CONVERTING AN AIRSOFT HENG LONG PZKPFW IV
TO AN INFRARED BATTLE SYSTEM

Foreward: 10/13/09- Three months after starting this article (and 3 tanks later), I'm dragging my feet on readying it for the WWW. That's because I now consider the tank less finished than I did when I finished the article's text. After lavishing attention on the other tanks, this one has become a poor bastard child that sits there, neglected. It has served as an IR systems test subject, a paintball target and as a camera tank, but beyond that-- nada. It hasn't inspired me to install working hatches (which I already bought), do additional putty work or progress beyond the basic primer coat.

The reason should be obvious from the funky video: The tank sounds like shit (or an alien insect), doesn't fire reliably, and drives like a racing car. It was so pathetic that I didn't even bother doing a 2nd take to make it appear to work better than it actually does. I'm sorry but it's true (and it'll happen to you!)-- spending lots of money on the other tanks has turned me into a snob. As I see it, the only path to redemption for this poor bastard is to expose it to the transformative effect of money. At the moment, the main obstacle is that a high-quality replacement hull isn't available for the Heng Long Pzkpfw IV (as it is for the Tiger I and the Pzkpfw III), so there's not much point in stuffing it with expensive, good-sounding electronics. In the meantime, enjoy this article, Buckwheat!

(Just kidding...)


And So It Begins: 07/15/09- Since I was getting a Tamiya King Tiger, I decided to convert my Airsoft Heng Long Panzerkampfwagen IV to an infrared (IR) battle system. Ideally, this would let me do battle with my wife (yeah, right), but more likely, give me an expensive way to test the King Tiger's battle system. This would be a somewhat involved modification that would direct me explore more of the world of 1:16 radio controlled tanks, and experience first-hand some of the issues that folks in the forums discuss.

THE BATTLE SYSTEM

The conversion is a multi-part process: First, the heart of the conversion is the battle system itself. The battle system interfaces the IR detector and emitter with the electronics, and some provide many extra bells and whistles that modify how the tank operates. Heng Long makes one, but it isn't compatible with Tamiya's, which appears to be the gold standard. Aftermarket products with Tamiya compatibility are available (with additional capabilities), and at this writing, there are primarily two popular and well-established systems to choose from: The full-featured "El Mod" system and Darkith's economical "DBC/DBU" systems. I decided to install the Darkith's system, since it was considerably cheaper, more compact, and less complicated.

For convenience and time-savings, I bought a fully assembled kit from RCTankWars.com. (The solder-it-yourself kit is a great bargain, and from the looks of the board shouldn't present problems for folks who know what a cold solder joint is.) Installing the circuits was very easy, with only a couple of solder points that were shown in the instructions. Phil of RCTankWars.com was very helpful and sent instructions and pics in e-mails, without prompting.

Actually, I don't have that much to say about it since it was so easy, and so issue-free... almost boringly so! It works well and noticibly improves the functionality of the Heng Long tank, even if you don't do IR battling. It fixes two of the most annoying things about Heng Long tanks-- the super spin "feature" and the exaggerated & violent recoil when the cannon is fired. You can turn them off if you want to, or leave them on. I believe that the momentum programming improves the drivability of the tank as well.

I tested the IR battling with my two tanks in my living room with minimal attention to setup, and had no significant problems. Both tanks rejected off-angle shots well. The minor gripes were that the Heng Long tank seemed to reinitialize too quickly, and occasionally, the tank would emit a high-pitched squalk. The default cannon sound is also a little bit too long and rumbly for my tastes, but I understand that can be changed. Those are relatively minor things. I guess I could also point out that the 'shroom (or "apple") is kinda homemade looking... but then it is, and they probably don't have a production factory to stamp out thin circular plates! It's an ingenious device and the main thing is that it works well-- kudos to Darkith for his brilliance in designing it, and to Phil for assembling and selling it.

