Forward Assist for semi-only guns.

[Gandolf]

In New Zealand and Germany you can't have full auto airsoft guns    So they have to modify their guns in some way to fire in semi-only and they can't be converted to full auto or the Federalies take you out and hang you or something.  Then there are semi-only factory guns like the SVD Dragunovs.

The problem is that dead spot in the Semi cycle...  We heard of it with the Real Sword problem:

http://forums.airsoftmechanics.com/index.php?topic=2214.0

If your gun stops on the trigger dead spot you can't get the SOB out!!  You can't just go to full auto to clear it.  You have to disassemble the gun or get to the motor terminals with and extra battery to kick it over.  

So Jon from NZ thought we should make a nice fix for this since we are all like geniuses and stuff  

You can't just add a trigger bypass switch.  That could be used to fire the gun more than once    Not even a battery terminal out from the motor to kick it since that would be full-auto too...  Those laws may seem to be very tight to us.  But for the folks that live there, these are pretty tight too!!


Note - If you look very close, you will see that this noose has been glue up to make it very difficult to actually use.  Now that's total safety

So my first great guess is a little poly fuse in series with a switch.  The poly fuse would kick out very fast but provide the critical bump to the motor to get it past the dead spot.  I am going to try DigiKey's # 526PB-ND switch in series with one (or more as needed) # 507-1512-1-ND poly fuses.  Less than $3.00 of parts there (before shipping and taxes)    The problem is finding the perfect poly fuse combination and then finding a little PCB to mount it.  If it works it will be super cool!!  You only need like #20 or #24 wire since the power is so low.

Me and the Amigos are thinking of ways to modify the computer Cheetah, Bravo (3One), and TM-III things to do it too.  But many folks are not running MOSFETs let alone the computer ones (many are though).  So it would be nice to have an independent "universal" thing that could bump the motor no matter what switching you have.

I was thinking of electronic things with 555 timers, FETs and all that.  In the end you might as well just use a little cheap ATTINY85 computer chip.  This is what I came up with:



http://extreme-fire.com/Engineering-Information/ForwardAssist.jpg

A very cool do anything blowup/failure proof solution!!!    But that thing would cost folks like $50 (maybe $40) retail      If it ever becomes real, I will call it the "Lamborghini" forward assist (maybe just 'Lambo' to avoid trademark problems). But it would be no match for the switch and poly fuse version cost wise if that can be made to work.

I ordered up some stuff to test.  We'll see where it goes

Terry

[skag187]

I totally support this idea!!
the semi auto "dead spot" is truly evil, but an unfortunate by-product of the AEG design

[kiwi_mat]

This is an interesting idea, there has been some discussion about "unjamming" our guns of late, and some people have been doing some really stupid things that would be viewed as illegal..

My gun on the other hand, after using11.1v lipo and sw-ab-long didn't jam very often, but these days I have problems with the cutoff lever ruining the trigger by nibbling out the plastic.

I have come up with a concept, for adding a small sensor and cpu board to the gun to try and make it work without the cutoff lever and programmed to only shoot once, but complete the cycle any time..

The basics being a "Baby Oranguatan" robot controller, where I use the motor output to drive the sw-ab-long, a input is on the trigger switch and another is connected to a reflectance sensor which will fit on the top end of the trigger housing to sense a black line on my white tappet plate..

http://www.pololu.com/catalog/product/1302
http://www.pololu.com/catalog/product/959

This is going to be experimental, but I have high hopes on the concept, I can do all the programming myself as well as the hardware stuff. I was also thinking of adding a microswitch to the magwell so that the gun wont fire when there is no mag..

This is a winter project for me. (winter is here now)..

I also have a project to make our club a simulated bomb using the above controller, a LCD display and a noisey pezo.

I would imagine that in the future if it works, the sensor and concept would work on the SW-Lion, but I wouldnt be able to afford that at the moment..

Mat.

BTW for those that dont know, I am in NZ too..

[Gandolf]

Hi,

I just got the DK# 507-1512-1-ND poly fuses and this is looking good!!!  That fuse is still too big, but it is doing the job.  So I think we have a very simple solution at hand!

And just as I was typing that...    The thing went up in flames!!!!    Smoke fire!!!  Cough cough...  Jump up and disable the smoke detectors...

Magically, the remains of the poly fuse fell into a plate on the floor...  It might have been a mechanical issue...  Or, it won't work...

Stay tuned........

UPDATE - It's all cool  

I had just soldered big wires to the bare fuse and they were hanging and stressing the terminals on the little fuse.  When the fused fired and heated, the poly got soft and the terminal gave away under the stress.  It shorted over to the opposing plate and it all fried.



This would NOT be an issue if it were properly mounted on a PCB...  So it is all still fine  I had sort of forgotten how much smoke poly can make    But it is pretty benign...

