P90 stuck on full auto - fixed

[CJay]

hey guys i gots a small problem with my P90 - pretty much brand new internals and replaced all the wiring

last night at a game it started to fire in 2 round burst in semi - shortly afterwards it reverted to firing full auto 100% of the time reguardless of the setting (well safety still works lol) was wandering if anyone has had this problem or can think of what it is - i'm gonna open it up tonight probs anyway agaion but its just in case theres something specific with the V6???

thanks.

[kalnaren]

Is it an echo1 P90? Crunch had the same problem with his. Could perhaps be a faulty cut-off lever?

[CJay]

nah its a TM P90 but just looking at it i don't think the cutoff lever is doing the job - I'll go into more detail lol - replaced the internals to fire with an sp120 spring - works amazingly but with an 11.1 lipo 20c i think the rof may be too much for the original type guarder steel gears - the notch on the gear that controls the cutoff lever don't seem to be making much contact anymore and I'm thinking that systema high speed gears may turn the trick here - is there much difference in the wear on the guarder original type and systema high speed?

would it be worth going to torque-up gears?

[Azathoth]

I have a similar problem too.

My setup is

stock spring, piston, piston head,
systema bushings
stock TM gears
11.1 lipo

I did notice that the gun was shooting only auto, looked inside the box and couldnt find any problems.

I stress tested the gearbox on auto, fired 3 high caps in 1 long burst. then went to try semi and it works without any problems. I have no idea what happened. So i opened the box, everything was great. Recharged the battery and the gun shot full auto only again. Just for shits and giggles i ran through another 3 highcaps. Semi worked...

Switched to 7.4 Lipo without a LVC and the gun shoots semi no problem.

[CJay]

Hmmm you know that kinda makes sense to me now. I'm wandering if on the p90 u need to upgrade the spring controllin the return on the lever with that fast rof. If it's spinning fast enough it won't allow the lever to fully depress before it hits again on semi. How is ur rof on the 7.4? I also fully upgraded all the wiring with 14 guage wire. Would it be worth going back to stock wiring?

[Azathoth]

With the current setup my ROF is 18 with a 7.4 and 24 with the 11.1. I have a magnum motor that i want to install, i think that should add 5ish to the ROF.

Why would you want to go back to stock wiring?

[CJay]

the stock wiring worked fine but i didnt wanna risk melting anything on it - wandering if the wiring has something to do with the change cos it worked perfectly up untill i changed it!

[ShelledPants]

I had a very similar problem, it turned out that the cut off lever was getting stuck, all I did to fix it was unscrew the cut off lever, clean and grease the area, and replace it. Problem solved. With a well greased lever, you shouldn't need a stiffer return spring for it, so give it a try.

[Nova316]

Im sure you need a new cut off lever, it might be to worn down to the point where it doesnt catch anymore. The 2 rd burst is a sign that its the lever not catching the sector gear anymore. Just replace that and you'll be fine.

Happens on both my M14 and M4, where semi would fire semi, then 2-3 rd burst, then just straight full auto even on Semi

[Crunchmeister]

Yeah, my E90 has that problem. It shot fine for about a week, then started giving me 2-3 round bursts in semi. Then finally it was full auto. I took the gearbox out of the gun. Cycling like that, I couldn't get the semi to engage either. So I'm assuming the cutoff lever is broken. I didn't bother opening the mechbox to inspect any further. I only use auto anyway and I'm planning on installing a triggermaster in this gun eventually, so no big deal...

Originally Posted by ShelledPants

With a well greased lever, you shouldn't need a stiffer return

Dude, that sounds SO wrong...

[CJay]

Originally Posted by Crunchmeister

Yeah, my E90 has that problem. It shot fine for about a week, then started giving me 2-3 round bursts in semi. Then finally it was full auto. I took the gearbox out of the gun. Cycling like that, I couldn't get the semi to engage either. So I'm assuming the cutoff lever is broken. I didn't bother opening the mechbox to inspect any further. I only use auto anyway and I'm planning on installing a triggermaster in this gun eventually, so no big deal...



Dude, that sounds SO wrong...

I was thinking of it myself - with all the wiring done externally it makes the P90 an easy gun to install it on and then i won't even have to worry about the damned lever - just to be clear the lever is steel - is there anywhere where u can buy a reinforced version??

correct me if I'm wrong but also if u use the trigger master the lever becomes irrelevant right? in theory u can remove it with no ill effects on a P90 provided u have the chip?

[kalnaren]

I thought the trigger master still required semi-auto timing to enable it to gauge burst timings.

[CJay]

probably knowing my luck and if i remember correctly i think ur right there lol - i installed a fet unit on my HK416 and i remember having an issue like that :S

ok so does anyone know where to get a cut off lever for a P90 then

[CJay]

ok guys fixed the damned thing - id wager that anyone using a high power battery on the p90 will have the same problem eventually.

Problem:

NOT mechanical in nature at all - mechbox is fine - if ur lever looks unworn and ur sector gear is unworn then likely they are fine!

It's actually a wiring problem - or rather a high current problem, let me explain. basically the contacts on the P90's trigger mechanism are primarilly responsible for the transfer of power between the battery and the engine like any other gun so they take the full current of almost 32 AMPS through it when using an 11.1 25C battery (like min - just for example). from what i remember about electronics in school - when you have that high a current going through thin copper contacts like the P90 has then you are going to get some residue build up on the contacts - this causes a slight short in the electrical system and a slight dust will layer the area around the sparks on the contacts. on my P90 the dust had clogged all of the runners that the sliding parts of the switching assembly ran on and also caked the contacts entirely.

SOLUTION: simply remove all of the damned gunk in there and accumulated dustings of oxidated materials and it fixes the problem - I'm assuming that this is gonna be a constant problam with the P90 (or indeed any gun) using such a high powered battery - the reason its worse than the P90 is simply that the gun doesn't have a selector plate in the common sense of the word.

Crunch in relation to your post - the trigger master would fix this permanently because high current is no longer diverted through the switching assembly but through the FET unit only and an extremely small current goes through your contacts on the trigger unit - simple yet expensive permanent fix but worth it in my opinion - either that or ur gonna have to clean ur contacts every little while :P

Like i said it may not help everyone but if ur cut off lever looks good then try this as well

HOPE THIS HELPS!!!!

[Corleone]

You guys are crazy to go with a lipo anywhere over 7.4V! After adding a home-made mosfet, I've tested both a conventional 8.4V NI-MH, and a 7.4V lipo on the P90. It should be more than enough, unless you wanna empty your magazine in a matter of seconds As already mentioned, a mosfet unit should fix the whole problem, and it doesn't need to be as expensive as the trigger master. I think I only spent a few $ per mosfet unit I made. Try it out yourself and save the $$ for other things: http://www.airsoftmechanics.com/home...nt/view/23/26/
While the trigger terminals will burn down eventually (without a mosfet that is), you're greatly accelerating the speed of it's deterioration with that kind of current.

Also, don't go back to your stock wiring Thicker cables can give you a higher ROF, and the stock cables will prolly get really warm with a 11.1 lipo. Of course 14AWG might be a little overkill, but it's better with too thick, than too thin.