Tamiya Mammoth Dump Truck Project

The Mammoth Dump Truck came out in 2000 and isn't really like anything else before or since.  It is based on the huge 4WD monster truck chassis from the 58232 Juggernaut, which is itself an evolution of the original 58065 Clod Buster chassis.  This model throws out the Juggernaut's four wheel steering and balloon tires and instead uses flat tread haul truck tires.  Haul trucks are massive, slow mining dump trucks, the largest of which are capable of carrying in the range of 400 tons of payload.  The Caterpillar 797 uses an actual mechanical drivetrain, but all of the others are electrically powered from a diesel generator.  It is not clear exactly which real world truck this model represents, but it is an electric model like most of the real trucks.  The proportions are fairly accurate, but a real haul truck would have dual wheels on the rear axles.  The model features an unusual combination of 4-link suspension with leaf springs.  This is nothing like the gas cylinders used on a real haul truck, but it does provide a very stiff suspension capable of supporting a considerable payload.  The model is officially rated to carry 4kg, probably based on a reasonable limit of the lift system for the dumping bed.  I have put much, much more in it.

The design of this model presented some challenges to Tamiya.  Prior to the 1990's, pretty much every model used a mechanical speed controller.  By about 1993, most models were designed to use Tamiya's C.P.R. (which probably stands for something) electronic speed controller.  This couldn't handle the power demands of this big truck though, which is why the Juggernaut still used an old mechanical speed controller.  The problem with MSC's is that they convert excess voltage to heat any time you are driving at less than full throttle.  A mining truck is hardly ever going to be at full throttle which means the poor resistor would probably burst into flames.  As a compromise, this model contains the "Mechatronic" speed controller, a bit of a hybrid which is unique to this model.  It still uses a servo for throttle like an old MSC, but that servo turns a crank on an electronic board holding a FET resulting in real proportional control without a resistor.  The system is crude my modern standards but actually works well enough that I decided not to replace it.  The next challenge was the need for an extra channel.  Most radios of the time were limited to 2 channels, but a 3rd channel is required to control the lifting bed.  This is easily solved with a 3 channel system today, but Tamiya worked around that by including a "Plus 1ch" control unit which allows the steering (channel 1) to control the lift under certain conditions.  Finally, although the Juggernaut was not exactly fast, it was geared too high for a haul truck.  To solve this, Tamiya engineers removed the twin motor mount and replaced it with a single motor and extra stage of gear reduction.  Taken together, these three innovations made for a very capable and unique truck.

With four wheel drive, open differentials, and limited articulation, this thing can handle mild off-roading (grass) but not much more.  While there is ample ground clearance between the axles, the front bumper and grille are very close to the ground so obstacles are a problem.  This thing is really just for driving around the mine site.  The lift system for the bed is quite powerful.  I stacked it to the brim with rocks from my garden.  The suspension was able to handle it and the bed dumped without complaint.  There are no foams in the tires, but the sidewalls appear stiff enough to support the weight even when loaded.

So who bought this thing?  Apparently no one.  The first problem is that the Juggernaut chassis had earned a bad reputation due to failing gears.  This was fixed with the Juggernaut 2 (on which the Mammoth is technically based), but the damage to the reputation was done.  Beyond that, this doesn't have the same kind of appeal as a monster truck or buggy.  It is big and slow and lumbering.  You can't race it or jump it or even off-road it.  You have to drive it like a dump truck.  For all of these reasons the Mammoth is hard to find and costs a fortune.  I searched for a long time to find this one, but I am just the kind of strange customer who actually appreciates it.  I left it stock except for the addition of a lighting kit and a modern radio.

Update:  This model was destroyed in the 2022 fire.  It has not been replaced.

Page 1: Building the Axles	Page 2:  Building the Chassis	Page 3:  Building the Body
Page 4: Upgrades!	Page 5: Final Photos