P90TR Full Electronics, MOSFET, Active Breaking, Low Ammo Indication, LiPO + PCB

[WolfDragon]

I posted this on another forum but seeing the amount of traffic this one gets I figured I might as well throw it out over here too since there are probably a lot of curious people here as well.

I hope I am not breaking any rules as this is my first post and it is going to contain links to an external site.

The site is my own, which though some sections still need work, the sections pertinent to this discussion are more or less complete for now until I make something new or feel motivated to publish other things I have worked on.

For an introduction, I am an Aerospace Engineer with a heavy background in Electrical and Mechanical Engineering. While I am still relatively new to airsoft, electronics are not new.

Now for the good part:

My P90TR has every possible electronic doodad I can cram into it without running a small CPU to do things like 3 shot burst. The features it has: MOSFET trigger, Active Breaking of the motor, Low Ammo Indication, LiPO batteries, and overdischarge protection of the LiPO cells. Now you are probably thinking that the low ammo indication is the only new creative thing in the AEG but... all these systems are tied together, so much so that the LiPO overdischarge protection gives an indication and locks out the trigger so the gun can't fire, draw power from low-low cells, and put me out of 50USD for another battery pack.

I offer my information and schematics with no strings attached, the system is tested and is 100% working.

If you want to see what I have done, http://www.projectwolfdragon.com/Toys/Toys.htm

There is a link on that page with a pdf of my schematic, the MOSFET Trigger is a very common design with some added protection and noise reduction for the rest of the components.

If anyone has questions, don't hesitate to ask, I know the land of devices that run on magical blue smoke can be frustrating, especially if you manage to release the magical blue smoke from the parts.

If you are feeling nosy, the projects section (click the banner link at the yop of the page) of my website has some other fun things I have made. It is a section that I still have content to upload, I just haven't had enough time to do it.

[ILLusion]

Very enjoyable and useful info. Good job.

[MadMax]

Thanks for the Lipo circuit. I've been meaning to get around to that for some time, but have been pretty busy with other projects.

If you haven't already, take a peek at:

http://unconventional-airsoft.com/
http://forums.airsoftmechanics.com/index.php?board=2.0

DonP is a member here who really enjoys general hacking. He tinkers with electrical and mechanical upgrades.

There's a guy on AM who goes by Gandalf. He and many others have been doing some pretty interesting work with microprocessor controlled AEGs. They're chasing the holy grail of drop in mechbox cycle counting to put in a counted 3rnd burst and other interesting electronic features.

Several months ago we went thorough a bizzare but ultimately dead ended exploration of a high voltage Lentz effect electromagnetic AEG. Not much traffic there, but there is an unusually high concentration of electro enthusiasts there.

[MadMax]

oops, nevermind. I note you posted on AM already.

[WolfDragon]

Originally Posted by MadMax

Thanks for the Lipo circuit. I've been meaning to get around to that for some time, but have been pretty busy with other projects.

Yes the LiPO PCB was my baby for this upgrade (I finally got to use an OP-AMP for something other than audio), after I switched over to the mosfets I realized that the 8.4 1500mah nimh's I had were just barely enough to turn the gun over at the rate it wanted to go. So I knew LiPO's were the way to fix that but if you drain them below 2.7v (I designed to 3.0V for a good margin) you get to buy a new lipo pack.

If of course you don't want to use the LiPO PCB but you do want to use the mosfet circuit, just bridge Ta and Tb.

For those of you wondering why only 2 cells (7.4v pack): The packs I have can source 20amps continuously, which is what my AEG is fused at, the motors are meant to see anywhere form 7.4 to 8.6 volt nimh and nicad packs, running higher voltages and packs that only give like 2500 or 3000 mah at low C rates is only cheating the physics of the batteries (to give the motor the current it need to run, not the voltage) and hammering your motor's brushes to death.

Believe me, 7.4v 20A source is plenty, I'm on a magnum motor with highspeed prometheus gears pulling a 140 spring - at 25+ rounds per second.

IF you really want to use this circuit and 3 Lipo cell packs (11.1V) msg me, I'll update the PCB with another difference amplifier and comparator.

[El Cactus Loco]

wow. SKILLZ!

[ProbeJax]

Oh wow, a low ammo indicator. Gotta try that out.

[ProbeJax]

Going to try out the ammo indicator. Gotta gather the materials. Did you make your own circuit board for this?

[WolfDragon]

yes but you can get away with it fairly easily if all you want is a low ammo indicator

note, i am assuming you have a p90 with a hicap mag, I'm sure with work you can get another mag/aeg to do this, but i know the P90 hicap works well

I used a magnetic reed switch of about 20 AT (ampere turns) i would suggest going higher as i had to shock proof the switch to prevent false actuation

the magnet, you need a prettey powerful magnet, i used a chunk of a neodymium magnet, about 10x10x3 mm in dinension, theres a lot of space in that magazine block where you would line up the reed switch, use a big magnet it will not affect the spring.

as far as circuitry goes, any Set Reset Latch will do, i used and active low one, regardless of if its active low or active high, you will have to wire pull up or pull down resistors as needed

If you would like, PM me and we can work something out, I can make you something with just wires coming off for power and the switches.

Or if you really want to do it yourself, PM me letting me know what your soldering skills are and I can give you digikey (my toystore) part numbers.

[MadMax]

Ever think of using an iron magazine follower? I was once toying with the idea of putting an iron follower into a mag to be detected by a coil wrapped around the hop up tube that pokes into the mag opening. I was thinking of detecting a change in inductance to detect an end of mag condition and cut off the AEG motor.

[WolfDragon]

looking for change in inductance only really works if the magnet or metal is large or fast moving, for an AEG i wanted something fundamental and slow because it would be cheap and easy


if you did something with inductance, you would have a base LRC type of circuit but you would have to tunes it's sensitivity/threshold for each application

not saying it can't be done, but a magnet and a magnetic switch is easier

[MadMax]

The reason I was thinking about a coil is that I couldn't find a reed switch small enough to fit inside a hopup inlet. A circuit which would measure a rise time on an inductance coil might be able to do that.

[WolfDragon]

the only other easy application i could see is with mid or lowcaps because of the bbs being in a fixed channel with a slide

if you replaced the plastic bb pusher with a machined steel one and magnetized it, then put the reed switch inside the magazine at the top so you wouldn't get erroneous indications from the slider passing in the loops at the top, you could get away with it

then its just a matter of having two contacts on your magazine that get connected when you put each new mag in, yes you would have a switch in each one

the one i use from digikey is about 15x2 mm cylinder

I will see about getting my hands on an AK or M something or other magazine but that wont be this week unless someone on this forum sends me one

by all means if u want to give me a new project PM me