Build Complete: Axial Wraith MT

[fyrstormer]

A couple years ago I bought a Wraith, and over the next several months I sunk a ton of money into it to make it a good semi-scale rock crawler. It looks like this:



It's one of my favorite RCs, and I suspect it will be one of the longest-lasting too, because it's so overbuilt.

In the process of building my Wraith, I scrounged around for upgrades, and I found a lot of options that looked interesting but didn't really fit the vision I had for it. Over time those options piled up in the back of my mind, and I decided to build a second Wraith that used as many of them as possible. This is the result:



This Wraith started life as an original-model RTR, with the green-and-black body panels, mainly because I didn't want to have to install the light buckets myself. (what can I say, after building almost 40 RCs, I'm starting to get lazy.) The body came off and was put in the spare-parts box for my first Wraith, and it was replaced with the Poison Spyder body, which was trimmed in the front to accommodate the headlights. The stock electronics were also removed; the servo was replaced with a Hitec HS-7955TG, the ESC was replaced with a SkyRC Toro SC120 brushless ESC, and the motor was replaced with a Dynamite DYNS1616 550-size brushless motor.



Making the 550-size motor fit was a challenge; I had to cut away a lot of plastic from the center skidplate to make room for it. It was worth it, though, because the 550-size motor doesn't get screaming-hot like the 540-size motor I originally tried. With a 3800KV motor, a 19/54 pinion/spur ratio, and a 14/36 diff ratio, this truck goes a LOT faster than my first Wraith, and the motor is under a lot more stress.



As mentioned, the diffs were upgraded to a higher ratio, since I needed to replace the stock pot-metal diff gears anyway for durability reasons. The diffs are also unlocked, unlike my first Wraith. Since Axial's solid-axle diffs can't hold oil to save their lives, they are instead packed with silicone grease that won't leak out, and HPI "diff tuning springs" from the RS4 are installed on the spider-gear shafts to add a tiny bit more limited-slip action. (to be honest, I'm not sure how much difference it makes with those huge tires, but it can't hurt.) I thought I would miss the lack of limited-slip action in the diffs, but given the way this thing drives, lots of diffing-out helps keep the truck from powering itself into corners and traction-rolling. Since this truck is running so much more power than my first Wraith, and occasionally lands jumps on-throttle, the stock diff retaining clamps were upgraded to Vanquish aluminum bits.



Other than that, the drivetrain is pretty standard; no 2-speed transmission like my first Wraith has, no dig kit (what would I need it for on a truck like this anyway?), just steel gears in the gearbox and MIP X-CVD center driveshafts. I didn't even upgrade the dogbones in the front axle, because the stock parts work fine with the shallow steering angles this truck is capable of.

The plastic suspension links were replaced with Axial aluminum links. I could've gone with titanium links, but I wanted to keep the unsprung weight down as much as possible, and these links won't be getting dragged over rocks very much, so durability is less of a concern. The shocks were rebuilt with STRC's wonderful aluminum shock bodies and caps -- I have them on many vehicles now and they've always been a huge improvement for smoothness -- and filled with 15-weight oil and fitted with the softest springs Axial offers. If that sounds odd, remember that most of the drivetrain is unsprung weight, so there's not much work for the shocks to do, unlike with an independent-suspension truck. About half of the shock-absorption is actually provided by the big squishy tires. To compensate for the super-soft springs, I installed swaybars front and rear, using the stiffest swaybars in the kit.



When I built my first Wraith, I found out about the option to mount the steering servo in the front of the chassis. It seemed like a cool idea, but various people told me it limited suspension travel and raised the center of gravity -- two things I didn't want in a rock crawler. But for a solid-axle monster truck, I was more concerned about lowering unsprung weight, so a chassis-mounted servo seemed more practical. I looked at the various kits available, and eventually concluded the RC4WD kit was the best because it has the servo mounts integrated with reinforced bumper supports and an aluminum top-brace for the axle that has an integrated panhard mount.

Since I anticipated the steering would be under a lot more stress with the higher speeds, larger tires, and wider offset, I decided to get Vanquish clamping steering knuckles and rear lockouts, and their "Racing Ackermann" steering tabs. (they are longer than the normal steering tabs, so the steering links have more leverage when pivoting the knuckles.) I also decided to not run a metal servo horn, because I wanted some kind of sacrificial link in case I clipped the side of a tree with one of the wheels or something. So I installed the plastic servo horn that came with the Hitec servo. On the very next drive, I did indeed clip the side of a tree with one of the wheels...and the impact wrenched the servo loose from its mounts and broke one of the ears off the servo case. I was astounded. I will never again doubt the strength of Hitec's plastic servo horns. After some more experimentation, I eventually settled on a Team Associated heavy-duty servo-saver, which is actually stiff enough unlike all the other servo-savers I tried.



Now about those tires. They are HPI tires from the Savage 25, vented, with stock foams installed, and mounted on Maxximizer 3.2" beadlock wheels. The reason I went with this combination is because 3.8" wheels wouldn't give a tall enough tire profile for adequate shock absorption, 2.8" wheels don't have a good selection of compatible tires this tall, and 2.2" wheels would only fit crawler tires which have the wrong aspect ratio for a monster truck. Plus, I already use these same tires on my T-Maxx, so I only need one set of spare tires for both trucks.



Getting the right wheel offset for this build turned out to be the single most challenging part. The Maxximizer wheels have a 3/4" offset, which wasn't quite enough to give me the look I wanted. In addition, they have 14mm hexes, since they're intended to be used on the T-Maxx, whereas the Wraith uses 12mm hexes. So some adaptors were needed. I found a kit made by RC4WD to allow HPI Savage or T-Maxx wheels to be used on the Tamiya Clodbuster, and that seemed like a perfect solution -- except they actually had *too much* offset, and threatened to break the axles. eBay is swamped with wheel-widener kits, but the hardware that holds them in-place tends to be lacking; whereas the RC4WD kit has barrel-nuts that pass through the wheel-wideners and screw onto the stock axles, the eBay wheel-wideners were often held in-place with a simple pin, and that just wouldn't hold up to monster-truck driving. After several weeks of searching, I found an acceptable solution consisting of two parts. The first part was a different RC4WD kit called the "Mini 12mm extender kit", which had the offset I needed, but no 14mm hexes. The second part was a set of 12mm-to-14mm slip-fit hex adaptors from a Korean company whose name I can't remember anymore. Those parts combined finally gave me the offset I needed, and the build was complete.



The way this thing drives is unlike any other truck I own. It's rambunctious, jiggling side-to-side bouncing over bumps instead of soaking them up, but remaining surprisingly level while in the air. It drives pretty much exactly like I would expect a real monster truck to drive.

[fyrstormer]

Fixed all image links in this thread.

[redneck crawler]

Nice write up! How are you liking the truck so far? everything holding up?anything you would/ have you changed?

I am converting my Wraith over to a monster truck also. The biggest difference is that i will be running frame rails and a lexan body.
Really looking forward to unlocking the diffs and seeing if i can keep it right side up for longer than a few minutes.

~Leaky

[fyrstormer]

It ran great without any further changes, but I ended up selling it after a few months because I didn't drive it very much. Fast solid-axle vehicles have always been more of a curiosity for me than anything else; once I knew how it drove, I mostly lost interest.