INTRODUCTION
I got into airsoft almost exactly one year ago. While I suck pretty handily at playing, I seem to have a better aptitude for the tech aspect of things.
I wanted to put together everything that I've learned in the last year into a single project. I had picked up a broken TM G36C off of Craigslist a while back. It was in pieces, but the owner claimed it was all there plus some extras. And at $80, the price was right and satisfied my Japanese predilection.
I'm a few months along on the project and have been taking pictures throughout. I wont lie and pretend like everything worked out perfectly as I've already made some mistakes, but that's how we have to learn sometimes.
I've learned the vast majority of tech knowledge from http://forums.airsoftmechanics.com/. I suggest this site highly.
Nothing I'm attempting in this build is revolutionary, instead it's an attempt at replicating what has been verified to work best. My goals are fairly moderate compared to what is possible. From the onset, I was looking for mid 300s for FPS, and mid 30s for rounds per second keeping with a CQB mindset as a foil to my DMR AUG, while being significantly less expensive than my DMR build. I also wanted to restore the appearance of the gun as it was in pretty poor shape as it had been sitting in a box in his garage for a few years, and had a few years worth of use before that.
START
Right after I first bought it, I gave it a good cleaning and test fit everything together and I placed it next to the rest of my collection.
http://i16.photobucket.com/albums/b46/s ... /Start.jpg
The front inner barrel assembly had been cut up quite a bit to make room for an extra large battery, a ni-cd. I would not be using this dinosaur. One of the nice extras was a Laylax extended hand guard. One of the not-so-nice extras was the front of the inner barrel assembly, where the flash hider screws on to, had snapped off. This was fixed with epoxy and a zip tie. Crude, but effective.
After media blasting the metal exterior bits and repainting them black, and opening the gearbox for an inspection, regrease, and a proper shimming, I took it out to a game and let a friend use it. It held up well, firing a healthy 365 fps with the only internal mod being an M100 spring installed by the previous owner. The large metal piston head spacer was still inside the piston and compressed the spring to a higher output (normally an M100 should shoot around 330fps). Rate of fire however, was a very sad 9 rps with a 8.4v ni-mh.
Also, my rattlecan paintjob was destroyed after only a single game. The rest of the metal components fared as well as the flash hider.
http://i16.photobucket.com/albums/b46/s ... dPaint.jpg
Obviously, it needed to be redone properly.
BODY
I decided on a camo paint job and collected some images that served as inspiration.
http://s16.beta.photobucket.com/user/sp ... nspiration
I didn't want to just spray the whole thing, as that looks a little cheap to me. I disassembled the entire replica and went back to the media blasting cabinet to take all the crap black paint from the metal bits and give a little texture to the plastic body.
After my fiance told me I couldn't cut up her laundry bag to use the mesh netting for that 'snakeskin' look that I wanted, I did the next best thing and cut up an old dishrag that had a nice mesh backing to it. I used Krylon Fusion camo ultraflat paint as I had heard good things about it adhering to plastic.
After cleaning all the plastic pieces in alcohol and allowing them to dry, I painted each piece separately with a base coat of tan. I let that dry for a few days (while it may be dry to the touch quickly, it can take weeks for the paint to dry completely). I then assembled the body together with the exception of the stock and top rail as I wanted those, and the hardware, to stay black.
I placed the washcloth mesh over a small section of the body at a time and randomly applied dark green and dark brown streaks and spots. I sprayed from the top down as I wanted the lower parts to be lighter, emulating the underbelly of a reptile. After letting that dry for a few hours, I was unsatisfied with how tan it still looked, so without the mesh I sprayed more dark green and brown, then letting that dry I placed the mesh back over and did a few light touches of tan. The results of this made me happy.
http://i16.photobucket.com/albums/b46/s ... tClose.jpg
http://i16.photobucket.com/albums/b46/s ... intFit.jpg
Letting this dry for a few weeks touching it as little as possible and it left a nice durable finish that should not chip. To date I haven't taken it to a game, but I'm anticipate some scratching, which is fine as it should break up the outline even more.
