RC cars are supposed to be fast. Even if you’re not racing, the whole idea is to be speedy, right? Whether you’re slinging dirt or tearing down the street, you should be doing it like you’re on fire. That opinion does not stem from some unquenchable need for speed (I like slow airplanes). The main factor is that I require a challenge in order to enjoy RC…and where’s the challenge in driving a slow car? This mentality is what kept me away from RC rock crawlers for so long, despite their huge popularity. These are cars that are slow, sometimes really slow, on purpose. Hmm, no thanks.
On the other hand, this column is all about exploring every aspect of RC. So I couldn’t very well ignore rock crawlers forever. With only marginal excitement, I obtained a rock crawler and endeavored to find out what all the fuss is about. I can tell you now that I’m really glad I took the plunge. Despite their pedestrian speeds, I found that these vehicles offer unique challenges of their own.
What is a Rock Crawler?
As the name implies, rock crawlers are designed to climb rocks and rough terrain that other RC cars can’t handle. Crawling has expanded over the years to include more than just negotiating rock piles. These days, the term “crawler” encompasses technical rock crawlers, rock racers, and trail rigs.
Technical rock crawling is all about getting your vehicle over impossible obstacles. This activity is filled with radical, purpose-built machines. Rock racing is actually a full-scale racing sport in addition to RC. There are different aspects of rock racing, but the gist is that it combines elements of offroad speed as well as ridiculous obstacles (and mud, and noise). Trail rigs can still climb like a mountain goat, but they aren’t competition machines. They’re more about cruising with friends. Many trail rig drivers like to deck out their rides with scale details and drive them in places that normal RC cars dare not go.
The Axial Wraith
The crawler that I tested is the Wraith Poison Spyder from Axial Racing. The Wraith is available in a few other styles, but the differences are cosmetic. Although Wraiths are classified as rock racers, they are also very popular as trail rigs. This truck can be had in kit form or ready-to-run. I opted for a prebuilt Wraith that also included a 2-channel 2.4GHz radio. The only items that it didn’t include were a battery, charger, and AA cells for the radio transmitter.
Looking over the Wraith, I marveled at how so many aspects of this design are the antithesis of what I normally expect in a high-performance RC car. First of all, the motor is brushed rather than brushless. Brushed motors are typically preferred for crawlers because they provide better control at the low RPMs where these vehicles thrive.
Independent suspension? No, the Wraith has solid axles front and rear. Limited slip differentials? Negative. Here we have “locked” differentials (i.e. no differentials). Again, these aspects are not concessions to appease cost or manufacturing limitations. They are the preferred design traits that shape a modern crawler.
The Wraith’s chassis emulates the welded tube frames of full-scale rock racers. It does so with molded plastic parts which seem quite strong. The main part of the Jeep Wrangler body is a painted Lexan piece, while the roof is fiberglass. The body includes interior details such as seats and a steering wheel, but no driver figure.
This is a full-time four-wheel-drive machine. Since there are no differentials, equal power is provided to every wheel at all times. The only sacrificial link in the driveline is an adjustable slipper clutch on the primary spur gear. This is located near the center of the chassis, right next to the chrome-plated motor.
Steering is accomplished via a metal-geared Tactic TSX45 servo that articulates the front wheels to and fro. The radio receiver is mounted in a waterproof box under the hood, while the Electronic Speed Control (ESC) rests in a clip-in mount.
Per my usual, I replaced the stock battery plugs with Deans Ultra Plugs. There were bullet connectors between the ESC and motor. I omitted these plugs completely by soldering the relevant wires together. I also removed the on/off switch and soldered its lead wires together. Now the Wraith is powered on when I plug in the battery.
The Wraith includes soft offroad tires that are glued to the wheels. Axial sells other tires as hop-up parts, but the stock units have served me well thus far. My only complaint is that they stink…literally. Even after several weeks of airing out and numerous treks through dirt and mud, their pungent rubber smell lingers.
