I just found this thread from a Google Image search. WOW, that's crazy that you're also doing the same thing I am! Holy crap! I seriously thought no one gave two hoots about Toys so far as to go to the same lengths I am currently. I guess I'm not the only insane one after all!

Small world I guess, it was bound to happen! I am a prop maker, professional CAD artist, and hobbyist/jack-of-all-trades. I'd show you my portfolio, but all I have are loose pictures of my work and a blank LinkedIn since I'm too much of a lazy so and so to make it look pretty!

I work primarily in SolidWorks, but dabble in ZBrush, Keyshot, Photoshop, Illustrator, and tons of other software to get jobs done.
I've been working on my own replica for the last ~8 years, but my project has finally taken off into high gear as of last July. Last year I had the amazing opportunity to become the owner of the one original props (I got a
really sweet deal). The price was way too good to pass up to get nearly every measurement I could ask for. I've RARELY had success talking with prop collectors. They're always, understandably, very private -- as if what they own is "The Big Secretâ„¢," so it's really a breath of fresh air to not have to deal with asking them questions and simply have the object right in front of me to reference whenever.
My prop is marked #34, #38, and #39 in several places, so I can only assume it was near the end of the production run of 37 they made for the film. I have an old magazine from '92 that says some cool details about the props, exactly how many they made, how they did the turret firing effects, and so on. I have it scanned in at 600dpi, if you ever want to read it. It's pretty neat and sheds some light on things, with some cool never-seen-before pictures of the tanks with their firing mechanisms. Mine [unfortunately] doesn't shoot flames, but I have big plans for the replica.
The prop I own is in decent condition but needs several repairs which should be little issue for me. I have over 150GB of pictures and video taking the prop apart over the course of a week+ and measuring each part with calipers and such. And when I say taken apart, I mean stripped
bare. I of course am cadding it, but I had already started cadding it years before I owned the tank, using the picture method just like you. I wasn't far off on that original iteration, that's for sure. I was only a quarter of an inch off in overall length and width, and as far as the RC vehicle underneath, I was only millimeters off on that! So once I got the prop, all I had to do was go back and nudge things around a bunch.
Now -- having modified the CAD to be PERFECTLY accurate -- I am about halfway done. At the moment I am splitting it up for printing (I own an Ender 3 Pro and a Form 2), but still have several bits yet to be drawn up. I have also done photogrammetry on the Skull, Helmet, and overall fiberglass Body so I can trace it with maximum accuracy in addition to the measurements. I will also be taking it to be paint matched someday. Yeah... I have loads and loads of info, probably too much for one person. I probably know just as much as the original artists that made these (and I feel their frustration in trying to recreate it

). They did some pretty crazy, interesting, and novel stuff on this thing as far as props go. Some things are incredible ideas, and others are "eh, that could be done better."
Prior to owning the original prop I already knew what the RC vehicle underneath is: the
Kyosho Heavy Metal Monster Tank. Good luck finding one, they're SUPER rare and very expensive. Because it's from the late 80's/early 90's, people are really out to grab them up. If you can find one (in what I presume is the UK) I tip my hat to you! Mostly people in Japan own them, they're weren't terribly popular here in the US. They were expensive even at the time they were released considering how large and high part count they are (1/12th scale, NOT 1/16th, and ~300 parts). You're looking at anywhere from $300 for a crusty used one to $2500 for an unopened & unbuilt one, but perhaps less if you were lucky enough to find one at a random garage sale. They're not indestructible though, so there's definitely things to look for when buying one second-hand. They only show up on Ebay a few times a year, IF that, and when they pop up they sell stupidly quick. A
Kyosho Blizzard DX will also work, although with modification almost no one can tell the difference; they're nearly identical and from the same molds. It may be possible to print one, I have it fully cadded of course, but there are some strength concerns regarding that. It's such a rare & unusual RC vehicle; it's kinda funny to me no one here knew what it was! But then again, I was also in that same situation years and years ago staring at endless Tamiya stuff and being like "WTF is it?!"
I have enough parts to build two replicas. I plan on selling one and keeping the other upon completion. I estimate maybe the end of the year I'll be fully done if I'm lucky. I have probably sunk a grand or more into research & making this thing alone... I honestly don't even want to think about what I've spent so far.
If you wanna add me on Facebook, Skype, Discord or something so we can chat easier by voice or video, and share screens, I'm down! Maybe we can work together? You're clearly all-in on your project and doing fantastic work so far, send me a PM! Once you're up to speed, perhaps we could delegate work and reach this goal together? I could seriously spend a whole day or more talking your ear off about this thing with you; there's tons of information to take in. I could even send you replica parts I have extras or excess of, given things go well! I have a SendCutSend order for some of the metal parts coming in a couple days, and custom PCBs I designed later this month!
Attached is an older render from October. Still looks similar at the moment since the exterior is done, mostly on internal stuff now but could definitely put your skills to good use! I'm not terribly good at complex curved surfaces, so I've definitely been putting off the Skull and Helmet. They're also subtly asymmetrical since they're hand-sculpted, and I'd like to preserve that, so that makes it even more difficult!
