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Recommend me a motor and gear set?

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Im currently looking into some gears and motor to go into my custom built M4 reciever and gearbox.

The gearbox i am going to be using is a non split Retro Arms V2 Gearbox as seen here:



Ill be using Modify 8mm Ceramic bearings,


Gear wise im am looking for best for buck, price isn't a problem, i've heard Sigetek make the best gears but currently full sets are like unicorn tears at the moment. Motor wise i am undecided normally i have used the G&P M120 but if theres anything better let me know.


Long version

I currently own a HPA'd SAI M4 rifle.


I want to use the same upper receiver as it has an Edgi Barrel, Prowin hop up chamber with an R-Hop by Kingdom of Airsoft, it is laser accurate!

The lower receiver i want to keep it exactly the same.


With the onset of some fields not liking or outright banning HPA use i want an AEG version of the same gun and i have decided to just build a lower receiver so i can swap the lowers out when i want HPA or AEG.


ERGO i plan on building a no holds barred lower, i will be getting the same receiver set so it all matches, a gearbox from Retro Arms as i have heard the make the best CNC gearboxes, I plan to install a GATE Titan o i have almost the same trigger response as i do in my HPA gun.


I have most parts chosen except the gears and motor.


Gear wise i don't want any stupid high rates of fire, say maybe 20 to 24RPS, i have previously used the generic G&G gears and found them to be pretty good but was wondering if there's anything better out there.


Spring wise it will only be pulling either an M100, M105 or M110 at most.


I have looked at Siegetek, SHS, Ultimate ASG and Modify, i like the look of the modify ones as they are already apparently shimmed but will they work in the Retro Arms gearbox? Siegetek i have heard never break or strip but they cost a bomb and a full set is difficult to find in the UK.


If you can advise me on a motor too, again normally i have used the G&P M120 motor but is there anything better? I have heard that ASG Ultimate motors are rebranded Tienly ones which are apparently good which use NIB magnets.


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Motor wise either a SHS / Rocket HIgh Torque or a ZCI 22TPA High Torque.  I've heard good things about Lonex, Tienly and ASG which is in the next price bracket up.


I only ever use SHS / Rocket gen-4 gears these days, pretty solid design.  Best around seem to be Seigeteks at the moment but I've never used them, also Retro Arms get a good mention from chatter on Facebook.  

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Agreed: SHS/RA Motor & gears will do you proud for a modest 20-24rps build

you could hit say 20rps on the SHS Torque (really a balanced motor than a slow ultra torque) with 18:1 gears


you could hit say 24rps on the SHS Torque with 13:1 gears

These are ROUGH ball-park max figures on bushings so ceramics add a couple of rps

you could most likely use 16:1 with ceramics & get near the performance of 13:1


All figures will depend on motor - shove in a slower way torquey motor like 22tpa

Or use a titchy burst rating 15-20c then rps will be lower


You could use 13:1's then use Titan to tweak the final setting - ask Hangtight


As for all ceramics - perhaps consider using just one bushing under spur...



Just long durability where all the stress forces meet in the drivechain


Apart from that reckon SHS gears with SHS/RA motor will mesh nicely as is

And be more than up to the task

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Ive yet to have modify ceramics break under the spur gear as i am only using a M105 at most TBH.


I think in that video he used an M120 spring, maybe too tough for bearings.


So you guys would recommend SHS 13:1 or 16:1 gears right??


Looking more for quick trigger response so may be a balanced motor, not too torquy not too high speed.


Been looking at the ASG Ultimate ones as well and theya re tickling my fancy TBH

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Your gun, your build etc....

Infinity motors are superior & Siegetek are of course ergh Siegetek


Said many times ask 10 people and you will get at least half a dozen different replies

All depends on budget available - I get use same shell in same receiver to ensure exact compatibility etc.....

Internals is not just the name/cost but how well it is all fitted together imho


Reason SHS motor & gears not just price but many agree they mesh very well together

For instance there are two rough basic checks worth performing with bevel & motor/pinion


First off all do they mesh at correct angle ?

Many stock bevels may mesh ok-ish (some may not) with stock motor/pinion

place them both together and try to ensure all teeth are meshing 101% then examine the angle

Ideally you want a true 90 degree angle with the teeth meshing fully

So that full power is transmitted using all of the available teeth

(kinda similar in ensuring correct motor height etc...)

