PHOTOS RICHARD ESCOBEDO
1/10-SCALE ELECTRIC 4WD MONSTER TRUCK | KIT
Solid-axle tech meets short-course styling as Tamiya unleashes its newest monster machine
Tamiya is the original King of the Monster Trucks, having earned the title in 1987 with the genre-launching Clod Buster. The truck was a runaway hit and set the template for solid-axle monster trucks, and Tamiya has been the leader in “true” monster trucks ever since. The latest iteration of Tamiya's solid-axle supremacy is the TXT-2 Agrios, a fresh version of the TXT-1 (Tamiya Xtreme Truck) with stylistic and technical tweaks. With its new bodywork, and a slimmer overall stance thanks to narrower tires, this model is equipped with the Tamiya monster formula plus a turn toward short course. While the completed truck may appear “monster truck lite,” the TXT-2 is as burly as anything that's worn the double-star logo before.
Length: 20.08 in. (510mm)
Width: 13.54 in. (344mm)
Wheelbase: 12.8 in. (325mm)
Height: 11.10 in. (282mm)
Item no.: 58549
Weight, as tested: 10 lb. 11 oz. (4,851g)
Chassis: Vertical plate, aluminum and plastic composite
Type: 4-link trailing axle
Shock positions, chassis (F/R): 1/1
Shock positions, axles (F/R): 1/1
Shocks: Plastic, oil-filled with bladder volume compensation
Type: Enclosed transmission
Slipper clutch: None
Differential: Bevel gear
Driveshafts: Steel universal joint
Bearings: Metal-shielded ball bearing
WHEELS & TIRES
Wheels: Simulated beadlock, one piece
Tires: Chevron tread
Transmitter, receiver, speed control, and steering servo: not included
Motor: Mabuchi 540 (2)
Dual 540 motors give the TXT-2 surprisingly solid squirt, and allow the big truck to touch 20mph. The motors spin a common spur gear with integrated input gear.
The original Clod Buster mounted a single motor on each axle to deliver dual-motor power, but the Tamiya monsters that followed have all held their twin motors be tween the chassis plates and coupled them to a reduction-gear transmis sion. Not all the gear action happens in the transmission though; the axles are each mini-gearboxes them selves, and are loaded with metal gears throughout, including the cast- metal housings for the bevel-gear diffs. Splined shafts join the diffs to stub axles fitted in steering assemblies at all four corners. Out of the box, the rear wheels are fixed, but additional parts are included to assemble the TXT-2 for 4-wheel steering. The axles are joined to the transmission by telescoping steel driveshafts. Each driveshaft is equipped with dual universal joints, and while the manual depicts bushings being installed for the rotating parts, Tamiya actually supplies a full set of ball bearings with the TXT-2 (so don't be surprised when you have a gang of bushings leftover after you build the truck).
Each of the TXT-2's axles is also a gear-box. The all-metal geartrain uses bevel gears to transfer spin to a gear differential. The front and rear axles are identical, allowing the TXT-2 to be set up for 4-wheel steering.
In close up, the beefiness of the driveshafts is easy to see. The traditional universal-joint design is solid steel and secured by 4mm setscrews to flats on the gearbox and axle input/output shafts.
A view of the TXT-2's underside reveals the center transmission and the driveshafts that reach out to the axles. Note the large “pumpkins” on the axles, hinting at the heavy-duty differentials within.
PLASTIC/ALUMINUM HYBRID CHASSIS
The TXT-2's tires are from Tamiya's TNX nitro monster truck, and are narrow by “true monster” RC standards. The negative-off set wheels also make the TXT-2 appear less monstrous than Tamiya's previous solid-axle monsters, but when rubber mounted with traditional monster rims, the TXT-2 will instantly adopt the classic wide-track monster stance and proportions.
Monster truck fans panicked when the first photos of the TXT-2 appeared, as the truck seemed to be completely plastic in construction—hardly a sin for an RC model, but after the mucho-metal designs of the Juggernaut and TXT-1, a standard was set that black plastic just couldn't meet. Fear not; the TXT-2 chassis is actually built on aluminum rails and side plates. The rails are molded into a plastic framework, a construction technique unique to the TXT-2. While rigid on their own, the stout aluminum side plates that bolt to the frames make the completed chassis downright tank-worthy in strength.
Follow the TXT-2 Agrios build step-by-step on RCCarAction.com
Thick aluminum side plates and plastic/aluminum hybrid side frames sandwich the center gearbox. There's no shortage of beef here.
