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HOW TO - Build A Rock Racer

Spotlighting Axial RTR and Bolt on Upgrades.

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HOW TO - Build A Rock Racer
By Tony Arnold - StampedeProject.com

With Axial’s RTR introduction and an ad campaign indicating a do it all Basher, Racer, & Crawler, I wanted to give my new favorite RTR a workout.  Out of the box, the 27T motor reminded me how much fun the Axial RTR could be in stock form delivering a great compromise of bashing fun and entry level crawling.  With upgrades, the destiny of the kit could go number of ways.  The body looks scale, so I could just drop in a brushless system or faster motor for a high-speed short-course truck.  On the other side, I could bolt up a 55T motor, lock the front diff and tune it for slow go crawling… or I could do both and build a Rock Racer.

The concept of a rock racer comes from the real 1:1 world of timed “rock running/racing” where you not only have to complete technical crawler courses, but also complete timed laps with jumps and other track embedded obstacles – kind of a trail running meets rock crawling. Setting up a rock racer RC is more than just dropping in a brushless system into your stock Axial kit.  All the standard crawler CG lowering tweaks are required along with beefing up durability to survive extra power and impacts at higher speeds.  Our build used Axial aftermarket parts and powerful Tekin electrics and turned out fast, durable, and still able to crawl over just about anything. 

1. DIFF LOCKING
Although locking the front diff greatly reduces the turning radius, It is required for rock crawling.  Installation is as simple as disassembling the axles and swapping the front diff internals with the included Axial Dif Locker and reassembling.  For those that will want to do less crawling and more short course racing, I recommend leaving the front axle un-locked for better high speed performance. 

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2. UPGRADING LINKS
Don’t immediately toss out the flexible stock RTR plastic links. I can tell you from experience that these plastic links act like bumpers and significantly limit damage from six foot plus falls especially at faster speeds.  To much flex when crawling is a bad thing so only the lower rear links were upgraded with Axial’s new milled links.  This gives our rock racer compromise between durability, higher clearance and stiffens up the suspension for improved crawling performance.  The plastic steering links provide too much flex when getting bound up while crawling, so for better control and more assured turning, I upgraded the plastic steering links to aluminum with an Axial Rear Steer kit.

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3. IMPROVING SHOCKS
The #1 Axial durability upgrade are aluminum shock bodies for smoother performance and worry-free durability.  While I had the shocks apart, the included ½” up travel limiters and two extra shock O-rings are installed under each piston to drop the ride height and CG for improved performance all around.  To add extra shock durability, two more o-rings were installed to soften down travel. Typically, I would go with heavier oil for crawling to slow shock response, but that would negatively affect our higher speed performance.  A good compromise is sticking with the stock 30-weight oil that will provide a slower suspension for rock crawling, but allows enough shock speed to be useful at higher speed.  I added three big shock spacers to the left rear shock to limit torque roll under acceleration and during binding while crawling.

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4. ELECTRICS
At the heart of a Rock Racer is typically a faster brushless motor and ESC that provides both low speed torque and high RPM top speed.  When we say "fast" on a rock racer that usually still means under 30MPH. For my rock racer I wanted to lean more toward crawler versus race, so I used a brushless Tekin RS Sensored ESC and 21.5T motor. Slow go torque is there, but if I need extra bashing speed, a 3S LiPo pack could be used with a little motor timing advance.  Although not intended as a crawler system, the Tekin RS brushless system powered with a MaxAmps 2S LiPo pack worked perfectly as a medium speed Rock Racer with higher than stock speeds and loads more torque for crawling. Unlike regular rock crawling, rock racers higher speeds will pull current beyond what a small receiver or crawler pack can provide so a full sized pack is required. Our full sized MaxAmps 2S pack was mounted to the rear axle simply by bolting on Axial’s Low CG battery mount.  This provides a huge CG improvement over the high stock battery placement and provides a relatively neutral front to back weight bias which is actually preferred for Rock Racer builds.

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5. TIRES & WHEELS
The stock tires are just fine for a Rock Racer, however just like I did back in our Axial Crawler Tuning article (May 2008), I  removed about 1/2" from the width of the tire foams and then do a shallow twelve-point star cut on the foams with help the tires to compress and add traction. "Airing the wheels" by drilling two holes per wheel allows the tires to breath and compress easily.  Unlike a typical crawler, I did not add extra weight this time to the wheels as the chassis would have to deal with extra rotational weight at higher speeds.  While the wheels were apart, I swapped out the stock gray beadlock rings with new red rings to match the red milled rear links – not a performance gain, but they sure look cool.

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6. DRIVESHAFT STRENGTH
Axial's driveshaft rings GREATLY improve the overall strength of the stock driveshafts.  Slip this on and glue in place with CA glue and the common problem of stripped out driveshaft yokes will be greatly reduced.

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7. BODY
If you are going to go through the trouble of adding a bunch of cool upgrades you might as well customize the body.  I choose another scale looking Axial Baja Buzzard body.  In order to give the tires a little more room during crawling, I removed about 5/8“ around each wheel well.  My paint theme was simple and used the included Axial Logo masks on the hood and bed.  I masked out the hood, door panels, and bed. Then I prayed the hood, door panels and bed with a light coat of FastKolor Pearl yellow through window screen for a carbon fiber look, removed the masks, and then painted the body black and applied stickers.

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7. MISC TWEAKS
The stock RX was relocated and mounted with double-sided foam tape to the back of the servo.  That reposition required the antenna to be moved to the axle mount which allows the antenna to get safely tucked under the body and chassis during crawling.

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GO ROCK RACING
If you have enough people in your local rock crawling club, you might be able to convince your club to convert the outdoor dirt track to a Rock Racing course once a week with a couple removable rock piles or other obstacles placed on the course.  You may not have a Rock Racing track, but setting up a timed run course in your back yard with a mix of long fast runs and jumps around your landscaping with some technical crawling sections also works great.  If Rock Racing sounds about like someone bringing a stopwatch to you neighborhood RC bash, then you are very close to how much fun this new emerging area of rock crawling is.  From Bash, to Race to Crawl, the Axial kit is flexible enough to do it all with a few upgrades. Hit the rocks, hit the throttle and go Rock Racing.  I guarantee it will be more fun than you have had in a long time.

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SOURCES: Axial Racing - www.AxialRacing.com, Tekin Racing - www.TeamTekin.com, MaxAmps - www.MaxAmps.com