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Build Complete: Traxxas TRX-4

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Build Complete: Traxxas TRX-4

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Old 09-02-2018, 11:20 AM
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Default Build Complete: Traxxas TRX-4

Traxxas was late to the scale-crawler game with the TRX-4, and even I already owned two other scale crawlers by the time the TRX-4 arrived. But when I saw what it was equipped with, I had to buy one anyway. A 2-speed transmission, portal axles, and remote-lockable diffs right out of the box?? Yes please! I don't even care if most of those features aren't actually useful for comp crawling, because I don't compete anyway, I just want those features because they're awesome. And I'm not the only one who thinks so, because I've read plenty of comments on many forums where owners say the TRX-4 is the best scale crawler they've ever driven -- once the "weight problem" is fixed.

Thus far in my ownership, the "weight problem" is the only problem I've actually encountered; the fully-accessorized Land Rover Defender body is tall and heavy, and the battery tray lifts the battery pretty high to clear the complex drivetrain (at least if you use a full-size battery -- there's a lower indentation to hold small batteries if you're cool with sacrificing runtime to get a lower CoG), so the truck is tippy in stock form. I wasn't willing to compromise on the detail accessories or the battery size, though, so most of my "work" for this build actually consisted of sitting around and waiting for manufacturers to make weighted parts for the drivetrain.

Anyway, here's what mine looks like:



I do love scale-accurate headlights on my scale crawlers. This truck has generic orange LEDs for the corner indicators, yellow LEDs from SuperBrightLEDs.com for the foglights (it's hard to find "yellow" LEDs that aren't actually some tint of orange instead), and Nichia DS Warm White LEDs for the headlights which look much more realistic than the cheap blue-white LEDs used in commercially-available lighting kits.



No, the asymmetric taillight setup isn't a wiring defect; that's how Euro-spec foglights work. Having one extra-bright light on the rear-left illuminates the corner of the car closest to you when you've just finished passing another slow car in the left lane, so you don't accidentally merge to the right and crash into it. Also, symmetry-breaking makes it look strange, so you notice it more easily when you can't see very well. So now you finally know what's going on when you see a VW, Audi, or Volvo driving down the road in perfectly-clear weather with the left taillight inexplicably brighter than the right taillight -- it's not because a lamp burned-out on the right side, it's because the driver of that car is driving with their foglights on for no good reason. Now you have one more reason to be angry at idiot drivers on the road. Sharing is fun!



You may have noticed the diamond-textured kickplates and mesh window grilles in previous photos; here's a closer look. I don't normally go for stuff like this, but when I was browsing Google Images for inspiration, I saw these parts and decided to give them a try. For direct-from-China eBay parts, they're actually quite good; they are actually made of steel, rather than cheap metal-finished plastic, so I don't have to worry about the surface treatment wearing off to show crappy translucent plastic underneath. They do nothing useful, of course, but they do help dress-up the rather large expanses of plain black plastic and plain black window decals that came with the body. You can also see where I removed the entire rear rack from the body; I may put something on there eventually, but the huge heavy spare tire was just too much dead weight in exactly the wrong place. It looked great, to be sure, but there's a difference between useless decorations vs. counterproductive decorations, and sadly the rear-mounted spare tire was in the latter category.

Okay, so I haven't actually discussed anything functional about this truck yet, and there's a reason for that; I haven't needed to do anything to make it run better.



As you can see in the picture above, the layout of the truck is essentially identical to the factory configuration. I replaced the Titan 21T 550 motor with a Holmes Hobbies TorqueMaster Pro 27t 540 motor, because that's the same motor I use in all of my other scale crawlers, and I replaced the plastic motor mount with a STRC aluminum mount (feel free to give Traxxas crap for using a plastic motor mount -- that's just a dumb idea), and there are extra wires running around for the motor endbell fan and the headlights, but that's basically it. The only drivetrain modification I made was to install the optional smaller spur gear and the largest pinion that would fit, so I could get 13mph in high gear on a 2S battery. Everything else works the way I want in stock configuration; how often have I ever been able to say that before??