RECOIL AND FLASH

The second part of the conversion is more cosmetic in nature, meaning that it's not strictly necessary, unless you participate in club battles with rules. Some clubs require that the barrel have a flash installed in the muzzle brake so that it's clear to all when you've fired your main gun. This is something that Airsoft guns typically don't have because the flash bulb or LED blocks the barrel. Similarly, to date, Heng Long Airsoft guns don't come with a barrel recoil (not that it can't be done, since Creeping Death's upgraded Airsoft turret mod does it); instead, Heng Long's tanks do an exaggerated jerking of the tracks to simulate the recoil which seems to be universally reviled (with good reason). The flash feature is very cool when it synchronizes with the cannon firing sound and barrel recoil, and I've been very pleased with the way Tamiya's King Tiger's system works. As I learned, Tamiya only makes it look easy (again, I'm reminded of the Mac versus PC thing that I've mentioned elsewhere).

There are a few options for recoil units: Tamiya makes one, Heng Long has recently released one that folks seem to like, and the Asiatam recoil/elevation unit. Although I like the Tamiya unit in the King Tiger, I knew that the recoil unit was just one part of the equation, which required the electronics that synchonizes the sound and flash. I bought the Asiatam unit because it offered both recoil and elevation in one mechanism, taking up less space in the crowded Pzkpfw IV turret. Asiatam, a German company, has a good reputation for producing high-quality aftermarket parts.

ASIATAM RECOIL AND ELEVATION UNIT: Indeed, from a quick impression, the unit seemed to be well-designed. It's a fairly large and squat plastic unit with a bunch of wires coming off of it with a bag of extra parts to attach the barrel. The space savings comes from combining both functions in one unit that occupies the central and forward section of the turret. The rear section (that housed the Heng Long elevation mechanism) becomes space for filling with something else (like a flash unit). Once I played around with it, I figured out how it was supposed to work (more or less). The elevation unit is a simple worm-gear driven eccentric shaft that goes one direction to raise, then lower the barrel, endlessly, just like the original Heng Long elevation unit, but in a more compact footprint. Unfortunately, the range of elevation travel is awfully limited.

The recoil system is much more tricky, but I think I've figured out how it's supposed to work: The barrel carrier is "loaded" forward by a cam driven by the motor and stops when it hits a switch that kills the motor's power. When the gun is fired (by left upstick-- same as preloading/triggering the airsoft gun), the motor pushes it over a stop tab on the cam and the carrier is suddenly pulled to the back by the spring. When the carrier hits the back, it closes a normally-open contact, and the LED flash is turned on. Meanwhile, the motor-driven cam continues to turn, and starts the forward cycle, opening the LED power circuit, and stopping when it hits the switch.

The kit requires that you install a momentary contact switch in the transmitter's guts; this is installed at the top of the left joystick's travel. It's wired so that it closes the "K" switch when you're at the top of the joystick's travel, which triggers the cannon sound, tread recoil and IR emitter (if installed). Therefore, when you push the left joystick up, you're first triggering the recoil mechanism cycle (barrel back, LED flash and barrel forward) and then triggering the cannon sound, track recoil, and IR emitter. If you stop in the middle, the recoil will activate and the LED will flash, but you won't get the sound, track recoil and IR emitter fire. (I should mention that the DBC system can modify the way the K button operates, depending how you've configured the DBC-- you can eliminate the track recoil.)

Pretty slick, huh? Now on to the fun part: The Instructions. If you thought that the old-school fractured English "Hecho en China" instructions were bad, this upgraded-for-the-Internet-Age rendition is even worse. Much, much worse. It's screamingly funny how bad they are, and while you've got to respect the Asiatam folks' technical prowess, it had me wondering what those guys were smoking. I'm not talking about cultural or language issues here (although they do add to the humor)...

