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[Dev] In-grip/pouch electric warmers for gas guns

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  • [Dev] In-grip/pouch electric warmers for gas guns

    Hey all, looking for a few opinions from everyone!

    I’m a UK based airsfoter and currently have 3 gas guns, one of which is a classic Maruzen Micro Uzi (the one with the recessed mags), as well as strongly considering getting my hands on a GBBR. As many of you know gas systems and cold do not combine too well, so the obvious solution is to add a small heating element to the mix. So the obvious solution is to add small heaters into the two places that the mags reside in, the pouches and the grips.

    Problem with just adding a heating element and a battery however is the fact that A) battery life would be terrible and B) the common heater the right size heats to up 40deg at 5v. This isn’t ambient temperature as well, but direct application, meaning that the magazines run a risk of over-pressurizing and blowing or sending the fps sky high for the first shot.

    So I found myself in a situation where I was in a pub, having lunch with a bunch of environmental science students who were discussing the more exiting species of lichen, which led to this:



    What you see there is a very basic temperature control system. At the top you can see a heater and thermistor. In the middle you have a voltage comparator and a simple voltage divider circuit, with one end having the thermistor and the other will have the appropriate resistor, which sets the default cut-off point for the heater. At the bottom you have a 3.7v battery, ideally a li-on one, taken from a mobile phone, as they come with protection circuits built in, meaning that charging them is a piece of cake and I don’t need to worry about the usual lipo troubles with charging and discharging. Also, as it’s only 3.7v, it should drop the heater voltage to a max of about 25-30deg, which is a little bit safer than 40 I guess. I am not 100% sure as to what a safe heat is however.



    That’s a more sensible version of the above image, with a charging point. What I am struggling with at the moment is being able to understand how the thermistors actually work. Ideally I’m after a device with a linear or roughly linear relationship of heat to resistance, meaning that I can get the heater to a certain heat measure the resistance of the thermistor and find a resistor of that value. That way I can manually calibrate the cut-off points for each device.

    Also, the other part I am not 100% on is the comparator switch. I know that they are cheap, and usually come with two in one package and compare voltage. But how they work or which one to pick is also a tricky one. I can dig out my op-amp lecture notes, but I think it will be cheaper to buy a prebuilt comparator. Hell, this may not even be the best way to do this, so any input would be much appreciated. All I know I need is something that completes a circuit is one voltage is higher than the other one and runs on as little as 3.7v and if it has some sort of delay built in that would be even better.

    Oh, and for reference on costing and sourcing parts etc, these shops don't sell airsoft bits, are all within forum policy.

    Heaters
    Available in USB heated gloves, pretty much any China-crap store, such as ebay, bestofferbuy.com etc from ~£4 and come in pairs, sometimes even 4 in a set. They also come with nice small bullet connectors and a USB cable that you can use to make the charger.

    Thermistors
    Are the NTC types and are available on ebay

    Comparator
    No clue, all I know, is I need this, a Dedicated voltage comparator chip

    Anyway, hope this helps someone or someone has any advice to help me, even if it’s something mind-numbingly simple, haha

    Apologies, please merge with bottom of post:

    Just saw this website: http://www.brighthub.com/engineering...les/60941.aspx
    Looks perfect for me, available on the bay for 2.20 for 6, I'm sure RS etc would have it for cheaper. Was getting confused by some of the other models which had clock in pins and all sorts -_- Seems to have a voltage range of 2-36V. I may end up needing a quad however so that I can use one to disconnect the heater circuit from the charge loop... Or should I not bother to allow for external batteries etc? bleh, decisions...
    Last edited by Rampage; 11 April, 2011, 14:58. Reason: Op Request

  • #2
    Re: [Dev] In-grip/pouch electric warmers for gas guns

    Judging by the lack of screams of "you crazy, homes" or "You noob, that's not how electronics work", I can only assume I must either be doing something right or building something very boring :P

    I have ran into a bit of a dead end however, to do with the charging system. Am I right in assuming that the mobile phone li-on/li-po protection circuit is a magical force field that will allow people to pump in USB-ish voltages (4v-6v) and enable it to safely charge up to the usual 4.2v? In addition I can only guess that it prevents the cell from falling below 2.whatever volts and manages the trickle charging up to that point? At least that is my understanding of over/under voltage protection.

    I spent most of last night browsing data sheets of various charging chips and have managed find this little beauty, a 5 pin li-on/li-po charge manager which is a reasonable size for a surface mount (through hole charge managers don't seem to exist, grr) and only needs a few 1uF decoupling caps to make it work.

    Question is however, do I need it? My googling only brings up info on unprotected batteries, but nothing on what the basic standards for the protection circuits actually are and if I can rely on them to protect the battery from destroying itself while the heater is on or during the charge.

    Anyway, in an attempt to answer this, under close supervision, I've directly wired the battery to my USB port, out of interest if anything. It may explode, may not even do anything, I dunno. If I learned anything last night, it is that this should technically work.