If the bevel & spur meshing at say 80 degrees then even set perfectly yoy may only have 75% teeth transmission

So in a perfect world you would like to see/feel 90 degree meshing than 95 or 85 degree meshing

Extremely bad example pic....

Related image


Just coz the two gears actually mesh at perfect right angles means jack though

roll the motor/pinion around the bevel and feel how well the teeth actually engage

Most of the time decent stuff will work with other decent stuff

But it is wise to do a quick check to see that these two foundations of the drivechain mesh great

(and roll smoothly as they engage one another)


Whatever you decide it is worth give these two gears the once over how they mesh etc...

You still got the motor angle/height shimming crap to sort out but it is worth a quick check imho

(even if you buy all shs stuff which "should" mesh very well together)


If the two gears' teeth mesh at right angle smoothly meaning when the height is set all

or nigh on damn it all the teeth are being used to transmit power smoothly

how well this all shimmed/set/meshing will result in lower amps & heat/friction genereated

(basically cooler gun and battery (as well as build) will last longer)


SHS & SHS should mesh well together but no matter what you choose/decide

still give it all a quick check when assembling

It "should" help to reduce the shrilliness if them bastid gears all mesh sweetly

(well that is the theory of it all)


Your CNC box should not have a re-enforced arc on top of spur

so you can fit higher speed gears in than be limited to 16 or 18:1

(or require a dremmel mod to fit 13:1's in there)

So fit what you like 13:1's is fast enough though

Most 16:1's are actually 17.25:1 and not worth upgrading for speed from a std set

(ok if building from scratch but not a great improvement over 18:1's (18.65:1)


Have a think, decide for yourself as it is your gun

just perhaps check how well the two actually mesh smoothly

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For a 350fps build then ASG 30K, SHS 13 :1 gears and 7.4v with the Titan will give instant trigger response and around 22rps. If you intend to use more rapid semi auto fire then you'll get more mileage out of ASG 22k, 16:1 gears and 11.1v. This will be fine with up to an SP120 spring or a bit higher if you want to go DMR.

The ASG motor pinions mesh nicely with SHS gears, and they bear no resemblance to the Tienly motors I've seen. They're very well engineered with proper bearings, big brushes with leads twice the size of the ones on SHS motors, and properly terminated rather than being jammed under the end of the brush spring. The armature is balanced by being drilled rather than having lumps of epoxy stuck to it, and the magnets are very powerful. They run smooth and cool... But I'm a tart, and to be honest the SHS/RA motors get the job done very well, especially once you've soldered the brush leads to the brush carrier.

And be aware that the RA gearbox can be an awkward fit in some (quite a lot it appears) receivers, sometimes needing a fair amount of attention with a Dremel to sort. I don't know if the new ones are an improvement. I'm not sure I could bring myself to buy something that nice and then attack it!

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23 hours ago, Hangtight said:

And be aware that the RA gearbox can be an awkward fit in some (quite a lot it appears) receivers, sometimes needing a fair amount of attention with a Dremel to sort. I don't know if the new ones are an improvement. I'm not sure I could bring myself to buy something that nice and then attack it!


Nice to know mate, I ahev done some research and it appears that RA gearboxes fit G&P bodies very well AFAIK.


Ill probably go with the ASG 30K, SHS 13 :1 gears and 7.4v with the Titan

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My primary has that combination, and it's excellent. The settings on the Titan can take a bit of tweaking, depending on how low friction your build is. Wish you hadn't told me the RA gearboxes fit well into G&P receivers...

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Hangtight's setup is a solid option for trigger response.


I know this convo seems like it's over but wanted to say that of all the gearsets I have found Siegetek and Lonex to have the least and most consistent backlash from pinion to piston.


Also seeing as your using high end 'fets I would assume you'll be using pre cocking any ways for ultimate near GBBR/HPA response?


You also are not looking for silly ROF or FPS


Which brings me around to agree with a much less stressful setup;

BTC / Titan

High discharge 7.4V


20/18:1 Siegetek / Lonex

Bushings not bearings

Circa 19-22 RPS

Less gear whine / load

Higher longevity


Trigger response will be there; high C rating, quality motor and pre cocking will assure that.


Tune the spring to deliver your FPS with the lowest resting preload, this will speed up cycle time again due to reduced load.