The "instructions" are supplied on a CD... okay, that's a little bit unnecessary and over-the-top, but okay. The disk doesn't autoplay, so I poke around and see files with a .vcd extension. On my computer, nothing is associated with .vcd, so I have to find, download and install a freebie .vcd player. Grrrrr. The player starts; it's a slideshow. It's a sequence of pictures with jazzy video transitions in between. One problem: the pictures are so low-resolution that it's nearly impossible to see what's going on, even when you pause and zoom in. Arrrrrgh... Don't cameras nowadays have resolution better than 500 kilopixel? Clear pictures might be kind of important when you're trying to figure out where a wire is supposed to be soldered, dya'think? Maybe it's just the player I downloaded, but if I paused and tried to manually flip through slides, the freakin' presentation would go to the end, and have to be started again. I don't know how many times I suffered through the first few slides. And those forkin' annoying transitions. And then there are the captions... and you thought Chinglish was difficult??? Yaugggggh!!! In retrospect, it's funny. But I don't know why they didn't just put (good quality) .jpgs on the disk, or better yet, include printed instructions. So much wasted time... Sorry. End-of-Rant.

To install the unit, I recommend testing the electrical stuff first. This will let you confirm that the unit works (it's fun to play), plan your wire runs and install connectors and jumpers in advance, without having to work around the extraneous stuff. If you've installed the barrel holder but not the barrel, you'll need to turn the unit on its side, otherwise the barrel holder will jam as it returns forward.

There are 3 basic groups of wires: the 2 LED wires (which are easy to identify and guess their use), the 2 short wires and the 4 long wires.

The two short wires are an optional connection to the switch that's mounted in the hatch (the one that originally turned off the Airsoft gun). Use this if you want to be able to disable the recoil (why would you?). Otherwise, solder them together, or remove one and solder the other to the solder pad. This has to be a closed connection for the recoil motor to operate. Use the switch for something more fun, like turning on/off the headlights and convoy light.

The 4 longer wires are the important ones. The green, red and yellow wires control the elevation and recoil (formerly Airsoft gun). They solder to the small 3-pad circuit board that the original airsoft gun and elevation unit were soldered to. The red wire connects to the center. If you put the green and yellow wires in the wrong place, the joystick controls will be reversed (up would control elevation, down would control recoil/fire)-- no big deal to swap the wires.

The big question is what to do with the long black wire. As far as I could tell, the instructions give you no clue at all, or worse, mislead you. The black wire needs to connect to a solid negative ground ("GND" on the pic), found on the RX-18 board. If you try to use a connection point on the 8-pin turret plug, the best you'll get is an anemic attempt from the recoil motor to return to battery -- it will recoil backwards, but the voltage won't be enough for the motor to push the carrier forward against the spring's tension. Once you've verified that everything is operating as it should, you can tackle the task of installing the mechanism in your gutted turret. The only "gotcha" I encountered was that the barrel holder was too long-- either that, or I didn't enlarge the hole in the mantlet support enough. I can't say for sure because my mantlet assembly is different because it arrived in several pieces and had to be rebuilt.

INSTALLING HENG LONG'S HIGH INTENSITY FLASH Asiatam's LED flash is okay, but Heng Long's high intensity flash unit is much better! Sure, it's brighter, but more importantly, unlike an LED that stays on as long as it's powered, a flash charges and discharges...with a quick flash. As usual, the Heng Long flash came without any instructions whatsoever. I knew from some reference diagrams posted at forums where the 5-pin connector was supposed to plug in on the RX-18 module. I plugged it in without trying to reference the pinout, fired the cannon, and nothing happened. Hmmmmm... two of the pins have a wired plug-- I wonder what they plug into? I could hear the distinctive whine of a flash unit charging, so I reasoned that the plug must go to some kind of external trigger. I shorted the two and the flash went off... but the tank also played the cannon sound and did a violent track recoil. The track recoil was supposed to have been bypassed by the DBC, so it was clear that this wasn't the way to do it. Reading the diagram's pin designations gave me a clue: The first 3 pins were devoted to the flash unit-- positive and negative power on either end to charge the unit, and the middle pin was labeled on the diagram as the trigger. Sure enough, if the unit is charged, shorting the middle pin against the + pin will give you a flash without the track recoil and sound.

