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Army R85 Semi Auto Firing Problem


simonmc

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A problem has developed with my R85. In semi auto when I pull the trigger the first shot half cycles the motor and the second time I pull the trigger it fires out 2 bb's. Then the next time it repeats. Half cycle then 2 bb's and so on.

 

Any ideas what's going on here and how it can be solved.

 

Simon

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Are you holding the trigger fully back until it's completed the pre-cocking cycle?

 

Double feeding is usually down to a damaged or worn hop rubber.

 

 

Trigger is being held fully back. The first shot actually feels as if there is not a full cycle. Like it stops half way. Second shot feels normal but throws out 2 BB's.

 

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Doc, its not double feeding. My G&G SA80 started doing the same thing.

 

basically, you fully pull the trigger, it then winds back, but doesn't fire. You then pull the trigger fully again, and it fires the previous BB, cycles again and then fires the next BB. Rinse and repeat for each cycle. Regular as clockwork. Its not occasional, its every time. Full auto works as it should.

 

Its odd, but great for double tapping as long as you can remember to pull the trigger to get it to the 'pre-cocked' stage.

 

I think its something to do with the single shot selector getting stuck or some such, or a bit of wear in the tappet.

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...the second time I pull the trigger it fires out 2 bb's. Then the next time it repeats. Half cycle then 2 bb's and so on...

Sorry, but that's a perfect description of double feeding :P

So it's giving a 2-shot burst?

Only things I can think of are a worn cut-off lever, or possibly burnt trigger contacts which may be holding together long enough (basically spot-welding themselves together momentarily) to complete a second cycle before the cut-off can seperate them.

When it stops cycling, does it end up in the pre-cocked condition every time/sometimes/not at all?

The tappet (plate) only controls the feeding of the BBs, as in any AEG, so it couldn't cause this.

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When it stops cycling, does it end up in the pre-cocked condition every time/sometimes/not at all?

 

It is every single time. First pull of the trigger half cycle with nothing firing. Second pull a full cycle and 2 bb's fire. Regular as clock work.

 

Full auto works like a dream though :)

 

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The G&G and Army SA80's are timed to finish the cycle in a cocked position. That means, the cut-off lever cuts the power so that the piston remains back. When starting from a "relaxed" (piston forward) position, the first trigger pull will only cock the piston.

 

The "cocked -> two cycles -> cocked -> two cycles" stems from the gears not stopping soon enough when the power is cut. From the relaxed position, the gears don't reach full speed before the power is cut. That's because the motor is working to cock the spring and bring the mass of the gears into motion at the same time. When the cycle starts from the cocked position, the gears accelerate without touching the piston (because there's the smooth part of the sector gear), and they will continue to turn just far enough to release the piston, after the power is cut. That's why every other shot is different. To simplify as a list, this is what happens:

 

1. Trigger is pulled. Gears start to turn and cock the piston at the same time. The cut-off lever cuts the power, the gears stop and the piston remains cocked. No shot is fired.

2. Trigger is pulled again. The piston is released (1st shot), and the gears accelerate freely. The sector gear engages the piston again, but the gears already have gathered inertia. The piston is cocked again and the cut-off lever cuts the power, but now the gears turn too far and the piston is released (2nd shot).

3. Back to 1.

 

Your problem can be fixed by using a less powerful battery, or adding a MOSFET with a brake-feature.

 

Do NOT tighten the shimming. (Really, I've seen that suggestion one time.)

 

-Sale

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Once again, Sale's got the Gen.

 

Its not technically a double feed, because there is still only one BB per cycle of the piston, as opposed to your more traditional 2 BB's in one cycle.

It is like a 2 round burst, but obviously due to the pre-cocked feature, it occurs on just one trigger pull, then you get a ghost pull.

 

I wonder whether the battery has something to do with it. My G&G one which did this was modified to run on a standard 16 tooth piston (with a spacer) but used the original sector gear (modified to suit the piston). I was then running it on a 9.6v battery. Took a long time for it to happen though. Ran fine for many months prior to this occurring.

