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Kyosho Rock Force Crawler - Got Torque?
by Tony Arnold - StampedeProject.com

The 2.2 rock crawling segment continues to explode and now Kyosho has joined in with the 2.2 class Kyosho Rock Force crawler chassis. The Rock Force is a new from the ground up bomb proof competition crawler chassis which features some of the most advanced machining, chassis, and transmission engineering designs available anywhere in RC... think of if as a new Inferno MP9 for Rock Crawling.

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TRANSMISSION
Starting with the drive system, Kyosho literally put a different spin on crawling with worm gear drive/transmission. Worm gears offer a lot of advantages, they are more compact, stronger, smoother, deliver more precise control/less slop, are quieter, deliver high speed durability, provide more drivetrain clearance, position lock (prevent freewheeling), and can deliver so much gear reduction that a gearbox is unneeded - pretty impressive. For rock crawling, it's the ultimate.  You could easily pull 1/10th scale tree stumps out with the torque from the Rock Force's 30:1 gear reduction just at the axle (143:1 total).  Kyosho assured long-term durability with all hardened steel worm gears and drivetrain components.  The worm gear drive nets the loneliest looking gearbox in RC with only a motor mount plate and a non-slippered spur gear that allows for plenty of gearing changes to suit the user - very simple.  Since there isn't a transmission hanging up high, the worm gear drivetrain lowers CG as well.  The benefits of worm gear drives also spill over into electronics requirements.  Because of the gear reduction, Kyosho was right in saying a standard stock 27T motor delivers more slow go that you can imagine.  Worm gears also position lock and don't freewheel, so wherever the motor leaves the axle, is where it's going to stay until more power is applied. Even with an inexpensive ESC without drag brakes, the crawler will stay put at the most severe inclines.

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DRIVE SHAFTS
Even the drive shafts on this kit are unique featuring a dual telescoping design that beefy, beefy, beefy. The shafts are made up of dual internally hexed steel female shafts married with a floating steel hex shaft all covered with a free floating aluminum cover.  The drive shafts marry up the axles via heavy steel output yokes that could easily handle 1/5th scale power output.

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STEERING & LOCKOUT
The 1/8th scale class steering knuckles, bearings, worm gear output yokes, dogbones, and axles are a great example of how serious Kyosho was about delivering ultimate durability.  Integrated axle/hub cases are Kyosho's proprietary super thick plastic which should take extreme levels of abuse without failure. Rear toe-in grub screw lockouts like all the other steering linkage are big 1/8" thick steel pieces

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SHOCKS
More beef with 1/8th scale oversized threaded shock bodies with thick shock rods and milled brass pistons.  The plastic rod ends and the shock bodies are so thick that durability should not be a concern.  The milled aluminum shock caps up durability and the shock spring adjustment rings feature internal o-rings to assure your shock spring tuning stays put.  With the big shocks' damping capabilities, Kyosho recommends a lighter weight oil like the 25Wt I used.

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CHASSIS & LINKS
The Rock Force's Twin Vertical Plate (TVP) chassis design is similar to most crawlers with two chassis plates, a real metal skid plate, and multi-link suspension.  Looking more at the chassis, what isn't typical are huge links, a stock 4-link rear suspension, and three link plus Panhard bar (track bar) front link setup... a what? Panhard bar multi-link suspensions are usually only featured in specialized custom 1:1 rock racers and offroad 4x4s.  Kyosho is introducing the Panhard bar to RC with the Rock Force. A Panhard bar link is a 4th cross link that prevents the axle in a three-link suspension from moving laterally during articulation and thus provides more control, less torque twist, and decreases CG (center of gravity) changes. Kyosho definitely had the competitive crawler competitor in mind as the chassis provides a ton of tuning options. No need to tear down your shocks each time to tune your ride height for a course.  The Rock Force features simple but stunningly effective ride height tuning via front and rear limiter straps (zip ties) that still allow for full articulation. The servo mount was mounted very low for lower CG, however I am a little concerned that with the output of today's servos that a two servo ear/screw mount isn't enough to hold under extreme conditions.

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BODY
If you follow the instructions, you can't help but wonder if there will be anything left of the body after trimming.  All painted and decal-ed up though, it looks simply awesome and is very true to scale to typical 1:1 Jimmy bodied racing crawlers.  My paint job was simple dual color theme thanks to included window paint masks and a number of decals to dress up the body... I of course added a few extra of my own.  The stock body will due for us mere mortals, unfortunately it is not USRCCA (governing body) competition legal, however Kyosho thought ahead and included aftermarket body mounts for an easy body swap.

WHEELS & TIRES
The stock 12mm hexed wheels would have been usable, however they didn't offer enough clearance to allow the massive anodized aluminum hex nuts to fully thread and without thread lock, they work loose easily - I am still looking for one that was lost. By contrast the included stock tires were some of the best and stickiest tires yet to ship with a crawler with excellent overall traction once properly supported with a set of Pro-Line memory foams.

