Tamiya XR311 Project



In hindsight, the FMC (Food Machinery Corporation, interestingly enough) XR311 seems like a very strange choice for an RC model.  In fact, unless you happen to be a Tamiya fan, you've probably never heard of it.  A Google search returns much more information about the model than the real thing.  That's because the XR311 was a prototype vehicle (hence the "X") slated to replace the venerable Jeep but never went into production.  By 1977, when Tamiya released this model, the project had already been scrapped.  But if we assume that the model was in development for a year or two before that, Tamiya was poised to have a working scale model of a brand new military vehicle.  Now, 40+ years later, everyone has forgotten about it.  The Desert Patrol Vehicle came a bit later to fill the off road speed role and became the 58046 Fast Attack Vehicle.  The real Jeep replacement ended up being the High Mobility Multipurpose Wheeled Vehicle and became the 58154 Hummer, so Tamiya got their Jeep replacements in the end.  The Jeep itself became the 58033 Wild Willy.

The real XR311 prototype vehicle was intended to replace the aging original Jeep and maintain the legendary off road ability but add the capability for much higher speed with the option to add a wide array of military weaponry.  FMC created an interesting design using mostly Chrysler components.  Like most large Chrylsers of the time, it used torsion bar suspension and the A727 Torqueflite automatic transmission.  It also used a Mopar 318cid V8, but unlike any Chrysler it put the engine in the back.  It had full time 4WD and 11 inches of ground clearance.  I've rebuilt a version of both that engine and transmission before so maybe I'd actually be able to work on a real XR311!

The 58004 FMC XR311 was released in 1977as the 4th Tamiya RC car ever and also represented a lot of firsts.  It was the first off road vehicle (not counting tanks), the first to have four wheel independent suspension, and the first to have torsion bars.  It may have been the first to use a servo saver, but I don't know enough about the first three to say for certain.  The suspension layout (double wishbone) and spring style (torsion bar) does a good job of representing the real thing, and of course the body is spot on.  The motor is in the back, just like the real thing.  The weak point in terms of realism is that it is not 4WD.  The chassis is a flat metal base plate with suspension modules attached.  The body locks in place from beneath with an interesting cam mechanism which means no body posts are spoiling the appearance.  This model was resurrected by Tamiya in 2000 with the same model number and released yet again in 2011 which is the version I have.  Very little changed in all that time.  Apart from the obvious removal of the mechanical speed controller and associated servo, the main difference is the much needed replacement of the fragile plastic torsion bars with metal bars.  As a builder, the other important change is from slotted screws to JIS.  Yes, models way back then actually used slotted screws.  Good riddance.  Although the other 3 original models have also been re-released a number of times, they have used newer chassis that bear little resemblance to the original.  Of all the modern re-releases, this one probably represents the oldest near original build.

Although a model of a serious off road vehicle, the model is not suited for heavy off road use.  The body is fairly fragile and the suspension will bottom out over large bumps.  The model is most at home on uneven pavement or gravel, and it really shines there.  The suspension stiffness and movement is very realistic.  The model comes with 3 sets of pinion/spur combinations to vary the top speed and torque.  The model is quite quick with the high speed gears.  It is slow enough to crawl with the low speed gears, but doesn't have the traction to make a real go of it.  It does have a solid real axle with no differential so that helps a bit with traction.


frame
Page 1: Building the Chassis


Page 2: Building the Body
frame
Page 3: Upgrades!

Page 4: Final Photos

Description
Manufacturer
Model #
XR311 Combat Support Vehicle (2012)
1/12 Scale Radio Control Model Car Kit
Tamiya
58004
Mabuchi RS-540SH-6527
27T 540 Brushed Motor
Tamiya
53689
15 Tooth 32p Steel Pinion
Robinson Racing
0150
TBLE-02s Sensored Brushless
Electronic Speed Control
Tamiya
45057
2 Channel 2.4 GHz DSMR Receiver
Spektrum
SR215
Standard Ball Bearing Steering Servo
Futaba
S3004
XR311 Front and Rear Metal Kit
RC Channel
TA65311
XR311 Front and Rear Shock Set
RC Channel OP85055
XR311 Aluminum Under Panel
RC Channel MA75311
TS-28 Olive Drab Paint
Tamiya
85028
TS-79 Semi-Gloss Clear Paint
Tamiya
85079
Rubber Sealed Ball Bearing Kit
Fast Eddy
TFE1826

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©2019 Eric Albrecht