Primed to Belt the Competition!
This article was originally published in RC Driver’s October 2016 issue.
Photos: Edwin Rodriguez
Back in the day (like, way back) Serpent was known pretty much just for their purpose designed, on road racing rigs. Their 1/8-scale nitro GT and Prototype rigs were the go-to model if you wanted to win on the asphalt. Over the most recent years, the company has shifted its efforts more into the off-road realm. Starting with mainly 1/8 buggies and truggies, the manu- facturer now houses a variety of 1/10-scale race machines. The ﬁrst release of the Serpent Spider 2WD RTR (done by yours truly) was the ﬁrst to appear, followed by the race-bred SRX-2 rear and mid motor designs.
Building off of the success of the SRX-2 MM, Easton and his peers developed the SRX-4 to be a dominant force in 4WD buggy. This new machine shares 50 percent of its parts with the SRX-2 MM and there are option parts galore to tune it to excel on any track. The SRX-4 comes with either a CF or alloy chassis, gear diffs are standard and a low proﬁ le servo must be used for steering duties. Additionally, it employs a unique slipper design that can be run one of three different ways, allowing the buggy to be a competent performer on a host of different track surfaces. Spend your winters on turf and summers on dirt? Fear not, Serpent has got your back. They serve up a full complement of options for any racer out there on the SRX-4 including, but not limited to ball diffs, alloy upgrades, clicker options and more.
AT A GLANCE
WHO MAKES IT: Serpent
WHO IT’S FOR: Racers
PART NUMBER: 500010
HOW MUCH: $434.99
BUILD TYPE: Kit
• Dual belt drive for the ultimate in balance
• Fully capable on dirt, clay or turf
• Gear inserts to alter outdrive height
• Carbon fiber chassis and towers
• Super high grip on turf
• No droop screws
• Special tools (included) needed for some parts
This latest release from Serpent has got to be their crown jewel. The SRX-4 is the pinnacle of modern design, with a well thought-out setup born from decades of race history, including multiple championships won. Designer Billy Easton sought to bring something different to the market, but wanted not only a “niche” buggy in a crowded, shaft driven world, but also one that could dominate right out of the box. Well, after nearly two years in development, the SRX-4 is here to pick the steam back up where the SRX-2 MM had left off and it’s all about fast laps and podium finishes.
TOOLS AND ACCESSORIES INCLUDED
• Like the other new releases of the large scale variety from Arrma, the Kraton 6S BLX comes with a handful of spares, a full tool set and a couple XT-90 battery con- nectors for the packs of your choice.
• Brushless motor and speed control; 2S saddle pack LiPo (or shorty pack with mods to battery tray); Low profile steering servo; Radio and receiver; Pinion gear; Tires; Building tools and adhesives; Paint for the Lexan body
• Tekin 13.5 Redline Gen3 Brushless Motor (TT2707) $95.99 Power, reliability and tune-ability; those are the key factors that set the Tekin electronics apart from all others. To get the most out of our “stock” setup on turf, we opted for the 13.5 selection from Tekin. This Gen3 offering utilizes a 12.5mm rotor with an alloy heatsink can and adjustable timing to suit any driver’s needs. Not only that, but the limited power served up by this 13.5 power plant will help us to adapt to the SRX-4 without destroying it under mod class conditions.
• Tekin RSX D2 ESC (TT1158) $219.99 Not only is the newest version of the RSX ESC the perfect match for a Tekin Redline motor, it is also the ultimate in tuning, adjust- ability and data logging. Using the HotWire from Tekin, you can unlock the full selection of tuning options within the RSX. This ESC
also features a detachable fan, metal heatsink on top and it puts out high voltage BEC power for the steering servo of your choice. Meant specifically for mod racing, the newest RSX is still fully capable of running both sen- sored and sensorless motors.
• ProTek RC 160T HV Metal Gear Servo (PTK-160T) $109.99 The SRX-4 requires the use of a low profile servo so that the bottom won’t interfere with the front belt shroud. For steering purposes, we opted for the ProTek 160T. It features a coreless motor, all metal gears and it can operate on anywhere from 4.8 to 7.4 volts, making it perfect for this competition build. With the BEC on our RSX cranked to maxi- mum, we will see a stout 270+ ounces of torque at a transit time of .06 seconds! At those speeds, we hope our reflexes can keep up with it!