So if all I did to the drivetrain was replace the motor and change the gearing, why am I now posting a picture of the front axle? Because there are a couple non-drivetrain upgrades I installed that are worth mentioning:

The STRC diff covers are clearly visible; I like having aluminum diff covers to act as bash-guards to protect the rest of the diff pumpkin from damage. The steering and suspension links are titanium, made by SSD, which frankly I only got because the stock steel ones were starting to rust. Traxxas deserves points for actually equipping a scale crawler with steel links out-of-the-box, and as far as I know, the other major brands *still* don't do this. If Traxxas had used stainless steel, there would be no reason to replace the stock links at all. But the most important upgrade is the understated black STRC portal-axle hubs -- those suckers are solid brass, several hundred grams of the stuff, as low on the chassis as is possible. STRC got my money because they were the first company to make a matching set of inner and outer, front and rear, which other brands inexplicably refused to do. I couldn't find brass inners for the rear axle from any other brand. That's fine though, I like STRC parts. So anyway, those huge chunks of brass, combined with the Pro-Line FaultLine 1.9" beadlock wheels that I use on all of my scale crawlers, do an excellent job of fixing the "weight" problem caused by the heavy accessorized body shell.

A couple final details I want to mention:



On my other scale crawlers, I used Losi Mini-T rear shock springs with washers soldered to the ends to make spring-loaded contacts for the body-mounted lights, but that wouldn't work on the TRX-4 because of the body-post design. My other scale crawlers have separate body posts, at least in the front, so a spring can be installed around each post for separate positive and negative electrical contacts. For the TRX-4, I ended up buying some battery-compartment electrical contacts on eBay, bolting the spring contacts to the front body-mount tower, and sticking the springless contacts to the underside of the body shell with foam tape, to make a set of spring-loaded contacts for this truck. The springless contacts are domed, which helps the spring contacts to self-center on the springless contacts when they touch; obviously they were never designed to work this way, because they're intended for use with batteries, but conveniently it works for my purpose anyway.



The front foglights on this truck are from the Axial universal headlight kit, but the rest of the lights are molded into the body and needed a different solution. Traxxas' lighting kit has arrays of surface-mount LEDs attached to circuit boards for the headlights, but I don't like that look; instead I shopped around on eBay for parabolic-style light buckets that would fit the TRX-4, and I found some 3D-printed light buckets from a company called "GRC". This is the first time I've used 3D-printed parts for anything, and I'm pleased with how they turned out. I painted the reflectors with Spaz Stix Ultimate Mirror Chrome airbrush paint (using a normal paintbrush, but it works fine anyway), so they would be more reflective, but other than that the 3D-printed light buckets worked perfectly out-of-the-box, no modifications needed. They are well-made and fit just right, which is always a gamble when buying aftermarket parts.



So that's my TRX-4. This is the last RC project I will have time to finish before my screaming pooping bundle of joy arrives, and it's anyone's guess when I'll have the time and money to work on any new RC projects. I'm glad I got this one done while I still could, because it looks good and drives well.
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Old 09-02-2018, 07:49 PM
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My foglights are always on. Don't hate.
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Old 09-02-2018, 09:25 PM
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Love these trucks (except the stock bodies, not a fan of those) - if I didn't already have a trail truck that I love (MST CMX) I'd buy one of these in a heartbeat.

Originally Posted by Dave_S View Post
My foglights are always on. Don't hate.
Front fog-lights, fine, because they give a wider spread of light at night.

There is no excuse for a rear fog-lamp being on unless absolutely necessary, as it is often as bright or brighter than brake lights. This makes your brake lights less noticeable (which is definitely a bad thing), as the following driver's eyes adjust for the brighter fog-lamp and the brightness of brake lights doesn't register as quickly.


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Old 09-03-2018, 06:25 AM
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Originally Posted by Dave_S View Post
My foglights are always on. Don't hate.
Stock foglights are pretty much useless for actual fog anyway. First of all they're plain white, which is terrible for fog because water vapor reflects the blue component of the light back into your eyes and dazzles your retinas; that's why proper foglights have strong yellow filters on them, because yellow light can pass through water vapor much more effectively. Carmakers used to use cadmium-crystal glass for foglight lenses, because it was exceptionally good at blocking blue light while allowing other wavelengths through, but they stopped doing that because cadmium is toxic.

Second, according to US Federal law it's illegal for foglights to be on without low-beams on as well, which totally defeats the backscatter-reducing benefit of using foglights at all. Although there really isn't anything stopping you from breaking that law, as long as you're willing to rewire the headlight relays in your car.

