This is part 2 of the saga begun in 2009, documenting the transformation of a cheap Heng Long radio-controlled tank into a money-guzzling cheap Heng Long radio-controlled tank. Money rules, man.


Heng Long Panzer IV Clark TK-22

06/27/13- I'd been giving the Pzkpfw IV another chance to redeem itself, to see if I had been too harsh with my previous assessment of my work done in 2009. To be fair, since I jiggered the recoil and it began working more reliably, it really wasn't that bad. It drove and turned well enough (although it's a speedy little sucker), didn't throw tracks, and did all the other things that a radio-controlled tank was supposed to. As I've said before, I might have been okay with it if it hadn't had such an obnoxious running sound. I also didn't like the cheapo Heng Long transmitter and that it required a long external antenna on the tank. Or the spotty synchronization of sound, flash, and recoil. So there were a number of little annoyances that made me like it less than my other tanks.

Selecting New Guts: My known options for doing something about this were limited and expensive-- Tamiya, ElMod, DBC3/Benedini --especially for what I considered to be a cheapo tank, not worth sinking too much money into. That's when you start entertaining thoughts of either living with it, or going off the deep end and splurging unreasonably. Sometimes, polishing a turd can be fun and the results may surprise you.

Fortunately, within the year, a relatively new option became available and at an attractive price: Clark Model's TK-22 board. I learned about it from the tank forum, and it has generated a lot of favorable buzz. The video samples supported this, so I was eager to give it a try. The place to go for it is the North American distributor, Immortal Hobbies.

Since this is a small niche hobby, there isn't a huge demand for these things, and consequently, they're somewhat hard to find. Vendors likely won't have a huge supply in-stock and I suspect production and shipment batches are relatively small. I was lucky because I didn't have to wait too long for the next shipment... but when you're as impatient as I am, it's a bummer not to be able to order and receive near-immediate gratification (sound of the world's smallest violin...).

Somehow I survived the tortured wait of a little over a couple of weeks. Naturally, there's a lot of anticipation and uncertainty surrounding a purchase like this. Even though other people have had great success getting it to work, maybe they're just a lot smarter than me? Would it work with my equipment? Would I like how it works? Will I have to buy more stuff to make it work? Faced with these kinds of questions, I didn't want to rip out the guts of my works-okay Pzkpfw IV before knowing that the new guts would work and be an improvement.

The Receiver: I was particularly concerned that my Spektrum DSM receiver (an AR6000) might not work with the board. It hadn't worked with my old ElMod board, which required a BR6000, a receiver with all-channels failsafe designed for battlebots. (As I've mentioned elsewhere, these are all obsolete and discontinued products that were made to work with my likewise obsolete Spektrum DX6 DSM transmitter.) I actually did find and buy a used BR6000 receiver specifically for this, but it was broken. Bummer. So I had to use an AR6000 that I'd pulled from a helicopter... or bite the bullet and invest in new equipment.

My motorized tests of the AR6000 receiver were worrisome-- the tank lurched forward about two feet right after turning it on. I fiddled with switching stick/channel assignments on the transmitter and diddled with the transmitter settings. The recoil triggered major track movement. If the transmitter was turned off before the tank, the tank would go non-stop runaway at high speed (as if it were angry). Arghhhh. I thought it was the AR6000, and that it was incompatible with the board. Well, not really. It was me and I was an idiot: I'd pulled the receiver from a helicopter and hadn't bound it with the transmitter set up for the tank. Once I did that, everything worked perfectly. Doh!

Sound Test: Actually, the very first thing I'd tested was the sound to find out if it was an upgrade that was going to make me happy. At first, I was feeling some major disappointment with the output level... until I realized that the board's socket wasn't wired the same way as my test volume pot. The documentation diagram came to the rescue, and the board, despite its miniscule dimensions, puts out a huge sound when it's connected to a good speaker. Another concern laid to rest.

Heng Long Panzer IV Clark TK-22

So I was more than happy with the sounds and loudness, and it was a major improvement. The cannon and machine gun sounds were crisp and sharp, the turret rotation and gun elevation sounds were subtle and distinctive, and the startup sound was suitably complex, but not overly long. The lights switch sound was an overly loud click, but since it was so transient, it wasn't objectionable. The running sounds were much nicer than the Heng Long's-- somewhat muted and subtle with a slightly peculiar pitch shift, but more natural and unoffensive. I could definitely live with it. Passing the sound and receiver tests gave me the green light to proceed with removing the Heng Long and Darkith electronics, and cleaning up the tank's innards.

It was surprising how much the Clark board cleaned up the interior, and how much functionality is packed into the single board. Instead of 4 boards strung together with bulky wire bundles and wires spliced into the Heng Long circuit board, it now has only 1 board, plus the Spektrum receiver. The single board sounds and works better and has more built-in functions too. Sweet!