The easiest way to wire the trigger is to remove the LED and other connections from Asiatam's recoil unit's momentary contact switch, and wire the flash trigger and the + voltage there. The only problem is that the flash would happen at the middle of the recoil cycle (the same way the unit's LED configuration works), when it should happen at the beginning. If you wanted to get the flash at the start of the cycle, I think you'd need to find a different kind of momentary contact switch and relocate it to trip at the beginning of the cycle.

In my opinion, that's really not necessary since that level of precision isn't inherent in the rest of the system. The spring-driven recoil snaps back pretty quickly, so there's not that much of a delay. A bigger problem is that the DBC cannon fire sound is noticibly late. This really needs to be triggered at the start of the cycle since there's a slight lag in the triggering of the audio; the triggering switch is installed at the top of the joystick's travel, but should be earlier. You can improve the timing by pressing the "K" switch manually, slightly before you do the upstick motion.

In all honesty, the entire system is kind of a kludge anyway: The Heng Long system wasn't originally designed for it, so the joystick motion and the triggering of the K switch are two separate actions that don't take place simultaneously; they're only vaguely synchronized. You have to operate the system correctly for it to look convincing. Added to that is the problem that the DBC will enforce a variable delay between firing the IR emitter (depending on the tank class), but the recoil and flash don't respect it. The problem stems from the fact that it's really two systems trying to get along with each other. Darkith's system is amazing for what it does, but it would be better if it totally replaced all vestiges of the Heng Long system. Bear in mind that I'm only talking about the Heng Long compatible version of the DBC system, and I don't have any experience with the native Heng Long IR battle system.

After going through all of this, I better understand why organized tank battling seems to favor Tamiya as a standard; it works more consistently for all combattants, straight out-of-the-box (uh... after assembly!). For casual battles amongst friends, the modded Heng Longs are a lot of fun (and devising an unfair technological advantage might actually be part of the fun).

 


 

FINISHING TOUCHES

Heng Long 1:16 RC Panzer Pzkw IV

The Verlinden guy gets a lot of sit-in jobs, not because of his looks or his clothes, but because of his unique sawed-off-at-the-waist physique. I'm pretty sure that this was not a requirement for the real-world tank crew.

Pre-ramble, Four Years After 05/27/13- A lot of change has occurred in the hobby since I wrote the first part of the article (and all my other RC tank articles). First off, we mourn the passing late last year of Phil Pflueger (a.k.a "Blitz" on the rc tank forums), proprietor of rctankwars.com and distributor of ElMod and Darkith products. He was a leading proponent of the hobby, tinkerer extraordinaire, and an enthusiastic, friendly, generous, and helpful guy. He is missed-- Rest in peace, Phil.

Also, other mainstays of the hobby have vanished, notably rccommand.com. Bill was a good guy, helpful and generous, but victim to circumstances which made his continuing in business untenable. This is a huge loss to the hobby, as they were a USA source for a wide range of useful imported parts that found homes in many modded RC tanks out there. Fortunately, others have stepped up to carry the torch, although few truly fill the footsteps with the selection of the right stuff that rccommand.com offered.

Change is inevitable, but can be fatiguing and aggravating. The Spectrum DX6 transmitter (that I own) and its receivers, the AR6000 and BR6000 are commercially obsolete/discontinued. They've been supplanted by the DSM2 and DSMX technologies, which are more responsive and have additional features. That's only mildly relevant to me and my investment in the 1st generation DSM hardware since driving an RC tank ain't like flying an RC helicopter. Tanks can tolerate glitches, a less responsive drive, and you're not going to be operating it at distances where you can't tell if it's crawling along. So the DX6 isn't functionally obsolete for RC tanks. The main relevance is in trying to find a discontinued receiver that works with your obsolete transmitter if you want to upgrade just one more tank (but I did). For this project, replacing the Heng Long radio and receiver would be a first step in a serious upgrade, in tandem with replacing the rest of the guts. Although the old Darkith board was an upgrade, the nasty Heng Long engine sounds make it hard to love, especially if you've got other tanks with Tamiya and ElMod guts.