ELECTRICS
Kyosho noted that no special crawler motor or ESC was required, so I choose an Orion 27t Stock Formula motor and powered it with my old school Tekin Rebel 2 ESC.  The battery tray will hold any standard stick pack, but I used one of A123's new slim molded ultra-light hard case packs to improve CG further.  A digital 333oz/in. Hitec 7955TG titanium geared servo kept the wheels turning via a HiTec 75Mhz RX and HiTec PCX FM Transmitter.

TESTING
I ran the Rock Force though my standard test "crawler course of pain" to see where it shined or lacked compared to other crawlers and builds.  One thing you will notice immediately is that the drivetrain has near zero slop, so little that the the only detectable slop is the hex-to-axle pin movement - amazing. When paired with super low gearing it allows total control while crawling even at "the grass grows faster" speeds. Set up in stock form, the chassis is one of the most neutral reacting crawler kits with zero torque twist I have driven. I could work lines I could never have attempted with previous stock kits and even a few custom builds.  The diesel tractor like torque output is just awesome and powers you up and over inclines. The worm gear braking was also outstanding and even with the 27T motor, it stuck like glue without rolling. To test the durability I did my worse and flat out tried to break stuff.  The best I was able to do was strip the stock servo saver - excellent overall durability.

Testing the Rock Force on even loose limestone, I was reminded how very far we have come in only a year with out-of-the-box performance.  The Rock Force's performance exceeded any stock kit I have tested.  Much of that performance credit going to the very low CG design of the Rock Force, factory ride height adjustment tuning, stickier tires, lack of chassis torque twist, and advantages of the worm gear drive. In the hands of a novice or pro, a bone stock Rock Force delivers comp level performance.

WHAT WE LIKED
Until crawling came along, I felt we were in a RC engineering rut ... oohh big deal "now .5oz lighter"... but the Kyosho Rock Force represents some real ground up, head scratching engineering. The kit uniquely delivers some outstanding engineering ideas like worm drive and Panbar linking that just plain work. The reality is that with a USRCCA legal body, the Rock Force is competition worthy right out of the box. There is no question Kyosho has delivered the best handling, competition worthy, and most durable stock crawler kit thus far. Actually, from a durability perspective, this 1/8th scale parted RC in a 1/10th scale frame may be THE most durable RC available... period.  Optional parts are coming including high speed worm gears and sping sets for additional tuning. Then there is of course the "Dig" system parts that will alow turns on a dime even with all locked differentials... but that is another article.

WHAT WE WOULD CHANGE
Unseating Tamiya's $400+ CR01 kit as the new highest price crawler kit yet, the Rock Force's $550 street price will undoubtedly create a stir considering it still needs electrics, tire foams, and shock oil. On a kit of this level and cost beadlocks wheels and a stock motor are expected.

CONCLUSION
Sure the kit isn't cheap, but Rock Force owners will get an exceptional quality 2.2 class crawler with VERY durable 1/8th scale parts with more metal parts/pieces than competing models. The kit will pay for itself by greatly reducing or even altogether preventing breakage.  Even a jaded self professed crawler nut like myself who has over ten entry to competition level crawlers was very impressed with Kyosho Rock Force in stock tune. For those new to crawling, the chassis delivers very predictable performance that put a precision pro-level crawler in your hand without worry about breakage.  For those serious about competing, the performance, chassis, adjust-ability, engineering, and most of all, the durability of the Rock Force will deliver huge benefits - after all, the most important part of winning is actually finishing. See you on the rocks...

ON THE OTHER HAND
As of our review of the Rock Force, there were several other manufacturer's releasing crawlers, all with different engineering ideas. The Rock Force's strengths are its neutral twist free chassis, low CG, and mostly metal 1/8th scale durability without a minute of tweaking or $1 of upgrading.

HIGHS - Rock solid drivetrain married with competition grade components and chassis. TORQUE!!!
LOWS - This level of kit needs beadlocks. Motor, shock oil, and tire foams not included.
FINAL CALL - The engineering and components are worth the price in upgrade parts savings & crawler capabilities.

EQUIPMENT USED
Motor - Orion 27t Stock Formula

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ESC - Tekin Rebel 2
Servo - Hitec digital 333oz/in. 7955TG Servo
TX - Hitec CRX Spectra 3-Channel Synthesized Transmitter
RX - Hitec Synth DX 3ch FM Synthesized Receiver
Battery - A123 Nanophosphate Lithium-ion 2200 6.6V hard case pack

SPECS

Vehicle: 10th Scale 2.2 Class Rock Crawler
Type: Electric
Street Price: $550
Class Rivals: Axial AX10, Tamiya CR-01, Venom Creeper, Losi Comp Crawler

Drivetrain: Worm Gear
Pinion/Spur: 18 tooth / 86 tooth
Final Gear Ratio: 143.33:1
Differentials: Locked Differentials
Bearings: Full Bearings

RESOURCES: Kyosho - www.KyoshoAmerica.com, Tekin - www.TeamTekin.com, Hitec - www.HitecRCD.com, Team Orion - www.TeamOrion.com, A123 - www.A123Racing.com