Ease of Installation: I was also surprised at how plug 'n play it was, thanks to the board's use of Heng Long-style sockets. Most of the stuff from the previous installation plugged right in: The speaker, the power switch/battery, the motors, the remote volume control, the Heng Long strobe flash unit, the 8-pin multi-function turret connector. The included IR LED and gun flash LED (which I didn't use) had unusually tiny 2-pin connectors, but as I said, they were included so I didn't have to scrounge. Each plug's function was tested to make sure that it worked, and it's a marvelous feeling when you plug something in for the first time and it actually does what it's supposed to do!

Heng Long Panzer IV Clark TK-22

It got a little messier after I added a servo-actuated (mapped to the flaps channel) 3-pole switch (1 normally open/1 normally closed) to toggle between the hull LED machine gun and the turret laser machine gun. As originally wired (above), both machine guns would fire when actuated by the transmitter.

The Turret: I knew that the AsiaTam recoil/elevation mechanism would need work. I'd tested the "Real Recoil" servo option and loved it, so the plan was to gut that part of the AsiaTam mechanism and figure out how to mount the servo. Even though the AsiaTam mechanism takes up a lot of room, I didn't want to replace it because the elevation section worked okay (and otherwise I'd have to find something to replace it with). A benefit of the Clark board was that the up and down elevation could now be independently controlled by the stick (unlike the Heng Long circuit which drove the motor in only one direction).

Heng Long Panzer IV Clark TK-22

The turret is packed full with recoil servo, elevation mechanism, IR emitter, Heng Long strobe flash unit, laser machine gun, and socket for IR battle system (a.k.a.,"apple"). The weird kinks in the servo linkage are leftover from experimenting to find what worked; the rod extends the arm's length to make the recoil travel distance match the throw of the servo.

Real Recoil Servo Installation: My solution to adding servo recoil was pretty simple, but figuring out how to do it wasn't so easy. At first, I stripped the AsiaTam's recoil mechanism completely, but couldn't figure out where to mount the servo and the actuator arm. Once I restored parts of the cam-driven track mechanism (without the cam), I was able to see how a servo mounted off to the side could push and pull the mechanism. It just needed an extra long control arm to match the range of barrel recoil to the servo throw. I cut a rectangular opening in the AsiaTam casing so the servo could sit lower, and not bind against the turret's bottom cover. It also forces it to stay aligned in place.

The operation of the recoil is a thing of beauty. Not only does it snap back and slowly return to battery, but the flash and sharp crack of the cannon sound synchronize perfectly. I'm extremely pleased with the way that it worked out.

The IR Battle System: Even though I don't do the IR battle thing, the board had sockets for it and all the parts were already mounted in the turret. All I needed to do was replace the plugs from the Darkith cable and IR LED. It was relatively easy since the Darkith circuitboard had socket pin labels, and the Clark documentation listed the pin functions. It was fun testing it out since the old DX6 transmitter doesn't assign its model presets to a specific receiver, so I could put 2 tanks facing each other, do left stick up and down and the tanks would fire at each other and register hits. Of course, the downside and the reason to invest in DSM2 or DSMX would be to prevent this sort of thing! For what it's worth, the Darkith "apple" works fine with the board; even if you don't do IR battles, the IR receiver can be used with the optional Sony remote to program the board for different behavoirs.

The Transmitter Controls All the initial tests were complicated by the learning curve of trying to figure out how the transmitter was supposed to work. The board came with zero instructions, but they're available on the web. (A kind soul at has graciously tweaked them and made them available as .pdfs. They're very good, and essential to determine what plugs in where since the board has so many sockets, with no indentifiable function labels. The diagrams also indicate pin functions and polarity-- very important if you need to adapt cables, or just want to be sure that you're not going to burn out something by using a plug wired with reverse polarity).

The stick operation diagrams on the other hand, were a total mystery to me. It took me a while to figure out how to start up the engine sound, fire the machine gun, do gun elevation because I was trying to follow the diagram. (Instead, think like a stick-shift automobile; go up or down and cut horizontally, and don't think Tamiya) It's a bit like the ElMod scheme for 4-channel control. Kinda weird, and will take some getting used to.

[08/11/13- The Spektrum DX6 radio system was replaced with the highly-programmable Turnigy X9, which let me map the Clark board's controls for a more familiar feel (left stick vertical to raise/lower barrel, lights and start engine sound mapped to toggle switches, etc.). If you're interested, read this article for setup instructions.]