ADDITIONAL ITEMS USED
• Futaba R614FF-E 4-Channel FASST Receiver 4PK/4PKS (FUTL7632) $99.99 Using the best electrical components for power, speed and steering, it’s only fitting to use the best receiver on the market. The new version of the 614FF from Futaba is meant for 1/12-1/10
racing and has no external at all, making for a mighty tidy setup. It also weighs in at a scant 7.6 grams, so you can place it virtually any- where without disturbing that perfect setup.
• Pro-Line Pin Point 2.2” Z3 Tires (8228-103, 8229-103) $15.96, $15.16 To keep the bite high on the turf tracks we built this SRX-4 for, we chose these new Pin Points from Pro-Line. They are a smaller stud for turf tires, but they offer superior grip … so much so that we were forced to shave the outer two rows of studs off to keep from traction rolling. They are offered up in the Z3 compound which is a medium carpet com- pound, so they should last a good while.
• TrakPower LiPo 2S 7.4V 5400mAh 60C Hard Case Saddle (TKPC0420) The SRX-4 is designed with a saddle pack LiPo in mind, though the battery tray can be modified to run a shorty 2S pack (though it may require a bit of modding, cutting the front belt shroud open). For this reason, we used our trusty ole’ TrakPower 5400mAh sad- dle pack for our review. With a 60C discharge rating, it has plenty of snot to get our 13.5 powered buggy up and moving with haste.
HOP-UPS WE RECOMMEND
• Serpent Front Sway Bar Set (500499) $15.75 The SRX-4 comes standard with a rear sway bar, but there are provisions on the front end for one as well. With this kit on the front, you can achieve the ultimate in stability with your buggy. Serpent also offers a few different thickness options for both the front and rear, so you can tweak your SRX-4 to fit your needs.
• Serpent Alloy Chassis SRX-4 500461) 85.99 If you got the CF version of the SRX-4, but you have transitioned over to dirt track racing from turf, you’re probably going to want this alloy chassis … especially if it’s not a hard-packed, well manicured sur- face. This beautifully crafted T6 7075 air- craft grade alloy masterpiece is 2.5mm thick and milled for weight reduction.
The belt drive system that the SRX-4 utilizes for its 4WD is an old standard adapted to a new world design. The idea is simple; it effectively slices a bunch of weight from the entire driveline in the form of shafts and diff pinions while also centering all of the weight and power distribution. The biggest plus to running a belt drive rather than a shaft driven buggy is the fact that there is no torque twist to the side generated by the motor itself or the rest of the system components. Designer Billy Easton is to credit with this setup as he wanted to create a buggy that was both innovative and that worked well in real world applications.
Two years in the making (or thereabouts), the SRX-4 bucks the industry trends with an excellently crafted carbon fiber main chassis. These days, everyone is going back to alloy and while that offers a great deal of weight needed to keep the buggy firmly planted, it also leaves little to the driver as far as choosing where that weight goes. With this CF chassis platform, you can pick and choose exactly where to place your lead or brass to achieve the best results for your driving style and track conditions. In addition to the main chassis, Serpent also employed carbon fiber for the construction of the shock towers and if you’re worried about they’re durability … don’t. They’re a healthy 4mm thick and our numerous high speed traction rolls on the turf can attest to their strength. If an alloy chassis is a make or break type deal for you, Serpent is now also offering the SRX-4 in an Aluminum variant.
Part of the allure of this new competition rig from Serpent is the innovative design of the SRX-4. Not only is it semi-unique in this modern day with the belt drive, but it also eliminates the need for a top deck or chassis stiffeners. Why? Because the front belt shroud doubles as a chassis support, keeping things rigid and predictable no matter how you toss the SRX-4 around. Speaking of belts, I bet some of you are wondering how they’ll hold up, right? Well, let’s just say, you’ve no need to worry. They are both Kevlar reinforced and if that’s not enough to sway you, Easton ran the same belts on his first SRX-4 for the first three months, throughout extensive practice sessions with no skipping or stretching. Nuff said …
The slipper design on the SRX-4 is unique to this buggy alone in that it combines the diffs, slipper and clicker for the ultimate in adaptability. You can run the stock “locked” setup for high bite turf setups (as we did), you can install the optional clicker to act a a one-way setup where front brake bias can be adjusted, or you can achieve the ultimate in dirt track racing power implementation with the thrust washer slipper setup, controlling exactly how much power you want transferred to the front wheels. This last setup works as a center diff loaded with light fluid would … except there is no fluid in the SRX-4 so you won’t see viscosity changes leading to subsequent handling changes throughout long mains and qualifiers.