LIPOS AND LOW VOLTAGE DETECTION I completed the TXT-2 with a ProTek R/C LiPo pack and Tamiya TEU-106BK speed control. This speed control includes low-voltage detection, which is a must for any model with LiPo power. LiPo batteries will be permanently damaged if discharged below 3.2 volts per cell, and as its name implies, Low Volt-age Detection monitors the batteries voltage and alerts you when the battery nears the critical voltage. If you go LiPo, make sure your model is equipped with a speed control that features Low Voltage Detection, and make sure you activate the system if the speed control does not auto-detect LiPo batteries.
4-LINK, 8-SHOCK SUSPENSION
Each axle is supported by four oil-filled shocks, two per corner. The suspension links look like plastic, but rest assured, they're not. Note the steering servo mounted behind the front bumper/skidplate.
Along with its solid axles, it is the TXT-2's 4-link suspension design that makes it a “true” monster truck (as opposed to monsters with independent suspensions and A- or H-arm designs). The truck's suspension links are robust, thick-walled aluminum tubes anodized in a rich black (which contributed to the plastic-panic mentioned previously). Rest assured, these links are overbuilt if anything. The lower links follow parallel paths from the chassis to the axles, but the upper links are triangulated as they converge on the tops of the axles. This geometry allows the axle to stay centered relative to the chassis without the need for leaf springs (as used by Tamiya's earlier Juggernaut) or a panhard bar as some full-size solid-axle designs feature. Eight oil-filled shocks do the actual sus pending, and their Tamiya's time-tested plastic-body jobs. The shocks feature dual O-ring seals, bladder volume compensation, and plated shafts. Thread-on lower caps allow easy seal access, and while frill-free, the shocks are reliable performers proven in years of service on countless T-cars and trucks.
BEHIND THE WHEEL
As I bolted the TXT-2's included 540 motors into place, I mentally fast-forwarded to this moment where I thought for sure I'd be saying the truck could use more motor. Or motors, as the case may be. But it actually moves out pretty well, easily spinning its chevron-tread tires on the way to a top speed of 22mph on the ProTek LiPo pack I chose for testing. More power is always better, but there's plenty of fun to be had with the supplied motors, especially when you're doing more monster-trucky things such as scaling curbs and navigating trails as opposed to running for speed. Under acceleration, the longitudinally mounted motors torque the chassis and cause it to lean, lifting the inside left tire if there's enough traction. It's not enough to disrupt the truck's composure though, and it only increases the impression of power. As for handling, the TXT-2 requires room to maneuver as its turning radius is not very tight. If you want turn-on-a-dime capability, an additional servo and the kit's included 4-wheel steering parts will greatly enhance the TXT-2's tight-turning ability. I suspect a stiffer servo-saver may also help turning precision, but that experimentation will have to come later.
Fun to build
“Real monster” technology
Short-course styling and narrow tires not for monster purists
In terms of suspension, the TXT-2 rides like a truck (surprise). If you're used to extreme compliance of a softly sprung off-road car or truck with independent suspension, you'll find the TXT-2 to offer a much stiffer ride. It's the nature of this type of beast, as a solid-axle truck has far more unsprung weight to control as it navigates rough terrain. Wide, soft tires do much to help smooth the ride of typical solid-axle monster machines, but the TXT-2's narrower rubber offers less bump absorption. Speeding through rough terrain requires careful course correction as the truck can be bounced off-line, and hard jump landings may result in a rebound—but unlike an independent suspension design, there's no way to slap the chassis on the ground. You might bottom-out the shocks, but you'll never bottom-out the truck. Axle articulation is unaffected though, and the TXT-2 easily flexes its suspension to navigate its way down steps, through rocks, over roots, etc. Despite its high center of gravity, the Agrios can sustain surprisingly aggressive angles of attack without losing its footing, and there's much fun to be had in lining up different approaches on obstacles and testing the trucks limits. Throughout testing, the TXT-2 received no care other than battery changes, with no glitches to report other than a loose driveshaft set-screw that left the truck without rear-wheel drive (my bad, should have used more of the kit-supplied thread-lock). With the screw tightened, the TXT-2 Agrios has been trouble free.
TEST GEAR (NOT INCLUDED)
Tamiya TEU-106BK speed control
Futaba 3PM-X 2.4GHz FASST transmitter
ProTek 330T Super-Torque digital metal-gear servo
ProTek R/C 7000mAh 7.4V LiPo battery
For fans of “true” monster trucks, only solid axles will do, and no one does them like Tamiya. While the TXT-2 definitely breaks from monster tradition in its wheel and tire choices with the Agrios styling, this machine is 100% monster and can be dressed as wide and tough as you like. It's not an inexpensive model, but monster fans know the value that's here, which includes the decompression time spent at the bench turning bags of parts and plastic trees into a fully functioning RC monster. I had a blast putting my TXT-2 together, and I'm looking forward to what comes next as I try out new body, wheel, and tire combos. For updates, keep an eye on my blog at RCCarAction.com!