The ElMod folks haven't been sleeping either. They've discontinued all the hardware that I'd installed in my Heng Long FrankenTiger, and have a whole new lineup of their latest and greatest. My main gripe is that they never patched the problems with the version I bought (poor elevation servo operation and anemic drive power), and there's no reasonable upgrade path. I'm not going to invest another huge wad 'o cash in their current latest and greatest, even if it does let me control two guns and 20 bazillion lights. It's too big of an investment to just toss out on an even bigger investment, hoping that it lives up to your original expectations. There are other options nowadays, and if they pan out, maybe I'll rework the FrankenTiger too. (Sure would miss the ElMod sounds though!)

I'm considering the relatively new Clark TK22 board for my Pzkpfw IV upgrade. It's an amazingly low-cost (<$100) replacement for the Heng Long electronics (with much better sounds), with many of the bells and whistles of the ElMod board, minus the programmable sounds and more powerful audio amplifier. Since it's so new, it's hard to get and there appear to be some growing pains in the form of product revisions. Although I'm wary of that and there are bound to be some issues, the videos I've seen look and sound very promising. I'm particularly interested in the idea of using a servo for the recoil operation since the concept seems so straight-forward, particularly if the travel directions can be programmed with two different speeds. I've come to believe that the spring-operated designs of traditional "realistic" recoil mechanisms are inherently unreliable; they usually rely on a consistent balance of spring tension for quick release and motor power for return to battery. Over time, stretched springs change, and the mechanism may become unreliable. Because of this, I've reverted my King Tiger's Impact recoil upgrade to its original, reliable gear-driven mechanism. It's not as realistic, but it works every time.

As a matter of fact, of the four RC tanks that I own, the only tanks that I'm still totally satisfied with are my two Tamiya tanks. Their features are somewhat middle-of-the-road, but the design is mature and sets a high standard: They don't make me feel like I have to correct a deficiency and they're rock-solid reliable. Admittedly, they're not as challenging for a tinkerer, but I find that as I age, I have less patience for stuff that I have to constantly take apart and tweak.

Now That I've Got That Off My Chest... I was so disappointed with my Heng Long conversion as an RC tank that it took years for me to realize the entertainment value it offered as a static model project. Fact is, Heng Long does a decent job on the cosmetics, on par with the quality of castings that Tamiya does-- in fact, I swear that they perfectly recast one of the tanker figures included in a Tamiya kit! That's setting the bar fairly low because it looks like Tamiya hasn't kept up with the times in the area of injection molding technology: Their King Tiger's solid hatch handles made me think I was back in the sixties. Nevertheless, I believe that you can make a Heng Long tank look every bit as good as a Tamiya, given the amount of time, effort, and money you're willing to spend. If it's going to spend 99.9% of its life on a shelf, why not?

As always, the hardest part is getting started, convincing myself that it's something that I want to do. It's best to start with something that you can't wuss out of: I started by drilling holes around the outline of the crew hatches to remove and replace them with some metal hatches I'd bought years ago. Lots of Dremel grinding to clean the openings and grind flush the hinges and lips. It wasn't hard and didn't take very long, but I didn't see the point in doing it for the front brake hatches and the rear engine compartment hatches. It would have been harder to make those hatches' installations flush with the deck and there wasn't anything to see or access beneath them. The only reason for doing it would have been that a separate part always looks more separate than one that's sculpted to look separate.