Here is the current pulse it was giving before it burned up (in fact, I think that WAS when it failed):



Too big, but that is easy to fix

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=507-1508-1-ND

 

But I must find a PCB small enough to mount it right...

[kiwi_mat]

Just having a look at the fuze, I am no expert, how does the trip time change with different current inputs.. I noticed its time to trip is 1 second, which i would say is far too long - it means that the gun would be capable of shooting multiple projectiles (bad)..

[Gandolf]

The trip time for those fuses depends on the actual current.  The more current, the faster they trip.  Here is a more clear graph for the SW-AB-LONG's poly fuses.

http://extreme-fire.com/Background/SW-AB-LONG-FuseTripTime.jpg

I will order the new fuses tonight so we will see how they work.

[Gandolf]

Hi,

I got the new poly fuses:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=507-1508-1-ND

They work great!  I soldered it to a scrap PC board and a switch:



The poly fuse in the little green thing in the bottom center of the circuit board.  The board is 20X too big but it is all I could find in ten seconds    Note that the fuse MUST be mounted on a PC board or it will burn up as shown in the post before.  I need to test it a lot more, but once mounted the fuse seems perfectly reliable.

Here are the 8.4 and 12 volt bumps it gives:





It will not fire the gun.  As the gear train winds up the force is easily able to overpower the fuse before the gun can even get near firing.  However, when the gun is in the dead spot (practically no spring force on the gears), it can easily wind past the dead spot.

So it seems perfect!!!  

I am trying to upload a YouTube video but the tube is being a boob right now...  I will update this once it is working.

LOL...  The toob is sucking bad gas this night...  So we go the the motion for a vid that only has 10% of the quality.  But it is fine

http://www.dailymotion.com/video/xdkjt1_aeg-forward-assist_tech

Gandolf

[kiwi_mat]

Looks good, would we be able to use just small bit of vero board with the polyfuze?


I have had some success today driving cutoff via the controller board and the reflectance sensor looking at the tappet plate, unfortunatly the tappet returns to rest before the piston would release from the sector gear, so thats not a good thing to look at a reflection off, atleast I know the reflectance sensor is fast enough. I think it might be better to look at the sector gear as there is room between it and the top of the gearbox shell.. (or maybe a small 4 mm hole) and a disk of white/black..

[Gandolf]

Looks good, would we be able to use just small bit of vero board with the polyfuze?

Sure!!  When poly fuses fire at like 150C.  They get very hot and "plastic" so being mounted on a solid epoxy PCB for high temps is very cool  In fact, You need to put them on a pcb...  But "any" PCB is just fine.

[salamander]

It will not fire the gun.  As the gear train winds up the force is easily able to overpower the fuse before the gun can even get near firing.  However, when the gun is in the dead spot (practically no spring force on the gears), it can easily wind past the dead spot.

So it seems perfect!!!  

I am trying to upload a YouTube video but the tube is being a boob right now...  I will update this once it is working.

LOL...  The toob is sucking bad gas this night...  So we go the the motion for a vid that only has 10% of the quality.  But it is fine

http://www.dailymotion.com/video/xdkjt1_aeg-forward-assist_tech

Gandolf

Iam glad to see it working, very nice, simple, yet very effective solution!

[Stickman]

Thanks for coming up with this solution for me. i have passed it on to ASNZ now, i would like to order in a couple to build into a gun that we can use to demonstrate to the right people.
this solution is pretty much perfect for us here in NZ.

[kiwi_mat]

I was thinking about guns with mosfets installed, for this to work we would have to connect to the switched motor wire - in most cases the negative.. any problems there?

[Gandolf]

You can just wire it across the MOSFET (battery and motor negative).  The fuse does not care about polarity or anything.

[Stickman]

so it still shuts off the same way? because of the draw threw the wire?

[Gandolf]

so it still shuts off the same way? because of the draw threw the wire?

I am not sure exactly what you mean but the unit would do the same and act the same with a MOSFET or a conventional trigger switch.


I have the stuff on order to make them now.  I just got the full board panels and I will just them out on the band saw:



I am trying to figure out the costs:



The column in the far right is near the retail cost.  If they want a switch too, that one is pretty pricey, but everything else is cheap.  You could just have two small screws heads and a penny for the switch too.

If they want everything all wired up then it would be about $15.00 +$10.00 Postage to NZ.

If they want just all the bare parts then it would be $10.00 +$10.00 Postage to NZ.

If they want just fuse board with wires attached then it would be $5.00 +$5.00 Postage to NZ.

Of course, the problem is the post office is making all the money   It would be far better to just send the parts to NZ and have someone there do all the work and distribute them to the folks there.  If anyone in New Zealand or Germany is interested let me know.

Gandolf