Supporters Ian_Gere Posted August 16, 2012 Supporters Share Posted August 16, 2012 Background OK so I've been making a few mods to my AK over the last couple of days, one of which - adding a mosfet, has meant drilling holes in the faux gas block, filing down bits of the receiver, and a lot of fiddling with / changing the electrics. This is because there isn't much room for wiring, particularly in the faux gas block where the battery connector and any extra battery wire has to fit. Nonetheless I had to work out a way to run wires through it, with connectors on, so that the mosfet can reside in the hand guard, yet I can still break the gun down without having to disassemble the whole front end every time I want to get at the gearbox. Thus I also had to move the fuse carrier forward to make room. There were a number of trials and errors before I got it sorted. The Problem Another mod is a swap to what I've been told are Prometheus gears (they're 2nd hand without packaging and I don't know what they should look like), The gears in the bottom left corner. which is necessary because, from the two sets of CYMA gears I have, the spur gears are missing one and two teeth respectively (strangely enough, not the teeth that connect with the piston, the other ones {any ideas about that would be appreciated}). I also had to swap over the air nozzle because I'd had problems with the upgrade that was in there, so I did the whole gearbox stuff first, oh, and putting up that pic reminds me, I was swapping from bushings to Kanzen bearings too. I paid a lot of attention to properly shimming the new gears. I've read that shims should make the gears fit tightly enough that there's as little side-to-side movement in them as possible whilst they still spin easily when they're on their own in the gearbox shell. That then is what I did. During the trial and errors I mentioned above, I had to connect up the battery and test that the cable and mosfet were working several times; naturally setting up the mosfet meant a whole bunch of test firing on full auto to tune the burst function, oh, and I had to also fire the gun with a mag in place, to check that the air nozzle swap had cured the feed problem I was having, and again, since I have 4 options available and I also tried one of them with a different spur gear to see if the tappet plate movement was at fault, that took some trial and error. My point here is that I fired the poxy thing with the new gears in place quite a bit and the only thing I changed once they were in and I'd disproved the tappet plate idea was the shims. It turned out that a set up which seemed right with just the gears was a fraction too tight once everything else was fitted and once I began addressing this issue, it got down to individual gears needing a bit more or less on one side or the other (I suppose I got anal about it). So, I finally had a gearbox that I was happy with (actually I swapped the full metal piston and piston head {on the right of that pic} for a drilled aluminium alloy piston, polycarbonate head and rubber pad against the cylinder head {top middle above} ), a wiring set up that not only worked but also allowed the gun to be reassembled, and a mosfet tuned to bursts of three. I assembled the gun and after a few test shots, the gearbox jammed. I was horrified, but in a "I know what that is" sinking feeling kinda way, because I assumed that a tooth or two had come off a gear and jammed the box up. Mais non mes mechants, there was nothing wrong with any of the gears and no foreign objects in there either; I took it apart gingerly too so I would have noticed if anything had slipped out of place... I put it back together making absolutely sure that everything was exactly in place and... it bloody happened again! I've just deshimmed each of the gears a bit to make it loose (too loose by what I thought was the standard to go by) and it is firing fine. The Head-Scratcher During all the test firing, after the gearbox was first set up, it didn't jam. The only thing that changed was slowly making the gears generally looser, then loosening them further, so far seems to have cured it... What do you say, AF-UK? UPDATE It's 'kin jammed again... grrrrrrrrrrr! Link to comment Share on other sites More sharing options...
Supporters Ian_Gere Posted August 17, 2012 Author Supporters Share Posted August 17, 2012 Panic over. It's the 'kin mosfet! Now that really pisses me off! I bought it from someone on here too, grrrrrrr! Marco from this thread... Wish me luck in my quest for a refund! Ooooooh, I'm so pissed off! I've totally changed my wiring to accommodate the bloody thing and now I'll have to swap over connectors and remove various bits of wire to make it work as it was. OOOOOOOOOOOOOOOOOOOOOOOoooooooooooooooooooooooooooooh, I'm annoyed! Link to comment Share on other sites More sharing options...
Supporters Airsoft-Ed Posted August 17, 2012 Supporters Share Posted August 17, 2012 How was the mosfet causing a lock up? Was it breaking the circuit prematurely or was it obstructing the gears? The other day when faffing with my M4 I found that tightening the rear gearbox screws too much can some times restrict the movement of the AR latch, making it stiff. So it tends to cling on when it shouldn't so the box locks up. I'd have suggested that be your problem if you hadn't said the mosfet was the cause. I think they seem like more hassle than they're worth tbh. Link to comment Share on other sites More sharing options...
Supporters Ian_Gere Posted August 17, 2012 Author Supporters Share Posted August 17, 2012 It was working fine - semi-auto = 1 shot / full-auto = tune it with a little screw from no shots to a burst of 7 - I settled on 3 But after a while it just didn't fire. There was a slight click from the gearbox so I thought it was something jamming it. Then after loads of shim swaps and then changing to Systema gears (for Spur & Sector but the Bevel wouldn't fit so I used a Prometheus one) and it happened again, I got suspicious, so I tried it immediately bypassing the mosfet and, lo and behold, it worked perfectly! I think it was not putting out enough voltage to fire, just enough to tension the gears against the spring making the click - basically the same as with the screw turned all the way down, so I suppose the semi-conductor part must be unstable. I really like the idea of burst firing. If you keep your finger on the trigger after the burst for a second it goes to full-auto anyway, but I was looking forward to firing a series of bursts at moving targets, because I could pull the trigger again instead of waiting. Apart from saving BB's I think it would make my shooting more accurate. I thought you were well up for the ASCU? Link to comment Share on other sites More sharing options...
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