Obviously this goes hand in hand with cylinder volume matching and air seal. :D

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I need to do more experimentation with the higher ratios and 16TPA motors. There seems to be a magic point when unloading the motor leads to the same rate of fire as the lower ratios, but with higher efficiency.

What sort of current draw are you getting with 16TPA /18:1/7.4? And how difficult is it to achieve 20+rps. That's the sort of ROF you associate with 13:1 gearing.

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If you only need upto 360-ish FPS you dont need buckets of torque, its swings and roundabouts, a 13:1 / 20RPS setup will naturally have a very high torque motor and is capable of pulling a serious spring.


With the extra revs (and equal torque) a top quality 16TPA can provide over a standard balanced setup motor it has no problem pulling an extra 4RPS out the bag on upto M100.


I havnt measured current draw for that but i cant imagine it drawing more than 15A sustained / in auto.


To the OP, glad your going for an ASG Ultimate, doesnt make sense to build a gorgeous gearbox and put a (perfectly good SHS ZCI) but not really nice motor in it! :D


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Out of interest, apart from everything else, why is everyone recommending bushings and not bearings?


Whilst i understand that the bearing under the spur gear might get crushed in high stress builds, what im looking to make is hardly high stress IMO?


Would i be ok in placing bushings only around the spur gear and leaving the ceramic bearings for the bevel and sector gear?


I used to us the Modify Ceramic Bearings in one of my long gone (as in sold) AEGs and they seemed fine?

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Yes a bearing under the bevel may get loaded in the wrong plane, IE axially not radially

Bearings only like load radially (single ball race as used in airsoft gbox)


I doubt many bearing will fail, the reason i personally use bushings instead of bearings is that all bearings have a degree of play to allow them to roll.


We want consistent gear meshing, wether a bushing is under load or not the clearance remains the same, this is not always the case with bearings.


Add to that bearings have moving parts for dirt to get in and increase tolerances, and that bearings that small are inferior to the strength of a relative bushing.


Quality bushings are also made self lubricating... impregnated sintered alloys and phosfor bronze for example


In a nutshell we buy all these fancy things, spend ages getting minimal backlash, 0.0005" shimming etc etc, the last thing you want is a variable part.


And yes your build is far from high stress :)


I love the idea of an awesome upper with interchangeable HPA / AEG lower


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Ah i see


hmm you have put me in a bit of a spot because i have already ordered the ceramic bearings haha


Oh well another build one day perhaps.

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If you open up a G&G with very soft bronzey bushings after say 12 months

The bushings under the spur and bevel will have considerable wear

Look at ye olde plastic bushings and same place spur deffo & under bevel also

(they go a bit oval-ated)


EVERYBODY will have their own take on crap as I said

But under the spur is where the most stress takes place out of all 6

(followed by under bevel but under spur is the #1 area of "possible" wear & failure)


IMHO you have two options:


#1 steel bushing under spur & other 5 ceramics for max smooth rotation


#2 Steel bushings under all 3 gears & ceramics on top - a 50/50 mix of durability/speed


either will suffice - you can use half a ceramic set & save/sell the others or keep spares for another build

Using #1 of just one bushing on spur will give max rotation and the bushing will lift the spur slightly

or the spur on the bushing will only need say a 0.1mm shim and not rub on lower sitting bearings

In a 3 x bushing build with little room the spur can slightly rub on the other 3 bushings if shimmed ultra low

(I have dremeled the other two bushings a whisker to ensure the very low spur spun freely)


Often bushings - I've mixed both regular & cross types leave little room for shim room

means you don't get a massive amount of choice when spacing out the gears on bushings vs bearings

I've ran out of space with all bushing on chunky SHS spur gear before and dropped a 8mm bearing on top

(that gave me a little extra room to shim up with & spin sweetly)


Every single build is different & everybody has their own variation or method/reasons they do what they do

Yes ceramics are stronger/smoother than std bearings so you should be ok doing all 6

But I had a std 7mm crappy D-Boys bearing box go $hit in 15k and thought F*ck that $hit again

(yes 7mm bearings are real crap but the hassle in having to rip it all apart again so soon means sod all bearings)


I gladly drop one or two rps on bushings and build it sweetly means very little lost for peace of mind (hopefully)

It is up to you what you decide but I'd at the very least consider option #1 if not #2

(guess see how it all starts to fit & shim up once you got the bits together & go from there)


SHS gears will do ya proud, Sean Connery has got into teching and is all he uses...