You may have noticed the white trades on the left side. This is actually quite simple to do. Because this is a US market gun, the "HK" and "G" and "C" were scraped/burned off before importing. However, the media blasting had revealed that the original casting impressions were still there, showing me a faint outline. Before I painted it, I took a sculpting tool I had laying around and carefully restored the trades, not perfectly, but good enough.
I used a cheap acrylic white paint and a small paintbrush. Don't be sloppy, but paint as close to the lines of the trades as possible, like this:
http://i16.photobucket.com/albums/b46/s ... dies-2.jpg
And with a damp cloth, lightly wipe away the excess paint. Work in small sections and wipe away the excess before it dries. Voilà:
http://i16.photobucket.com/albums/b46/s ... ades-3.jpg
For the metal bits, I researched various coatings, but it seems the zinc-alloy that TM uses for their castings is pretty difficult to apply a coating to without special equipment. So I decided to go with an epoxy paint specifically designed for airplane propellers as I figured that would be as tough and cost effective as anything. http://www.skygeek.com/a150.html. I then put everything aside for a few weeks to fully cure and dry.
With the paint complete, I went to the local hardware store to replace the original nuts and bolts that were badly oxidized. Without the gearbox or hopup unit, I put the replica together for a test fit. Adding the TM Aimpoint replica red dot on top.
http://i16.photobucket.com/albums/b46/s ... nalFit.jpg
I think it looks pretty sexy.
WIRING/MOSFET
While I was waiting the paint to dry I started on the gearbox. Again, I was thinking of a CQB build, while still being viable outdoors. I wanted to maximize the rate of fire as inexpensively as possible.
Seeing that the electrical was the biggest hindrance I sourced some 12ga automotive wire for free, which is totally overkill for this project and I would find out later was a bad idea. First, I had to file out the channels that held the original, tiny, TM wiring.
http://i16.photobucket.com/albums/b46/s ... AG0514.jpg
http://i16.photobucket.com/albums/b46/s ... AG0516.jpg
Turns out this was unnecessary as I could just run the wiring behind the channels.
Placing the gearbox shell and wiring into the grip proved difficult as the wiring is just slightly too fat. Ideally, I should redo this in teflon wire, 16ga would probably be fine for my power levels.
I also set about learning how to make my own mosfets and I bought enough components to make 3 units, for less than $20 total. They really aren't all that difficult if you have any experience with soldering electronics, but would take more technical explanation than I want to do here. There are lots of guides online if you want to make your own, again, AirsoftMechanics.com being an excellent source.
The mosfet assembly with Deans connector:
http://i16.photobucket.com/albums/b46/s ... AG0519.jpg
And a 20amp polyfuse:
http://i16.photobucket.com/albums/b46/s ... AG0520.jpg
And plugged into the body to take my best guess at wiring lengths:
http://i16.photobucket.com/albums/b46/s ... AG0518.jpg
And the finished wiring:
http://i16.photobucket.com/albums/b46/s ... AG0517.jpg
http://i16.photobucket.com/albums/b46/s ... AG0522.jpg
http://i16.photobucket.com/albums/b46/s ... AG0535.jpg
All of this was done to handle the output of the biggest battery I could fit. With a higher rate of fire I would need as large of capacity as possible. Measuring the interior dimensions of the Laylax extended hand guard, I ordered an 11.1v lipo battery with a 25-50c discharge and 2650mah capacity from Hobbyking.com. They have the dimensions and weight posted for each of their batteries so I knew it would fit beforehand.
Putting everything together I realized I had a problem. The battery easily fits in the hand guard but connecting the wiring and sliding the hand guard on to the body proved impossible, unless I connected it with the battery plug facing towards the back but that caused the wiring to fold in on itself and bend the weak polyfuse connection.
As I result, I've researched a more compact way of assembling the mosfet and will arrange the polyfuse so that it can be attached below it, forming one solid unit with the wiring facing towards the rear.
Another problem is that when the hop up and barrel are place in the gearbox, the wiring prevents it from seating properly. It works if I force it, but it's too crude for me to be satisfied with and threatens to bend the connections of the mosfet and polyfuse. Solutions to both problems to follow later.