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...the second time I pull the trigger it fires out 2 bb's. Then the next time it repeats. Half cycle then 2 bb's and so on...

 

...Second pull a full cycle and 2 bb's fire. Regular as clock work...

 

simonmc, Can you clarify this please.

Both those descriptions (to me at least) are of classic double-feeding ~ 2 BBs being fed and fired in only one cycle of the 'box.

Is it that (are you getting 2 BBs fired but with just one 'bang' (for want of a better word) from the box?), or is it cycling twice with just one pull of the trigger ?

 

If it's cycling twice with one pull of the trigger, then the passive braking contacts may have become dirty or pitted enough to not be operating, or the wire may have become disconnected.

I'd be very surprised though, if there was enough inertia in the geartrain to wind the piston enough for a second shot, after the cut-off had activated.

Is the gearbox still standard?

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(1)

Regarding finishing the cycle in a "cocked position", if you fire with the cylinder assembly removed, would you see the last one or two teeth of the sector gear exposed? For my G&G, it looks like all those gears that mesh with the rack gear return inside the gear box.

 

(2)

When my G&G was brand new, I wore out the first few teeth (opposite end to the piston head) of the rack gear on the first day out. At the same time, the motor depth was not set properly by the manufacturer (gun became an electric drill mid fight). On the replacement piston, the last few teeth before the metal tooth are showing signs of wearing. Anyone has any idea the cause of this strange behaviour? (I use a 7.4 20C 2200mAh LiPo)

 

(3)

When I fire semi-auto slowly, I've not problem. If I fire semi-in quick succession, the G&G jams. Sometimes can be freed by firing a burst in auto, sometimes require a spring release to free. Can this be cured?

 

Erik.

 

 

 

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simonmc, Can you clarify this please.

Both those descriptions (to me at least) are of classic double-feeding ~ 2 BBs being fed and fired in only one cycle of the 'box.

Is it that (are you getting 2 BBs fired but with just one 'bang' (for want of a better word) from the box?), or is it cycling twice with just one pull of the trigger ?

 

If it's cycling twice with one pull of the trigger, then the passive braking contacts may have become dirty or pitted enough to not be operating, or the wire may have become disconnected.

I'd be very surprised though, if there was enough inertia in the geartrain to wind the piston enough for a second shot, after the cut-off had activated.

Is the gearbox still standard?

Well I'm not simonmc, but the gearbox is cycling twice, no double-feeding involved. I've seen this before on other guns when the contacts were fine for sure, and the cut-off lever was working properly. It is indeed surprising how much inertia the motor and gears have. This is why the Tokyo Marui PSG-1 and G&G L85 have a short-circuit braking system built into the trigger mech.

 

It is possible that the original short-circuit braking system has corroded contacts and is not working anymore.

 

(1)

Regarding finishing the cycle in a "cocked position", if you fire with the cylinder assembly removed, would you see the last one or two teeth of the sector gear exposed? For my G&G, it looks like all those gears that mesh with the rack gear return inside the gear box.

With the cylinder assy removed, the piston and spring are not slowing the gears down, so it is possible that they would turn a bit further than they are supposed to. But with the braking-circuit working as it's supposed to, the gears should stop quickly.

 

It's been a while since I touched a G&G L85 and I don't like pulling the trigger with parts of the mechanism removed, but if the gears don't slow down quickly but vanish into the gearbox instead, that could mean there's a problem. Please note that I'm only speculating here.

 

(2)

When my G&G was brand new, I wore out the first few teeth (opposite end to the piston head) of the rack gear on the first day out. At the same time, the motor depth was not set properly by the manufacturer (gun became an electric drill mid fight). On the replacement piston, the last few teeth before the metal tooth are showing signs of wearing. Anyone has any idea the cause of this strange behaviour? (I use a 7.4 20C 2200mAh LiPo)

How about the last tooth on the sector gear, and the metal tooth insert on the piston?