OK soz I'll get me coat


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Of course if you wanna go friggin' nuts you can splash out for gimmicks...


Brushless Motors are starting to finally make some inroads - WTF are they are on:

£200 - do you know how many crappy guns I could buy with that !!!

Well a bloke on fleabay is flogging one for £150 with zero feedback - yeah I'll pass


or from here still silly money ffs:



French review monsieur :


Novatech - didn't they build Johnny Five from Short Circuit

Oh no that was was just Nova I think


Annnnnnnd VFC are working on some stuff too....




Yeah f*ck all that - think I'm stick with £30 or so motors for now

but interesting all the same though ye olde brushed motors are going to be around for a while

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Interesting stuff but too expensive in my mind to be getting brushless motors.


Like you ill still to normal brushed motors for now as i want to use the GATE TITAN.

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Sometimes wish I'd never bought a Titan. It's starting to get expensive to put them in everything. ;)

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Well its done now, had to wait over 14 days for the Retro Arms gearbox which was the last piece.




Performance wise its more or less exactly where I wanted it to be, it is shooting 308FPS on .25g BB (or about 1.1joule) using G&G BBs. It has a rate of fire of 16BBs per second so a little bit slower than what I wanted but I think this is ok running on 11.1v LiPos. No air seal issues between the air nozzle and hop up which is great though there were some in the cylinder itself but that has now been sorted.


One weird this is it has a combination of bearings and bushings, the bevel gear is all Modify Ceramic bearings but the spur and sector gear have bushings in the lower casing and Modify Ceramic bearings in the upper casing. The reason for this was because the Modify Ceramic bearings poked out too much in the retro arms gearbox and interfered with the selector plate so bearings had to be used as they sit more flush.


I can’t tell you for accuracy as I don’t have a big enough garden, next time I go skirmishing ill take both lowers and see how the electric performs against the HPA, HPA lower will be the default lower.


Also this has near instant trigger response which was what I was aiming for as I play semi auto games more than full auto ones at my site.


Lastly I don’t know if its me or it is an issue, when I shoot it I swear I can hear a whine from the motor as if its not properly seated or engaging the bevel gear, everything seems to work ok and checking the insides after a few hundreds shots reveal nothing amiss. Then again I haven’t owned or shot an AEG in over a year and a half so I may be much more used at hearing quieter HPA guns.


Anyways for those interested spec wise:

·         Receiver: G&P Salient Arms licenced M4 receiver (both upper and lower but only lower is being shown

·         Buffer Tube: G&G M4 Buffer tube

·         Pistol Grip: Magpul PTS MOE Grip

·         Mag Release catch: APS Mag release in Gold

·         Trigger: APS RAF Trigger in Gold

·         Gearbox: Retro Arms CNC Version 2 non split gearbox (without hop up chamber)

·         Selector Plate: Retro Arms Selector plate

·         Spring guide: Retro Arms Quick Change Spring guide (came with gearbox)

·         Spring: ASG Ultimate M105 Spring

·         Piston: SHS blue light weight piston 14 teeth all in metal

·         Piston head: G&P xploder polymide piston head

·         Cylinder: Generic G&G Cylinder for M4s

·         Cylinder Head: Generic G&G Cylinder head (Teflon taped)

·         Air Nozzle: SHS M4 air nozzle

·         Tappet Plate: Generic version 2 gearbox tappet plate

·         Trigger Contacts + MOSFET: GATE Titan rear wired (got the complete set too)

·         Gears: SHS 16:1 gear set

·         Bearings/bushings: Bevel has both ceramic bearings, Spur has ceramic in upper case and bushing in lower case, Sector has ceramic in upper case and bushing in lower case.

·         ARL: SHS ARL

·         Motor ASG Ultimate 22000 motor (and wow this is powerful)

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Lovely looking bit of work


One question - is that 16rps on 11.1v ???

