Rock Crawling 102 The Next Generation Begins

Rock Crawling 102
The Next Generation Begins
By Tony Arnold – StampedeProject.com
RC Car - January 2008

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How to Tune Your Crawler
By Tony Arnold – StampedeProject.com

Yes even magazine folk who live and breathe RC humble ourselves regularly by what we learn over time. Recently I was diggin through article archives and stumbled on my very first RC Car Crawling Article “Rock Crawling 101” dating back to 2007. Great info back then based on the trends, but it definitely needed a revision after all I have learned so here goes the redue.

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The Rules
Crawling is regulated by USRCCA rules (US Rock Crawlers Competition Association) which defines two classes, “2.2” and “Super Crawler”. Since 2006, the 2.2 class popularity has exploded while the Super class has shrank. Although you can view complete vehicle and scoring rules at USRCCA.com, the basics are that points are assigned for DNF (Did Not Finish), DNS (Did Not Start), reversing, touching, repositioning, rollovers, repairs, and hitting gate markers (usually tennis ball halves) on the course – low score wins with timing also being a factor. Sounds simple, right? Not quite, finessing your crawler to a quick low score finish is extremely challenging, especially with some of the crazy courses that are being set up that can even include tightropes… then again sometimes it’s over thinking the simple stuff that gets you in trouble with points

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2.2 Class & Scaler Requirement Highlights
12.5” wheelbase X 12.5” total width max.
2.2” wheels and tires up to a maximum diameter of 6”
2-wheel front steering only
Realistic 1/10^th scale body
4-wheel drive
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Design Flavors
Back in ’07, the new Axial AX10 was just out with Wheely King, TLT, and Clodbuster based chassis dominating the crawler competition scene. In just over two short years, we have so much more to choose from; Axial, Kyosho, Losi, Duratrax, HPI, Venom, Berg, and others all offer great 2.2 class crawler chassis. We also have a few mini and realistic Scaler 2.2 Class chassis as well such as Axial SCX10 and Tamiya’s Crawlers.

Locked In and Going Slow
Back in ’07 55T-85T motors were popular. Then the search began to retain fine crawling precision with high RPM “leaping” capabilities. We all tried brushless with little success, then high voltage with high turn motors. Finally quality manufacturers caught up with more versatile offerings such as Tekin’s tough 3S rated FXR ESC and motor Crawler Combo available with motors from 35T-55T that filled the needs of crawlers.

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Tires, Wheels, and Foams…oh my
Ask any rock crawler guy what the most important component in crawling second to the motor, and they will usually say the tires. Just like a dirt track, with the right tire and foam setup you are 85% there from a tuning perspective. About a year ago I did a massive Pro-Line Crawler tire review with the help of some friends and we found there was no silver bullet. Sure there were favorites, but every driver has a different need. Before the Moab lead the pack, now several years later advances in tread designs, crawler focused compounds, and even the lowly foams have been upgraded to memory foams. Airsoft BB weighted tires have been replaced with stick on lead stripe weights and custom weighted beadlocks. The newest trend is beadlocks with integrated wheel weights such as Proline’s newest Titus Beadlocks or you could go with a super customized set of Mayhem Engineering Double Phatty Billet beadlocks

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High, Low, and Flexible
Assuring your chassis has no more than 60 total degrees of articulation is still a valid recommendation. Articulation allows one end of the vehicle to remain planted while the other end conforms to the impending object. Another set of chassis design goals which sound conflicting is to have very high clearance, but with a very low CG. Typically, the best option is to mount the RX, batteries, ESC, and servos just above the axels, however I have seen hundreds of creative ideas that provide lots of clearance with a low CG.

Other Crawler Stuff I Have Learned

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• Assure your upper arms are parallel with the ground.
• Assuming the chassis is relatively balanced without the wheels, the front wheels should be approximately twice the weight of the rear.
• Belly clearance should be 2.5”-3”. Most Pro Crawlers run around 2.75”
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• Crawlers that cannot ascend 69 degree inclines will not place well.
• More weight is not always better. Remember your electrics have to move all that mass around. I have seen prototype featherweight rigs that out perform heavy rigs.
• Invest in a obscenely high torque servo otherwise you will just burn out one servo after another.
• If you are winning or doing well, leave your rig alone & DO NOT CHANGE YOUR TUNING!!
• Get on RCCrawler.com and find a regional crawling group near you – there is a club near you

Tuning Tools
The old “board covered with sandpaper tuning trick”. Having a tuning board can be invaluable with initial tuning and chasing down tuning problems. Set board to a 65 degree incline and drive up it and back down. If your rig flips you belly height or weight distribution is off. If a right tire come up on it’s own then some preload is needed on a shock or more linkage tuning is needed. Keep it up until you can control a 69 degree ascent and decent. Using the board for off-camber transitions to a 45 degree side hill slope will also show if your tire foams are rolling to much and if stiffer foams are needed. Just so you have something to shoot for, a stock Axial RTR with a small battery pack relocated to the rear axle, zip-ties used to lower the suspension height and a strip of lead weight in each front wheel surprisingly will complete the above tests.

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Have Fun Going Slow
Where every RC hitting the market is getting faster and requiring either a $10,000 groomed track or a half-mile of abandoned road to realize it’s full potential, it’s refreshing to see a new category that allows fun in a small space. Crawling allows us to have hours of fun on the nearest rock pile or just climbing around the landscaping in the yard. You will never look at a pile of rocks the same way again. Now that we have demystified the basics of crawling and provided some ideas on how to build your own crawler, we hope you get you involved in this new “go slow” crawling segment.