Third, when driving with foglights on in clear weather, all they really do is illuminate potholes that are already too close for you to avoid, because they are aimed to illuminate the space between your bumper and the near-cutoff of your headlights, because that's the only area you have any hope of seeing in dense fog anyway. If they are aimed to illuminate further out, then they aren't really foglights, they are auxiliary driving lights, which are actually illegal in most jurisdictions, to prevent people from bolting a dozen extra "trail lights" to their pickup truck and then using them on public roadways -- though again, you can pretty much do anything you want to your headlights and the cops won't care.

Hell, where I live there are tons of people who have those illegal HID retrofit kits on their cars, which spray light upwards into the faces of oncoming drivers, because the housings are designed to focus straight tungsten filaments rather than curved HID electrical arcs, and the cops never do anything about it. The cops also ignore the Jeep Wranglers with LED light bars turned-on on public roadways. Drives me nuts when I'm sitting in my second-floor study (or first-floor, for you Commonwealth types ) and I get blinded by cars entering my apartment complex with their illegal headlights on and aimed incorrectly. I suppose I should be glad they at least have their headlights on at all, given how many people around here will drive with their headlights off in the middle of the freaking night.

Anyway, the moral of the story is, Fyrstormer is very persnickety about proper vehicular illumination. Your right to see better at night ends when it blinds everyone else on the road and makes accidents more likely; if you really need that much extra illumination to drive safely at your chosen speed, then your chosen speed is too fast.

...what was this thread about, again? I've forgotten.
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Old 09-03-2018, 10:45 AM
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I used a jumper so I can use low beams and fog lights. I haven't driven my car that has fog lights in a couple years.

I was just joking with my comment though, nice traxxas.
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Old 09-03-2018, 12:15 PM
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Eh, misuse of foglights is just a pet-peeve for me, which is why I put attention into getting that particular detail correct on my Defender. Horrible glaring headlights are a much more serious problem; that one I do actually get angry about. I have very light-sensitive eyes and it's easy for me to get blinded by badly-modified headlights.
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Old 09-03-2018, 10:46 PM
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I forgot to say, pretty freaking clever powering the lights on the body like that. At first I didn't notice the springs had wires going to them.
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Old 09-04-2018, 07:11 AM
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Thanks! I was quite happy when I tried a similar setup on my first scale crawler and it actually worked.
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Old 11-07-2018, 01:28 PM
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Excellent interesting post. Thank you. Love the idea for the contacts. VERY VERY nice TRX4.
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Old 11-08-2018, 11:59 PM
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Thanks!

Oh, I forgot to post a minor update; I took the advice of someone on RCCrawler and got an aftermarket accessory mount for the tailgate from Shapeways, so I can have decorative bits on there without the glaring hole left by the missing spare tire:

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Old 11-13-2018, 09:44 AM
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looks great!!
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Old 06-24-2019, 06:47 PM
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What does the Holmes hobby 27t motor do for the truck that the Titan 21t didn't? How good is the drag brake on the stock ESC? How well does this truck crawl compared to a Wraith?
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Old 06-24-2019, 07:40 PM
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In attempt to help lower cog in mine I installed different battery tray.

I want to probably try and duplicate fyrstorfyr's method of powering lights
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Last edited by Dave_S; 06-24-2019 at 07:52 PM.
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Old 06-26-2019, 09:44 PM
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Originally Posted by MaX-D View Post
What does the Holmes hobby 27t motor do for the truck that the Titan 21t didn't? How good is the drag brake on the stock ESC? How well does this truck crawl compared to a Wraith?
Rebuildable motors have stronger magnets than disposable motors. That makes rebuildable motors more efficient at low speed, allows them to produce more torque, and increases the drag brake. Some of these things are not good for high speeds, but they're very good for crawling and trailing.

It's been long enough that I don't remember what the stock ESC was like anymore. But generally speaking I prefer an adjustable ESC anyway, because I can make it work the way I want.

The TRX-4 is a very different vehicle than a Wraith. It's hard to compare the two. It won't be able to climb a vertical rock face to get over an obstacle like a Wraith could, because its front tires don't stick out in front of the bumper like a Wraith's tires do. But the TRX-4 is more interesting to drive on moderate terrain compared to a Wraith. A Wraith will easily handle any obstacle small enough for it to climb over, which is better for carefree bashing, but less interesting if you want a technical driving experience.
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Old 06-26-2019, 09:54 PM
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Originally Posted by Dave_S View Post
In attempt to help lower cog in mine I installed different battery tray.

I want to probably try and duplicate fyrstorfyr's method of powering lights
Who makes that battery tray? Does it fit a full-size LiPo or only a shorty?

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