Embarking on a med/high ROF build for the first time...

[Krydel]

So i got lucky at the bookies recently and decided to splurge my winnings on some nice new shiny gearbox internals for my G&P MOE, currently entirely stock but for running an M90 spring. Its due a compensator to arrive in the post (I switched the outer barrel for a longer, different thread, so the original CW flash hider doesn't fit) and for me to whack a few more accessories on it, but its pretty much done externally for now.

 

 

Now, the first piece of advice most newbies seem to be given when attempting to do gearbox work is to take it slow and make sure you are well-read and know what you are doing before you start. I'll be doing just this. I will not do anything without know what it will do to my gearbox first and will certainly not be just throwing all the parts i've bought in and expect them to work right off the bat.

 

The purpose of this thread? Just to check that I'm not going to be making any horrific mistakes when it comes to building my new gearbox (I will be building a new one in its entirety, so i have a stock and an 'aftermarket' one). I already have these parts after doing some reading up on whats good. I know the gears are good for the money, though not necessarily fantastic in their own right, but can't stretch to Siegetek gears right now. Also, i will be running a 300mm prometheus EG barrel / prowin hop chamber combo when i get them.

 

The Parts List:

 

• Spare G&P 8mm Gearbox shell - any parts not listed below will be stock G&P.
• Modify 8mm Ceramic Bearings
• Lonex M120 Spring
• Lonex Shim set
• Lonex A2 High Torque Motor
• Lonex Sector Clip Delayer (if required)
• SHS 13:1 Steel Gear Set
• Lonex Steel Ball Bearing Spring Guide
• Lonex V2 Cylinder Head
• Lonex Air Seal Nozzle
• Airlab Sorbothane Pad (70D)
• Lonex POM Piston Head
• Lonex Red ‘Extreme Toughness’ Piston (to swiss cheese)
• New 16 awg wiring
• Lonex Motor Connectors
• BTC Spectre MOSFET
• 11.1v Li-Po (when i get one, that is, running 7.4 at the moment)

Adhesives & Lubricants:

• Finish Line Teflon Grease (60g tube) - for general gearbox greasing
• Loctite Super Glue (3g tube) - for the sorbo pad
• JB Weld Epoxy Adhesive - for gluing the bearings into the shell
• Silicon Oil (o-rings, bearings, etc)
• Rubbing Compound - for inside of cylinder and other areas of friction in the gearbox such as piston rails (can anyone recommend a good one - dont have this yet)

The Plan:

 

1. Don't use any of the aftermarket parts initially.

Why? I am going to strip down my stock gearbox and do the basic 'DIY mods' and adjustments, maintenance and whatnot that doesn't require any part replacements (apart from sorbo or equivalent for AOE correction). This is to ensure I know exactly what i'm doing and i'm confident fiddling about in gearboxes before embarking on something more ambitious and to ensure any learning curves or mistakes are made here and not with my expensive parts. These are, in no particular order:

(a) Degrease, clean completely and regrease / lube as appropriate. 

(Use dremel to polish moving parts/areas of friction

© Proper shimming

(d) Correct angle of engagement with sorbo and piston teeth removal

(e) Radius the front of the gearbox where the cylinder sits

(f) Epoxy the stock 8mm bearings into place

(g) Might swiss cheese the piston to practice, not that i need to.

(h) remove a small amount from the front of the tappet plate

 

2. Once i have my stock gearbox in a state i'm happy with, I can move onto my medium/high ROF build. I'm aiming for a 30 rps as a minimum, anything else is a bonus as far as i'm concerned.

(a) Install the above parts list, making sure to do all of the above, but this time also:

(i) swiss cheese the lonex red piston to lighten it

(ii) remove the ball bearings from the piston head to lighten

(iii) sand the tappet plate front (is this even a good idea with a high ROF setup?)

(iv) Install Spectre, new wiring, motor, new gears etc

(v) With a M120 spring, i'll be firing over 350fps, so I will be short stroking a few teeth (or however many it takes, i'll probably try 2, then 3, then 4 etc) to get down to a desired level as well as eliminating the possibility of premature engagement. If you guys think I could get away with an M100 (which i assume is the stock G&P spring) without running into premature engagement issues, or that I should at least try it out with the M100 before going straight for M120, let me know.

(vi) Testing - fire a hundred rounds or so through it, disassemble and check for pre-engagement wear or any other problems. 

(vii) Check feeding - if any issues, try sector delay chip.

 

3. Be happy?

 

 

Conclusion:

 

So overall, I would just like a bit of a glance over what i'm about to do, offer any additional tips or warnings, and someone to point out any glaring flaws in my plan. The most contentious is probably going to be the short stroking, and this is the one area there's a lack of consensus over in my research. With £20 gears, i'm not scared of taking some teeth off, though. Pre-engagement sounds pretty scary stuff, so I don't know if i'd like to risk it with a weaker spring, which I use now.

 

Thanks so much in advance to anyone who takes the time to help me out and check this over for me.

 

 

[Tinkerton]

I'm in the process of rebuilding my MP5K with a medium/high ROF set up. I had it set up in a really poor version before, where it hit 38 RPS with nothing more than a dual sector gear and an 11.1v lipo.

 

Bevel and spur gear were stock, motor was stock (TM EG700, i believe) wriring and trigger was stock.

 

I've got a set of highspeed gears (13:1, iirc), a high torque motor, big fat chunky wiring, and a mosfet. I'm hoping to reach somwhere near there, considering people get over 50RPS with dual sectors.

 

Personally, the list you put up looks good, with a few exceptions - I've heard nothing but good things about SHS gears, supposedly the only ones better are seigetek, which are pricey, to put it politely.

 

The sector gear delayer might not be needed - at these sort of fire rates, it might just lead to double feeds.