 

Personally I'd put a 10 mm bushing between the piston head and a regular AEG piston, and cut off the three first teeth off the G&G sector gear to avoid piston timing problems. That, or a stronger spring to ensure that the piston is positively forward before that pesky little sector gear comes around again. You do have the second piston tooth removed or at least lowered, do you?

 

(3)

When I fire semi-auto slowly, I've not problem. If I fire semi-in quick succession, the G&G jams. Sometimes can be freed by firing a burst in auto, sometimes require a spring release to free. Can this be cured?

A common AEG-thing, but pre-cocking models seem to be more prone to this. When you shoot quickly, you actually release the trigger before the cut-off lever has done its thing, so the power is cut off prematurely. The gears stop at the point where they would normally actuate the cut-off lever, and the lever remains half-way actuated, disabling semi. Turning the selector to full auto pivots the cut-off lever out of the way, clearing the stoppage.

 

You need to keep the trigger pulled until the cycle has completed. If you don't want to slow down your trigger finger, speed up the mechanism instead.

 

-Sale

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Well I'm not simonmc, but the gearbox is cycling twice, no double-feeding involved...

I know, that's why I'm asking him for clarification :P

 

It is every single time. First pull of the trigger half cycle with nothing firing. Second pull a full cycle and 2 bb's fire...

I still say that's desribing a double feed...

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Re-assembled the L85 I have in at the moment (in for new piston).

 

I'd previously done the 16-tooth piston mod on it, using my extended piston head idea.

Then I had it back to install a MOSFET and fully re-wire it.

The only problem it had had previously was a tendency to not fire in Auto if you pulled the trigger back hard.

Semi was fine, never missed a shot, but switch to auto and pull the trigger right back and it wouldn't fire. Let the trigger move ever-so-slightly forward and it'd fire, then would be fine no matter what you did with the trigger, until you went back to semi (or safe).

 

Anyway, I fitted the new piston (Marui, as before), did Stealth's trigger bar tweak, and reassembled it.

B##ger me if it isn't now doing exactly what we've been discussing here <_< .

I'm annoyed :angry: , but I had to laugh as well :D

 

It's cycling twice, after the initial pre-cocking, no question (I tried it with the upper body off).

Then, after a few shots (10-12) it just starts cycling like a 'normal' AEG, single shots, no pre-cocking at all.

 

I'm wondering if the higher ROF is overwhelming the passive braking?

 

By the way Stealth, I'm in no way insinuating that the trigger bar tweak caused it, if anything, that would cause it to stop sooner, rather than later.

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How about the last tooth on the sector gear, and the metal tooth insert on the piston?

 

No noticeable wear. Metal parts did not look shiny.

 

Personally I'd put a 10 mm bushing between the piston head and a regular AEG piston, and cut off the three first teeth off the G&G sector gear to avoid piston timing problems. That, or a stronger spring to ensure that the piston is positively forward before that pesky little sector gear comes around again. You do have the second piston tooth removed or at least lowered, do you?

 

I modified my AA with the Redwolf kit. The spacer is thinner than 10mm. I dremelled the first 3 teeth of the stock XTY gear instead of using the Redwolf sector gear. The Redwolf sector gear is made of really nasty aluminum. I still couldn't fire semi in rapid succession without jamming.

 

On the other hand, my Star has absolutely no problem in rapid firing in semi. The micro-switch trigger turns out to be a really good idea.

 

Erik.

 

 

 

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You have Overspin. A soup to nuts definition of what Sale stated. (I answer this question a lot...)

 

Overspin - AEG's were engineered to be operated with batteries with discharge rates of 10-15 amps. Most batteries with high discharge rates of 30-35 amps or greater have the power to compress big springs and increase rate-of-fire. Unfortunately, a side effect is Overspin. Overspin occurs when the flow of electrons is cut from the trigger, but the residual electrons continue to spin the motor due to the high discharge rate and torque of the motor. This leaves the piston in a random position of being "half cocked", and the nozzle sometimes retracted. On Thompson V6 boxes, semi-auto results in 2 and even 3 round bursts. To end the effects of Overspin, a MOSFET trigger with ACTIVE BRAKING is installed. The braking will immediately cease the flow of electrons by sending the residual electrons to the negative side of the battery. This can also be accomplished with a SPDT auto relay. Which is much too large to install into most AEG's. But it can be done on the larger support guns builds.