    We shall see how it goes I guess..

    Comment


    • #3
      Re: [Dev] In-grip/pouch electric warmers for gas guns

      I just put mine on a hot water bottle before a game lol. Fair play to you though!

      WARNING. Post may contain traces of sarcasm. If you do not understand this, I pity your existence.

      Comment


      • #4
        Re: [Dev] In-grip/pouch electric warmers for gas guns

        Great idea.

        Something slick and very portable that say, slips into the pocket of a mag pouch would be the solution though:

        (for example having a sleeve or something that the mag easily slips into thats powered by a bettery in an adjoining mag slot perhaps)

        Comment


        • #5
          Re: [Dev] In-grip/pouch electric warmers for gas guns

          yup, id buy one! cold mags bug the living daylight outta me!!
          sigpic
          Dog Soldiers Airsoft - We hope we give you the shits.

          Comment


          • #6
            Re: [Dev] In-grip/pouch electric warmers for gas guns

            Yeah, the pouch warmers are a lot more simple to make due to the fact that you can afford to use A larger variety of battery solutions, AA even, as like you said, you can just stick it into a dummy mag pouch and be done with it.

            Ideal solution though would be a flat lipo and the control circuit in a waterproof bag within the fabric on the back of the pouch, with a charging port tucked away somewhere, suitably protected from getting wet. No fake pouches, no extra room taken up and all the benefits, can't be bad, eh?

            I've not really been focusing on these too much yet though, as I know that a mag can stay as warm as it likes while in storage, it's in the pistol, where it tends to lose temperature for me. Every time I forget to switch a mag out of my pistol for a warm one for a while, it comes out ice cold, whether it's even been fired or not -_-

            So I'm soldiering on with the grip design for now, which I will be able to make a straight conversion over to pouches or the stand-alone mag wraps which you mentioned, Fitch afterwards. All this fuss with charging etc is really a nice-to-have, as I don't like half-finished designs. I could cop out and just use single-use cells or use a phone cradle charger to do the job, but I just think it's such a bodge...

            As soon as it's all done, I'll make detailed guides on how to make one or if people really want them I could build a few sets and see how it goes, but whatever. I'm know I'm not the first to make something like this, probably won't be the last. It's about time someone documented it though.

            Comment


            • #7
              Re: [Dev] In-grip/pouch electric warmers for gas guns

              Cold mags are most definately a pain in the backside, and this is a potentially very good idea. Whether it would take off or not I dont know, personally I just use one of those reuseable handwarmers from a camping shop. Pop one of those behind my pistol mag pouch and jobs a good 'un, so far my mags have neither exploded or reached a billion FPS and shot the moon down

              Comment


              • #8
                Re: [Dev] In-grip/pouch electric warmers for gas guns

                yea I keep hand warmers with my pistol mags as well, but unfortunately it does mean that the one in the gun will get cold after you've reloaded...

                i had this outrageously stupid idea once and drew up a sketch where essentially after every shot, a tube (external at this point) would guides some of the gas back to the grip panel (1911) into a heat sink, and the gas would be ignited by a spark generated from the moving slide by friction similar to a lighter's flint... so not only you get a nice warm magazine, bit of cool visual explosion, a potentially melted bb, and best of all, a burnt face if the whole thing blows up... but hey, i hvn't felt suicidal enough to build this just yet.

                Comment


                • #9
                  Re: [Dev] In-grip/pouch electric warmers for gas guns

                  Originally posted by blobface View Post
                  yea I keep hand warmers with my pistol mags as well, but unfortunately it does mean that the one in the gun will get cold after you've reloaded...

                  i had this outrageously stupid idea once and drew up a sketch where essentially after every shot, a tube (external at this point) would guides some of the gas back to the grip panel (1911) into a heat sink, and the gas would be ignited by a spark generated from the moving slide by friction similar to a lighter's flint... so not only you get a nice warm magazine, bit of cool visual explosion, a potentially melted bb, and best of all, a burnt face if the whole thing blows up... but hey, i hvn't felt suicidal enough to build this just yet.
                  Maybe leave that idea alone
                  Others till I die

                  Comment


                  • #10
                    Re: [Dev] In-grip/pouch electric warmers for gas guns

                    As you said, the cheapest (by far) heaters that are available are from usb mug heaters. From a little searching on ebay, they are ~2.5W @5V.
                    P=VI, therefore this gives a current of ~500mA. Comparators give a max current output of ~30mA. So you would need some kind of amplifier/buffer thing. Also you have got to be careful with the inductance of the heater, when turning on and off. This will cause an emf spike and possibly break the components (Same if you have a mosfet in your trigger assembly).
                    I therefore propose a mosfet (because they are ‘cool’, pardon the pun) to act as a switch to turn the heater on and off. This will only work if the heater and the thermistor are in very close proximity, that or you can use hunting to make it work, but that means more circuitry.
                    This diagram should make sense:

                    The values are not all calculable without the voltage of the batteries being used, but it’s not too difficult to change them
                    The 10ohm resistor and the 10mH inductor is the heater. There are two diodes to stop the mosfet blowing up and the 10k pot is to vary the temp you want to heat up to.
                    Sorry if this makes no sense, it’s been a long day.
                    I cannot try this theory out till I get back from uni on the 25th but will keep you updated when I try this out.