Conclusions: The refurbish took place over 3 days during the work week at a very leisurely pace, cleaning up stuff, adding improvements, and trying to figure out how to tackle problems like the recoil. The actual board replacement in a stock Heng Long tank could probably be done in under an hour, and depending on which one, might involve a minimal amount of soldering. Naturally, if you're retrofitting a modded Heng Long or using parts from different manufacturers, the complexity and time required increases... but that's a given and part of the joy of modding.

As you can tell, I'm very impressed with the Clark TK-22 board: It works well and does a lot at a very good price. I'm tempted to say that it's the best replacement option out there, but would have to temper that by adding, "for its price". I wouldn't replace my Tamiya DMD electronics with one even though they cost more and do less-- I just prefer the Tamiya's sounds, which have more "personality". The Clark board's running sound is a huge improvement over the Heng Long's irritating "alien insect" sound, but it's a little too unobtrusive and bland for my tastes. (The popular ElMod Tiger sound set goes a bit too far in the other direction... but can be changed.)

I also prefer the way Tamiya's fewer features map to my 6-channel transmitter. The Clark board (like the ElMod boards) maps a lot of features into the transmitter's left stick control in 4-channel mode. Consequently, there's a lot of accidental triggering of the features, like turning on the lights when you're firing the machine gun, or firing the cannon when you're changing the barrel elevation. These might be less of a problem with a different transmitter or if you were very practiced at it. The Clark board's side-stick control of barrel elevation is weird, and not very intuitive.

The Tamiya boards lack some cool features that are built into the aftermarket boards, like warm shutoff and startup, light control (most models), and momentum modeling (most models). Outwardly, this may seem like an obvious deficiency. However, they're easily added (at additional cost) via the extra channels on a transitter/receiver and using external hardware like Pico switches and a Turnigy board for momentum. These are functions that don't necessarily need a synchronized sound generated by the board (like lights switching on/off-- IMO, who cares?). The additional independent controls (flaps & gear) on a 6-channel transmitter are a better solution than mapping them to the left stick.

Obviously, you can get the same independent control with a Clark board because in 4-channel mode, you have 2 extra unused channels on a 6-channel receiver. I consider that one of its theoretical plusses over the Tamiya. The warm startup/shutdown and light control are built into the board so you can use one channel for machine gun switching, and still have one channel free to do whatever you can dream of. With the Tamiya DMD, you can only have two of those extra features because there aren't enough channels for all three with a 6-channel transmitter. (With my Tamiyas, I put the lights on a manual switch.)

I qualify those pluses as "theoretical" to contrast them with "practical", and I'd characterize the issue as featuritis, common to many products today (like touch-screen technology in cars). It's understandable because we humans are suckers for features and shiny things, so it sells product. Personally, I wish the Clark board had fewer bells and whistles mapped to the left stick because it's annoying and distracting when stuff gets accidently triggered. When I fire the machine gun, over half the time I move the stick diagonally back to neutral (instead of going to center and up), which toggles the lights with the loud click (thankfully it doesn't play the Notre Dame fight song). I'm tempted to tap power from the smoker socket and run the lights from a manual or Pico switch, but that wouldn't fix that loud click. From reading the documentation, it doesn't look like you can turn this feature off. So in that respect, what may seem like a plus can actually be a liability.

It may seem that these extra features come at the cost of intuitive left stick control (like having the cannon elevation mapped to the vertical travel of the throttle). I don't know if that's the case though, since I don't have a clue about what it takes to get this stuff to work. As an end-user, I wish the left stick operated more like the Tamiya controls, with the cannon and machine gun fire triggered at the extended range of the channels, beyond +100% and -100% of the vertical travel. I think the lights/aux features should work the same way, on the horizontal stick channel. Of course, this is easy for me to say and I'm sure the designers have thought of this and have a good reason for their design decisions.

One last thought on this long, rambling think-aloud: Putting on/off switch feature activation as a mix of horizontal and vertical gimbal coordinates is quite different from mapping continuously variable controls to those axes. With continuously variable controls, the user has continuous feedback: Move the stick more to the diagonal and what you're controlling does more of what it's supposed to do, in real time. With a coordinate-triggered switch, you get no positional feedback until it suddenly switches on. Consequently, it requires much more precision to operate. It makes sense to have things like this triggered from a clearly-defined reference point, like the neutral point, or ends of the travel.

There are some cool things that the Tamiya DMDs can't do that the Clark can do, such as firing the cannon and machine gun and operating the turret when the engine sound is off. (It's not the same as putting the tank to sleep. I say "engine sound" instead of "engine" because the Clark board lets you drive the tank with the engine sound off, which is a little strange and unrealistic, but useful if you want to add an upscale sound board for the engine sounds.) The Clark board's momentum simulation is turned off by default and can be enabled by using the optional TV remote programmer. (Or you can do it through hardware with a Turnigy servo speed control, which lets you dial in the amount of momentum you want.)

