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Axial Crawler Tuning Part 1
Tony Arnold -StampedeProject.com

You begged and pleaded and finally got your hands on one of the red-hot AX10 Scorpion crawler kits.  You even managed to scrounge enough electrics to get it running, but now what?  In this AX10 crawler how-to series, I'll go over the some cheap and easy Phase 1 tweaks to put some sting in the Scorpion.  

 Although the Scorpion is really quite good trail tuned kit in stock state, it could be tuned much better rock crawling.  Tires and springs are to stiff, the chassis is too reactive and suffers a little torque roll under load. The CG is also pretty high with a top mounted battery and high ride height.  Depending on the electrics you found, you may need to consider other options for crawling. Sure, I could start bolting on competition level accessories and do aggressive changes, but first let's see how good the Scorpion could be with a few tweaks and the right electrics.

1 Crawler Electrics
A motor that is too fast, a low powered ESC, or a weak servo won't let your crawler perform it's best. Without going overboard, we selected some popular and affordable crawler electrics for our first tuning session. For my crawling style and courses I like really high turn motors like the Axiom 75T to assure plenty torque. The Tekin Rebel 2 ESC has a full 6V/3Amp BEC output that sends plenty of power to our metal gear JR high-torque servo.  Since we don't need a huge Mh pack, a new A123 6.6v receiver pack was used to save space & weight and still provided almost an hour of runtime. The Spectrum system isn't entry level, but I simply don't want to use anything else now.

 2 Tire Tuning
The stock tires and foam combo is harder than what is used for crawling, however they'll perform worlds better with some simple tweaks.  Removing about 1/2" from the width of the tire foams and then doing a 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.  Cleaning the tires with Simple Green, drying, and then spraying on a liberal coating of WD-40 will soften up the tire compound, however you will need to periodically repeat the process to keep them soft.  I used stick on weights inside each wheel to add 5oz per front tire and 3 oz per rear tire for lower CG and added traction.

 3 Lowering CG 
Lowering the overall ride height and CG is the critical in improving overall crawling ability for any crawler -the target is usually just under 3" of center plate clearance for the 2.2 class.  It's an easy fix to drop ride height by 1/2" just by relocating the external stock up-travel limiters to inside the shocks under the pistons.  Since I am relocating the ESC and receiver, we can also ditch the top metal battery tray for extra weight and CG reduction.  I used spare shock limiters as spacers to take up the space where the tray mounts resided.  The battery tray braces were remounted at the front upper link location as the new low CG battery perch.  I used one of the anodized spacers that was left over from that modification to extend the rear upper link and moved the upper links in one mounting hole.  This slightly increases the angle of the rear driveshaft for extra clearance but more importantly changes the geometry slightly to lessen torque roll under a load.  Using my trusty Industrial Velcro I settled on attaching the ESC and receiver as shown.

 4 Spring Tuning
The stiff rear springs are about right however, a big fat pre-load spacer is required on the left shock to further reduce torque roll.  The front springs are a little too stiff to allow full articulation but moving the shocks to the innermost upper mount position helped. The light 30WT shock oil makes the chassis a little too reactive during crawling, but a simple swap to 70WT shock oil calmed down chassis movements.

 5 Body Swap
I love the stock body, but a smaller and thinner overall body helps to prevent snagging on the rocks and drops some top weight.  Seeing one too many "Bug" bodies on a crawler, I found a stylish 1/10^th scale '37 coupe body that, once mounted on trimmed body posts, was both compact and very narrow for optimal clearance. I managed to produce the paint job using two rattle can colors and an ArtTool The Return of Skulmaster stencil pack -no fancy airbrush work here.

 Testing
I did before and after testing with the same motor, ESC, and servo installed -the results were amazing. The stock setup strained to complete my typical "Crawler Course-O-Pain" I have set up in my rock laden landscaping.   The tweaked chassis however gave me a peak at its potential and struggled only on the more challenging sections.  Overall ride height was lowered by just 1/2", however the significant CG, chassis tuning and tire tweaks transformed the performance in a very dramatic way.  The body aside from looking really cool, provided loads more clearance, snag free crawling, and the shape helped with self-righting during tipovers.

 Conclusion
Axial has done a spectacular job on the engineering of the affordable crawler specific AX10 Scorpion chassis. It is great base for both "trail crawler" and "competition crawler" builds and allows plenty of tuning room for either. The simple tweaks made traversing near vertical obstacles a possibility and even greatly improved off camber crawling performance. Is there still room for improvement? Absolutely, but this is of course just the beginning of our upgrades. Next time we'll take the Scorpion to the max with some typical bolt on competition level accessories that will transform the Scorpion into one nasty little arthropod.  See you on the rocks.

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Sources: Axial -www.AxialRacing.com, Tekin -www.TeamTekin.com, A123 Racing -www.A123Racing.com, Axiom Motors -www.AxiomMotors.com, JR Servo -www.JRradios.com, BoLink -www.BoLink.com, Great Planes -www.GreatPlanes.com, Spectrum -www.SpectrumRC.com, ArtTool -www.Medea-Artool.com, WD-40 -www.WD40.com

http://www.youtube.com/watch?v=5K3sx6J1Kq8