 

Is Overspin harmful? Not really. Unless you have a very weak spring and the piston is 3/4 of the way back.

 

Is there another way to stop Overspin besides a MOSFET or SPDT relay? Yes. Downgrade your battery. Or get a low torque motor.

 

What's a low torque motor? Spin the pinion head of your motor. The easier it is to spin the pinion head, the lower the torque. You can also tell by the magnetic field generated by the motor.

 

///ed///

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That's what I was getting at when I said;

...I'm wondering if the higher ROF is overwhelming the passive braking?...

I'm pretty sure that's what it is now.

I can make it stop at different positions in the cycle by adjusting the position of the passive braking contact strip, (e.g. moving it forward stops it sooner) but I can't get it consistent, or where I want it.

The owner says he'll be quite happy to lose the pre-cocking (there's negligeable delay anyway with the re-wire and MOSFET) as long as it's reliably firing semi.

 

As to the spacer sizing.

The heads I make are 25mm in length (using a Marui piston), which includes the Angle of Engagement adjustment.

When I make spacers, they're around 15-16mm (depending on what piston and head are used), again, that includes the AoE adjustment.

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Sorted :P

Had to modify the passive braking contact strip so that it makes contact the instant the cut-off is activated.

 

Straightened the original contact strip and soldered on a small section cut from an old selector plate strip.

L85passivebrakefix.jpg

It's only a matter of a millimeter or so difference in position but it works perfectly now, pre-cocking is spot on.

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I'll try.

It's all hidden by the passive braking contact mounting plate when it's assembled, but I'll take a few more, and maybe do a diagram with some dimensions if that'll help?

It needed a bit of trial and error, and the use of a multi-meter, to check that the trigger block passive-braking contact point was breaking contact with the passive-braking contact plate before the trigger contact plate touched the other trigger contact (it's in contact with the other one constantly, for the passive-braking circuit).

You might need to read that last sentence a few times... :huh:

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OK.

This is how the trigger contact assembly looks now.

At the top is the cover with the attached passive braking contact plate (which is in a fixed position) ~ PBc2.

Imagine it's hinged along the yellow line, to put it back in place the top edge flips down and ends up at the bottom, with PBc2 contacting PBc1.

PBc1 is the passive braking contact which is connected (electrically and physically) to the Trigger contact block, Tc1.

When the trigger is pulled, the trigger bar pushes the whole trigger block assembly forward (to the right in this picture).

Tc is one of the trigger contact strips, and is always in contact with Tc1, but does not touch Tc2.

Tc2 is the other trigger contact strip, and is contacted by Tc1 when the trigger is pulled (just before the trigger block is fully forward).

L85trigger2.jpg

PBc1 must break contact with PBc2 before Tc1 contacts Tc2.

When the cut-off activates (in semi), the spring pushes the trigger block rearwards (to the left), and when PBc1 contacts PBc2, the motor goes into passive braking mode.

Again, Tc1 must break contact with Tc2 before PBc1 contacts PBc2.

The shorter the delay between those two states, the sooner the cycle will be halted.

As I mentioned before, it'll take a bit of tweaking and trial and error to get the pre-cocking working.

Or, you could just get it to fire reliably in semi, in the same way as a 'normal' AEG does, your choice.

This is a crude schematic of the contacts' relative positions.

Top is with the trigger relaxed, below is with the trigger pulled, with a plan view under each.

L85trigger2schem.jpg

 

Hope that all makes sense, I can only proof-read it twice myself before my eyes start to glaze over... :wide-eyed::wacko:

 

Just need to see if it holds up for some skirmishing now, the owner will be finding out in about 10 hours time...

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