This was my first time to use turpenoid and oil paints-- I'm a bit behind the times, but I didn't have a set of oil paints before. Hot damn! I was pleasantly surprised to find how well they blended and thinned, how smooth they went on, and how quickly they dried. Maybe that's why modelers use it? You can get very subtle shading with them, with much better control than using thinned acrylics. Also, you can rework the shading and smooth edges by re-wetting with turpenoid. Most of that subtle shading was lost underneath the airbrushing, dust-toning, and (my shitty and overdone) streaking, but it was fun to do. I'm not quite ready to graduate to the upscale and spendy MIG pigments yet: Maybe next decade.

Since it's more of a static model now (with shitty RC functionalty), it made sense to put the antenna where it should be, at the side. It's not an RC-functional antenna, which is why the rear antenna mount stays where it is. This would have been a non-issue if I'd just bit the bullet and installed Tamiya guts with a Spektrum 2.4 GHz system...

A good part of the fun was "research": Looking at pictures of built models for ideas and dabbling in scholarly historical information so I'd know if what I wanted to do would be totally off-the-wall. The Panzer IV is a great platform for modding since it had a relatively long and interesting evolution. Although I was interested in the schurzen (side panel armor) of later models, I decided that I preferred the un-panelled profile and plainly visible details of the stock F2 model... and it was easiest to leave it that way, as Heng Long intended. I chose to stay with the Afrika Korps motif mainly because the plastic is colored that way (practical, for scrapes)

I'm not happy with the way the turret numbers turned out, and if I were to redo them, I'd do a single digit. For one thing, it was hard to decide whether to align them with the slope of the door, vision port, the roof line or the hull line. Also, I think Heng Long placed the vision port too far from the door-- most pictures show a much smaller space between them, and the numbers shouldn't fit between the two. Finally, I think the numbers would be better if painted on since conforming a decal over the port and its bolts would have been extremely difficult, even with decal solvent.

Heng Long 1:16 RC Panzer Pzkw IV

Heng Long 1:16 RC Panzer Pzkw IV

Heng Long 1:16 RC Panzer Pzkw IV

 

The Forces of Valor 1:16 static die-cast M4A3 Sherman is probably what spurred my interest in finishing the Panzer 4. I got it instead of an RC version of the Sherman because it looked cool, had interior detail, and I felt like I'd "been there, done that" with RC tanks (the prospect of doing all that work didn't much appeal to me). It was partially an admission that I spend more time looking at my RC tanks than I do running them, and I like stuff with detail that's hidden beneath hatches. It was also a learning experience to see/touch/feel an upscale commercially weathered tank. It's awfully pricey for what it is (but cheaper than a Tamiya Sherman), and came in an absurdly huge 4-color box that sets a new standard in overblown deluxe packaging: I thought they'd mistakenly shipped a full-sized microwave oven.

I think it's unfortunate that there are both 1:16th and 1:18th scale military products, since they're so close but yet not quite compatible. 21st Century Toys did a great job making a huge variety of affordable 1:18 scale WWII stuff that would go great with the 1:16 scale tanks... if only it didn't look slightly underscale. The offerings in 1:16 scale figures and static support pieces is underwhelming, so the 1:16 RC tank thing appears to be doomed to remain in a limited world of its own. (The fact that 21C and its 1:18th scale line went under isn't a good sign for either.)

Forces of Valor 1:16 Sherman tank

Forces of Valor 1:16 Sherman tank

Naturally, I wish I could collect (and afford) tanks in 1:6th scale. Dragon has released a 1:6th scale static Sherman and Panzer II in kit form for a relatively reasonable price, compared to what you could spend for other 1:6th scale armor. However, it's a hard sell for me because 21st Century Toys' Stuart was so frickin' cheap, and it showed how impractical a collection of 1:6th scale armor is unless you've got a hangar to display them in.

21st Century Toys 1:6 Stuart

 

PART 2 - INSTALLING THE CLARK TK-22 BOARD


 

RC TANK INDEX