                    Comment


                    • #11
                      Re: [Dev] In-grip/pouch electric warmers for gas guns

                      Hi Pau1,

                      Very cool, your circuit makes perfect sense and cheers for the heads up on the comparators. I will be using an LM393, though, after reading the datasheet again (and again and again, haha) I was not able to spot where the max current this thing can kick out was? Could you let me know which bit I should be looking at?

                      Also, there is a cheaper alternative to usb heaters though, at least if you are making more than one set of these: Resistance wire! fantastic stuff, and there is a very good website teaching you how to use it here

                      However I fear you may very soon fall into the same development hole I have done, that is if you are also trying to fit the system entirely within a pair of grips. The space constraints mean that there really is no alternative, other than using lipos. And in order to use those, you need to use a decent charger chip and then build a custom under-voltage protection circuit on top of that.

                      Let me post up a recent post I made on Arnies and Airsoft Mechanics on the subject:

                      Hi everyone

                      Quick update on design progress and a big (for me) question actually.

                      I have decided to use a cheap unprotected lipo, as those 'protected' lipos only protect the thing from blowing up, not from being damaged.

                      The charging part is easy, I can just used that 5 pin charging chip I mentioned earlier. It's surface mount, but not ridiculously small, so I should be able to handle it, just tore the circuit for that out of the datasheet.

                      The under-voltage protection is another story however... That has been a royal pain in the ass and I have found literally one example of how to build one.

                      http://www.aaroncake.net/forum/topic.asp?TOPIC_ID=8492 (last pic on there, posted by AudioGuru)

                      It looks ok, but the hysteresis part looks dodgy to me, does it need a diode in there as well as that resistor? If so, which way is the current even meant to be flowing there? Also, what should the resistor value be, if R1 = 470k and R2 = 33k? as those two pair up to make a steady 0.2v at 3.048V or something like that, thus triggering the cut-out then. So lets you use most of the battery's voltage without exploding.

                      Also, is there a better or cheaper way to do this? The LM10 is quite expensive (comparatively speaking) I searched all over the place, but no luck.

                      Only thing I found (well, stumbled across only today actually) is an adjustable voltage regulator, the LM317L what do you reckon, usable? Better alternative?

                      Anyway, here's my most up to date circuit, would really appreciate any help you can offer!



                      Datasheets:

                      MCP73881: http://www.datasheetarchive.com/pdf-...SA-357692.html

                      LM10: http://www.datasheetcatalog.org/data...r/DS005652.PDF

                      P.S. as you can gather, I am not an EE, just someone who'se dabbled in it a little bit. So stupid, glaring errors are there by accident, please do pick me up on them!
                      Btw, nice first post mate :D Stay in touch
                      Last edited by aribos; 20 June, 2011, 12:28.

                      Comment


                      • #12
                        Re: [Dev] In-grip/pouch electric warmers for gas guns

                        So could you mod a holster so that the mag holder was heated ? Guess it would save leaving the spares down my pants and having to grip the handle tight with both hands in an attempt to keep the gun warm on a winters day but what would you do to keep the mag warm in the gun ?

                        Even co2 seams to suffer if you start off loading fast on a cold day
                        sigpic
                        Oh when will I get a decent knights stoner LMG aeg ?

                        P mags up for sale http://forums.zeroin.co.uk/showthrea...encer-200mm-m4

                        Comment


                        • #13
                          Re: [Dev] In-grip/pouch electric warmers for gas guns

                          Of course. Ultimately, all the heater is, is a coil of wire. The circuit board I anticipate being no larger than 5mm high at a size of 50x20mm or so, or whatever the hell I decide to keep it at, will need to see once I finalise the details, then you have the battery, which can be anything really. Find a pouch to store all that in (or just whack it all in behind the holster) and you are good to go

                          For the mag in the gun, the entire thread is about building heated grips, so those detachable grips would be replaced with ones which contain the battery, circuitry and heating elements. If you are a bit creative about it, I am sure you can get the concept to work in any gas gun.

                          Comment


                          • #14
                            Re: [Dev] In-grip/pouch electric warmers for gas guns

                            Bloody gas pistols eh!

                            Had the other problem today- it was too warm. None of my pistols were able to effectively fire and shift their slides. Just too damn hot.

                            I just wish that c02 was more tuneable to get it below site fps thresholds.

                            Comment


                            • #15
                              Re: [Dev] In-grip/pouch electric warmers for gas guns

                              Not sure if it was here or Arnies.

                              Some guy was doing this, and nearly blew the bottom of the mag off....!

                              Comment

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