 

If you're insistent on using bearings, use 9mm ones. They dissipate the heat better, and last longer (in an 8mm bearing, the actual bearing ball is tiny. in 9mm they're slightly bigger but not much.)

 

Don't bother with motor connectors - just solder the wires directly onto the motor tabs. Connectors lead to resistance, which leads to wasted powah, which leads tto ROF drops. Bad times.

 

Don't use sorbo to adjust AOE, especially in a high ROF build. Sorbo 'works' by compressing to a certain point when it's under the pressure of piston and spring, in a high ROF build, such as anything over the 30rps you're after, it's got roughly 0.03 seconds per complete cycle, let alone the compression phase of the piston slamming into the cylinder head. Chances are, it wont compress down to the level at which you adjusted AOE to, which could probably cause pre-engagement and misalignment and all sorts of nasties. Bad times.

 

As an aside, if you DO end up suffering from pre-engagement, you're going to have to short stroke AND up the spring rate. In mk1 of the mp5k build i think i had about an M150 in there, and it was putting out about 250fps (when it actually fired, stupid hicaps). 

Higher spring rate means faster piston return to battery, which is good. Short stroking means you dont use all the potential energy in that spring, which means (theoretically) you could put an M190 spring into a 6 tooth short stroke and still not be breaching 340fps (hop, barrel, cylinder volume dependant, etc).

 

Apart from that, it all looks good, keep us updated!

[jal3]

Here's my cookie-cutter build:

-Guarder Tappet plate

-Modify Nozzle*

-SHS flat cylinderhead / or any non-plastic flat cylinderhead*

-SHS or Guarder "M140" spring***

-Flat alu head, most are fine. No bearings. Better quality plastic PH's are ok too at M100.

-SHS full rack piston (TT0035/36)

-Metal springguide with bearings*

-8mm Kanzen Synergy bearings (or other, just not some cheap with small balls)

-Siegetec 14:1 gears**, SS3-5***

-Slower neodymium motor. I like to build my own out of neodymium cans and Classic Army HT cores.

-11,1v 2200mAh battery

-GATE PicoSSR2 MOSFET + 1,5mm2 wiring + not-tamiya-plugs

 

Makes a solid 35rps gun with excellent semi and stabile output at that (or higher even) rof.

The parts are also rather cheap.

Most stock ARL's are fine for this; the spring on it is more important.

 

* = these parts are more dependent on fit; use whatever fits instead.

** = if SC is too expensive, you can go with SHS 13:1, SHS 16:1 or lonex 16:1. 16:1 obviously slower, but you can counter that with a G&P M160, Element high speed, Systema magnum or similar fast neodymium motors. Slower semi will result. Fyi, 18:1 usually lands me around 35rps with those motors and SP140, so 16:1 is plenty fast.

*** = Shortstroke 3-5 teeth depending on resulting muzzle velocity. Start with 3. Do NOT go from 3 to 5 even if 3 is way too high. It's not linear. It is based on being 15 below the spring rating, eg. "M140" will yield 125m/s with 0,28 and hopup dialed in.

Aiming for 345fps, you should use SP120 spring with 5 teeth off and maybe 1 spacer. But start with 3 and work your way to it.

 

I know many are happy about sorbo, but i do not recommend it. Feel free to experiment ofc. The pre-made sorbo cylinder heads these days are very well made.

 

I don't recommend single stocktube batteries for highspeed builds. An alternative would be to use a cranestock with parallel batteries, or parallel 3-part stick batteries in the front (should just squeeze under the rail).

[Skarclaw]

Not worth making its own topic.

 

 

Gun: CA G36, deans, higher gauge wire, 7.4 1300 Mah 20c+ continous

 

The ROF and trigger repsonse is not where I'd like it. I'm guessing this is the motor as its 9 years old now. I havn't got a ROF figure but it is sluggish, put it that way. By contrast my stock g&g lr300 purs away nicely, although its got a slightly higher spec battery.

 

I'm not gunning for a super ROF monster, I'd just like it a bit nippier and to be confident zapping away on semi without thinking its going to lock up. To this end I've been suggested that the following parts are fitted:

 

- SHS 16:1 Gears

- SHS High Torque motor

- Airfet (tbh I'd like this just cause)

 

FWIW: I have a TM EG1000 new in box sitting at home. Is the HT motor worth the £30? 

 

Thoughts? 

[ollie_ty]

Skarklaw, Go for 13:1 gears, and id go for a Lonex A1 or A2 instead of the SHS, Ive found that they heat up way too much.

 

Krydel, just buy another gearbox shell. that way you can build and learn, without having to sacrifice the current setup.

[Krydel]

Go for 13:1 gears.

 

Krydel, just buy another gearbox shell. that way you can build and learn, without having to sacrifice the current setup.

 

Yeah i have a spare shell with most of the stock internals left inside it i'll be using

 

This is the first i've heard about *not* using sorbo, shall have to look into that a bit more i guess.

[Tinkerton]

Well, it's just a case of simple phsyics, really. at what rate does sorbo compress down? how long does it take to go from fully compressed to relaxed? with something like that where the actual strike face position of the piston head is variable, AOE is going to be shot to hell.

 

The only time i'd really consider using sorbo is in a stupidly high FPS semi-only set up, where the actual rate of fire isnt going to be much over 3 shots per second, or so. Even then I'd probably end up going with a stupidly long airbrake, instead.

[jal3]

Skarklaw: A neodymium motor is one of the best upgrades in performance gun. The SHS HT (Black) are fine; they'll give just under 30rps full stroke, which is great for non-shortstroked setups. I've installed plenty that way. I don't think they're better or worse than other motors in terms of heat/durability. Most AEG motors will last forever unless they're factory broken or installed sub-optimally.