The biggest plus is its programmability, especially if you're an IR battler. You can configure a huge number of operational and IR battle parameters through the IR battle receiver using a Sony TV remote. The IR battle system options are far more extensive than Tamiya's, including things like enabling machine gun damage (obviously, all tanks in the arena would need to be equipped with Clark boards and properly configured). The remote is sold separately for a very reasonable price. I didn't get one and I'm happy with the default settings, but someday I might, to satisfy my curiosity. (I believe the default setup for my generic "German Tank" board is as a heavy Tiger tank. A TK-22 board with Panzer 4 sounds is also available, but wasn't when I bought mine.)

A frequently-requested feature on the forums has been a programmable custom sound function, like on the ElMod. However, the designer has stated that he will not pursue this for technical reasons. (Currently, you can send your board in to have it programmed with different sounds.) Instead, he has hinted at development in other areas, like a separate wireless board mounted in the turret to operate turret funtions so that the tank could be operated by a two-person crew. Interesting ideas! It does let you know that Clark Models is a fast-moving target, with lots of innovative thinking. Hopefully, it will lead to better products for the hobby at more affordable prices (and not to more abandoned, obsolete and expensive equipment to be replaced!).

An astute observer might notice a peculiar error in the physics of the recoil: When the cannon fires, the treads jerk the tank forwards instead of backwards! Ideally, the time to notice this would have been before shooting video, not afterwards. Fortunately, it's an easy fix (for the tank, not the videos). The pins in the motors' plugs need to be reversed-- black swapped with red. You can do this at the motor by soldering, or by releasing the pins at the plugs and swapping them (the easier way). On the transmitter, the channel's direction should be reversed (in my Mode 2 transmitter, it's the right stick's ELEVATOR channel).

Clark's generic German TK-22 board is configured as a heavy tank (Tiger I) by default, so it takes 9 hits to knock it out. (You can't change this unless you have the Sony remote programmer.) Unlike the Tamiya tanks, the engine sound doesn't change to a loping sound as it takes damage, but the speed is reduced in 2 stages of damage accumulation (12.5% and 25%). Turret damage simulation is on by default, but I'm not sure what it does since I have a hard enough time getting the turret to do what I want it to do when it's undamaged!


11/09/13- The fact that the Clark board doesn't need to have the engine sounds playing while the motors are running may at first seem to be a weird WTF??? flaw, but it turns out to be a serendipitous feature that none of the other boards I've encountered have: It lets you run an external engine sounds board like the Benedini TBS-Mini.

It's hard to believe that it wasn't designed deliberately for that. It's not an advertised feature, but why would they build-in the option for a silent-running tank (for a video capture tank?). The board's creator has emphatically stated that he would not design a custom sounds feature into the board, so maybe it is part of a grand design? Either way, it's an essential feature if you want to fix the most-complained about aspect of the Clark TK-series boards: The running sounds, and the inability to change them. All the other sounds are excellent and the running sound is a huge improvement over the Heng Long board's running sound, but it pales in comparison to sounds produced by the ElMod and Tamiya boards.

It's a brilliant product strategy since it holds down costs, which gives it a competitive advantage in the marketplace and gives the hobbyist a low-cost path to a major upgrade of the native Heng Long board. For folks who want to splurge, it offers the option of third-party upgrades. Although that more than doubles the total cost, the result is a high-quality set of features that compares well to ElMod and Tamiya solutions. (That said, each system has its own strengths and weakenesses, so there is no "best" system.)

I'd added a Benedini board to my Clark-powered Jagdtiger and was blown away by the quality of the sounds, so it was only a matter of time before I got one for this tank. Most of the particulars are covered in my Jagdtiger/Benedini article, so I won't go into that here. However, I will say that the Clark control board, Benedini sound board, and Turnigy transmitter are a fantastic combination that's fun to tinker with and yields a tank that's fun to operate and sounds great. Although the Pzkpfw IV is a humble tank compared to the lumbering giants like the King Tiger, Jagdtiger, Elefant, and Tiger, its small size, light weight, and narrow tracks make it a nimble performer that offers a different driving experience than the others.

At the start of this article (four years ago), I was skeptical that anything could turn this tank into a first-class performer and that it was pointless to try since a quality aftermarket metal hull wasn't available. Today, that hull still isn't available but I no longer think that it needs it. I believe that the right innards were all it needed: That's the stuff you notice when you operate it.

Jeez, it's hard to drive the sucker when you're trying to keep it in frame! The Mini-TBS loaded with the stock Pzkpfw III soundset, configured for manual startup. The extra sounds triggered by Prop3 include a different engine rev sound, cannon fire, 3 machine guns, turret sounds, and a couple German tank communication sounds.