The suspension is a 4-link design that provides a lot of travel. It is rather amazing to see what this truck can go over without bottoming out the suspension. Four oil-filled, coil-over shocks provide damping. The outside of the plastic shock bodies are threaded so that you can raise or lower the spring caps to set the ride height that you want. I left mine in the stock location.
Out of the box, I noticed that the steering servo contacted the chassis and the body when the front suspension was compressed. I eventually figured out that the servo arm was not fully seated on the servo output shaft. Since correcting that issue, the suspension has operated as it should.
You can use 6-cell NiMH/NiCad or 2-cell LiPo batteries in the Wraith. The battery tray at the rear of the vehicle is a little awkward to access, but it fits either battery type. I tested the Wraith with NiMH and LiPo batteries to see if there were any significant performance differences. Both are Duratrax Onyx units: a 3000mAh NiMH and a 5000mAh LiPo. The LiPo provides noticeably more run time and slightly better top-end speed. Speed isn’t much of an issue with crawlers and run time is still quite good with the NiMH. So, I think either option is fine.
Driving the Wraith – A Rookie’s Learning Curve
I took the Wraith to a local sports complex for its initial outing. Set back from the playing fields are large mounds of dirt, piles of hay, and a small mountain of broken concrete chunks. I figured that those three surfaces would give me a glimpse into the Wraith’s capabilities. They did.
I first placed the Wraith at the foot of a modest hill of loosely packed dirt. I gently applied throttle and became dumbfounded when the crawler got hopelessly bogged down after very little uphill progress. Repeated attempts produced similar results. I thought “Um, when do we get to the fun part?”
I moved over to an area of hard packed dirt with a rather steep slope. My first attempt here was much like I had experienced on the loose dirt. Then I backed up a few feet and hit the slope with some speed. This time, the Wraith made intermittent progress. The wheels would spin until a tire grabbed a random rock or weed that provided enough traction to inch forward. Before long, it crested the 10 feet high pinnacle…success! I practiced ascending the hill until I could do it repeatedly without flipping the crawler over or getting stuck midway.
That mound of dirt taught me my first important lesson in crawling. I had incorrectly assumed that crawling was a purely technical endeavor. Either your rig can climb this obstacle or it can’t. I soon learned that driving technique is an equally important factor. Sometimes the difference between clearing an obstacle or tumbling downhill end over end is merely a few degrees of steering input or a jab of throttle at just the right time. The more I began to recognize these driving nuances, the better my success rate became.
I carried the Wraith and my enlightenment over to the concrete pile. Although the overall techniques required to climb the jagged concrete were different from those of the dirt hill, the driving subtleties that produced success or failure were ever present. I found predictably similar trends when driving on the hay stacks. I had stayed away from crawlers for so long because I thought that there was no driving challenge involved. I was wrong, and I’m sorry.
Since that first outing, I have continued to explore the Wraith’s capabilities and expand my skills at the wheel. I am constantly amazed by how this vehicle will climb over some impossibly menacing and complex obstacles. At the same time, I am often surprised by the places where it gets stuck or rolls over. Clearly, I still have much to learn about this rock crawling business.
With challenges still left to conquer, I don’t see my interest in crawlers waning anytime soon. In fact, the Wrath has become my go-to vehicle for backyard bashing. Its low gear ratio, big tires, and tall ground clearance ensure that no part of the yard is off limits. I also appreciate the 20 minute run times that I get with the LiPo battery.
Many crawler enthusiasts like to customize their rigs with driver figures, lights, performance parts, etc. I’m considering some performance upgrades for the Wraith, but I’m not so eager to add scale details. I’ve actually omitted some of the stock details such as the interior features and roof. After removing them to photograph the bare chassis, I liked the improved access to the battery tray. Just don’t hold me to that prediction. If nothing else, my experience with the Wraith has reminded me that opinions can change.
Byline: Terry spent 15 years as an engineer at the Johnson Space Center. He is now a freelance writer living in Lubbock, Texas. Follow Terry on Twitter: @weirdflight