Motors and their relationship to FPS

[Baroc]

Hey guys, I have a marui-clone AK47 (upgraded with tightbored,hopup unit, new rubber hopup nub and a high-speed motor).

Originally this gun was shooting aprox 390-405 FPS with the stock motor and spring and a simple tightbore.

Recently I purchased a "X High Tech High Speed Custom Motor for AK" and slapped it into my gun. The ROF is WAYYY too high, my electric drum will feed into it, but my high-caps cant keep up with the ROF (about half the time the gun fires it's not actually shooting a BB). Now I rechecked my velocity recently and it's now around 300-315 FPS, a substantial drop....

I'm assuming this is cause by the motor not pulling the stock spring back enough, in order to spit out more rounds per sec?

I'm aiming to have the gun fire around 400fps (the limit on most outdoor fields). What would I have to do to get to that point?

I realize that I will lose some ROF and that is PERFECTLY fine with me (as my mags don't load right anyways since it's too high). Should I just swap out this new motor for a "slower" one? (If so, any suggestions?)

What would you guys do in my situation?

THANKS !
-Dan

[L473ncy]

That's impossible the motor only turns the gears to pull the spring back. No matter what the motor will spin the gears until the last tooth of the sector gear when it will then release the spring/piston to push air out the barrel. Either the motor will pull your spring or it won't (or struggle with pulling it but still able to pull it), there's no "half pulling". It's totally discrete, either it does or doesn't.

You probably have other problems like the main spring is worn out or that the piston o ring isn't sealing or something. I don't know what it is but it's not related to the motor.

[Cobrajr122]

If the ROF is too fast, maybe the sector gear is picking up the piston before it can move forward completely. This would lower the amount of air going into the barrel and thus the FPS.

Have you switched back to the stock motor to see if that makes a difference?

[ThunderCactus]

the high rof might be causing back suction or misfeeding or improper sealing
changing motors doesn't affect fps, but changing rof drastically can
If the sector gear was picking up the piston before it got all the way forward, you'd strip the piston or gears very quickly

[Rusty Lugnuts]

IF your using a lipo or 9.6v nihm , try dropping back to a 8.4. That may give you both wishes

[Baroc]

I'll try and switch back to the stock motor right now (the connector nubs broke off to it'll be a b*tch to solder on, but ill give it a go).

Otherwise, maybe it IS the spring that is worn out, I've put maybe 10,000-12,000 rounds through this gun. I've played in Sand dunes, thick forest and snow alike... it has seen it's fair share of abuse.

How often should one switch out the spring on a primary-AEG?


I've tried using a 9.4, as well as a high and low end 8.4, the 9.4 is by far the worst, but the 8.4's are both still too fast as well lol.

[Cobrajr122]

Originally Posted by ThunderCactus

the high rof might be causing back suction or misfeeding or improper sealing

This seems more plausible.

[Baroc]

got the old motor back on (was hard to do the motor tabs are both broken off -.-).

my FPS now is still around 305-315 fps, so I'm assuming that means my spring is worn/old and needs replacing.

thanks for the info guys!

[Styrak]

Motors have 0 effect on FPS.

Your error was not chronying your gun before starting to work on it.

[ThunderCactus]

Springs don't wear 100fps, they hardly wear 20fps. My springs haven't lost any power after 4yrs
Whens the last time you opened your gun and relubed it?
Grease gets old and tacky, causes compression problems

[XZIVR]

Maybe needs a sector delayer to ensure the thing is feeding properly.. Also, when chronying you are in semi auto, so the sector shouldn't be picking up the piston before it is all the way forward.

It's possible something was just on the edge of wearing out (think piston oring) and the new motor managed to accelerate the wear to a critical point? My guess would be that or 'you put it back together wrong'

[MaciekA]

Originally Posted by XZIVR

My guess would be that or 'you put it back together wrong'

bingo. It's also possible to have upset or damaged something that was in good shape before. A drop of 100fps is a lost hopup spring, torn bucking, forgotten tappet plate spring, chewed up frontal piston teeth from PE, damaged nozzle, etc. Just do a whole gearbox and compression system check from front to back.

[lurkingknight]

Originally Posted by MaciekA

bingo. It's also possible to have upset or damaged something that was in good shape before. A drop of 100fps is a lost hopup spring, torn bucking, forgotten tappet plate spring, chewed up frontal piston teeth from PE, damaged nozzle, etc. Just do a whole gearbox and compression system check from front to back.

Also this.

Something isn't parked where it should be and your air seal is not optimal.

Does it feed fine with the old motor in it? If yes, then with the new motor you will need a lower power battery OR a sector clip delayer.

[sammynac99]

I remember reading something about how A very high rof could effect FPS, as if there Is more then one round being propelled thought the barrel at a time it could effect compression, check out airsoft GI's video on building high speed guns

[Rusty Lugnuts]

Find the air leak! With a higher Fps, his rate of fire will slow down, building a high fps, high ROF mech box takes way more effort than just tossing in a better motor.