ON THE TRACK
Right out of the box, the SRX-4 has insane amounts of steering on turf … almost too much, actually. We had to dial a great deal of the throw out in the radio and add some expo to calm it down on the high bite surface. Like everything else on the car though, the steering components can be tuned to an incredible degree. There are different inserts available for the C-hubs and various plates for Ackermann adjustment … all included with the base kit. The angled steering posts translate directly to a smooth linear feel in the steering and absolutely zero bump steer or camber slop. After the initial run, we also opted to dial in a good bit of toe-in on the front of our SRX-4 to calm the initial response when entering a corner. As we said earlier, there is almost too much steering on the turf. Adding a few spacers under each shock piston should help settle the buggy a bit in the hard corners, but that solution might not be for everyone.
Running the slipper in stock conﬁ guration (full locked 4WD), the power out of the hole is amazing. There is no center shaft with the belt setup so you won’t see any torque twisting at all and the belt is whisper quiet (with the smooth operation and narrow body, everyone will think you’re running a 2WD buggy!). The Tekin RSX puts down some smooth power and even without any timing or boost, our SRX-4 was a rocket off the start. Top speeds weren’t all that spectacular, but we were running a “stock” 13.5 setup. Running the largest pinion we could (27t), the temps got a bit steamy on both the motor and ESC. A quick pop of the fan on the RSX solved the ESC issue, but if we’re going to stick with the 13.5, a second fan, some venting in the body might be necessary. Anyone who has ever run a Tekin RS or RSX knows how awesome the breaks feel and this setup is no exception. The SRX-4 bit hard in the tighter corners, but never showed a ten- dency to nose in if we grabbed too much brake; perfect for aggressive racing conditions.
This was Billy Easton’s initial goal with the concept of the SRX-4 and well … let’s just say he did exactly what he set out to do. Over the decades of running RC cars in both race and bash conditions, we have never, ever seen a vehicle that is so respon- sive to driver input. Simply put, the buggy goes where you need it to and you won’t feel like it’s ﬁ ghting you to do it. The 12mm big bore shocks and adjustable rear diff height really carry the tuning options to a whole other level, but on our turf car, we didn’t nec- essarily feel like a bunch of changes needed to be made from the stock factory build specs. As mentioned earlier, a bit less ride height would alleviate our lead-ﬁngered traction rolls, but a simple rebuild of the shocks with less travel will achieve the same goal. Not only is the SRX-4 a mighty nimble and aggressive machine, it is also forgiving. Any time we got a little too squirrelly in the cor- ners and sweepers, simply letting off the power a bit saw the buggy instantly settle itself. Jumping, well, that was a no brainer. Even hitting the approach a bit off kilter had the SRX-4 ﬂ ying straight and level.
The design features of the SRX-4 not only lend themselves well to a great handling machine, but also a durable one. The composite front belt cover provides a rigid structure to keep the chassis from ﬂ exing and the beefy suspension components can take a lickin’ while putting down the super fast laps. The absolute only concern we had when building the buggy was a tight spot in the rear diff that we just couldn’t get to smooth out. This could be due to the aluminum coated diff gear for strength, but after a few runs, the drive- train was much smoother. The super thick shock towers look great and are sure to stay in one piece during the gnarliest of crashes.
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SPECS AND TUNING OPTIONS
Length: 14.5 in. (368mm)
Width: 9.5 in. (241mm)
Wheelbase: 11.15 in. (283mm)
Weight: 3.8 lbs.
BODY, WHEELS AND TIRES
Body: Clear narrow body
Wheels: White dish
Wheel adapter type: 12mm
Tires: Not included
Shock positions: (Front) 2 arm, 4 tower (Rear) 2 arm, 4 tower
Camber: Adjustable links
Roll: Multiple camber link mounting locations
Wheelbase: Rear hub spacers
Ride height: Pre-load collars on shocks
Misc: Rear sway bar
Type: Dual bellcrank
Toe: Adjustable links
Type: Plate with stiffeners
Material: Carbon fiber
Transmission: Center diff
Differential: Gear diff front and rear
Clutch Type: Slipper/Clicker
Bearings: Full set
Feature Breakdown: 8
Overall Value: 8
To quote the late, great Glenn Frey … “everbody’s talking bout the new kid in town.” Serpent has surely shaken things up with the innovative design of the SRX-4 and even though time will tell the true tale, I’m sure this buggy is going to make its mark in a big way this race season. Turf is the in thing to do these days and this machine is primed for victory right out of the box. Smooth belt drive, nice light weight, all the steering and traction you could ask for and so much more. Well done Serpent. Well done indeed