wise I was planning on using a M110 (Yes this would be hot as the tight-bore + Spring would probably sit it around 360-370FPS) But would wear it down with some garden plinking (Cut a coil if it came to it)

In the end I just want a gun capable of just emptying its mag ASAP but without a needing to be treated like its always gonna break when it can. Specifically this gun is replacing my old MG42s role so similar performance would be preferable (330-350FPS @ 1400RPM with enough accuracy to hit someone at around 30M) ...Even though Semi-auto will 99% of the time never be used...I want to know when I do switch to it there will be no double-feed issues as this would just be annoying :P