Coz f*ck me the Titan is either pausing like nutz or something is up


A lame G&G stock with a crappy 18k grey motor on 11.1v & std gears would be about that or just over

Remember you rewired, probably deans and ceramics etc... on 16 or 17.25:1 instead of 18.65:1


I would consider plug in a RC power meter and shooting a short 5-10 sec burst on auto check ya amps

if you are above 15amps on a modest build with a 22k motor 16/17:1 gears m105 something is up

the motor height/bevel/angle ain't quite near perfect


Now you might be running it on a lamey 1200mah 15c 11.1v then maybe that might explain it a little

but on a decent 25c 2000mah you should hit 20rps even with a 22k motor imho


something like this:


Image result for rc power meter


or the cheaper one:


Related image

have to solder your own deans on cheapo £6 one but plug it in and give it a burst to see the amps its pulling

fast speed motors on std gears or balanced motors on fast gears should hit about 18a to 20a tops

slower motors & not so quick gears 15a tops

absolute sweet stuff is 12a & nudging 20rps on 7.4v 25c is best I have got so far

(my meter might be out a smidge or I just got very very lucky on that one I think)


amps are not everything - but the amps & sound helps point just how sweet it is all shimmed up & running

lovely build indeed sir - beautiful stuff

just when you get a chance maybe test the amps coz you might be losing a few rps

(or Titan is slowing/pausing the cycle/rps)


Other thing is mag misfed a bit giving you a much slower rps

(had that before - haven't we all)

Best one is stripping a box down to pieces coz it not feeding right

can't be mag - it is a mid cap

nope the bb's were getting stuck in the snakey bit of spring

and I know always try more more mags etc.....

But was 101% certain mag was fine coz bb's were showing/droping out when removed

but not enough force to feed coz they jammed at snake/bend

ARRRRRRGGGGHHHHHH - yeah that mag is somewhere down the garden


More I think about it you could have misfed on chrono or titan pausing the cycle

coz 16rps is not exactly instant snappiness - 20+ is what I'd start to call snappy

(but you got micro trigger so yeah quite responsive I guess)


Run audiocity thingy or BPS meter on your phone - though phone app is hit/miss

(likes a certain kind of sound to work - often says crazy stuff like 58rps - wtf, 18rps ahh more like it)

This I have used but like I say was a bit hit/miss due to sound or where you recorded sound from

(or with barrel or bare box running etc... not perfect but can give rough idea if it works ok)



just saying you could have dropped a few rps due to something daft I reckon

see how it goes - lovely looking bad boy/girl         sweeeeeeeeet

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That motor is pokey for sure!


I think you will always hear something motor wise if you predominately run HPA or GAS.


I would say give the motor a few K to run in though, I think they are noisier new.


Could be an issue there tho, if the Titan settings are stock then I'd expect 16rps on a 7.4 at that gear ratio


Also you could lose a slight amount of noise from running a non full metal toothed piston.


Very nice setup!

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@Sitting Duck


I reckon there is a pinion to bevel gear issue.


When i shimmed the gears starting with pinion to bevel i forgot to anticipate the presence of wires and so shimmed the pinion to bevel gear, then bevel to spur and so on. While without the motor in the gears span smoothly and even moved if you jiggled the gearbox about. But with the motor and wires in the pistol grip i think the wires have pushed the motor up way too far as the motor adjustment screw has to go in quite far before it engages the motor and even then only does half a turn before it feels like the motor has gone too far in. I have tried to run the gun without the motor and physically push the motor with my thumb and it does in my opinion sound better.


TBH i have always had a problem with pistol grip floor plates pushing the motor up too far, ill probably take the whole thing apart again on Monday as im super busy over the weekend with other stuff. 


Oh and the batteries i am using are VP 1000mAh 20c 11.1v LiPos


As for the mags, i know they can keep up as my HPA gun runs at 30RPS (but only in 5 round bursts as i am a sensible HPA owner) and the mags feed flawlessly.



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Really is a piece of eye candy, bet you love rocking that thing!


You do have a serious problem to address tho...

I've spotted the difference, there's no QD sling plate on the AEG lower... slacking :D

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6 minutes ago, Davegolf said:

Really is a piece of eye candy, bet you love rocking that thing!


You do have a serious problem to address tho...

I've spotted the difference, there's no QD sling plate on the AEG lower... slacking :D


Yeah i know, i could not find a similar one in time and the only one i found the same cost £35. I aint paying £35 for just a small chunk of metal with holes in it. Ill keep my eyes peeled for one as my sling only has a QD attachment to it.

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