Cross RC Maz 537 Project

This thing cost a fortune....

My experience with Cross RC so far had been building the 6x6 UC6 truck which I really enjoyed.  Cross doesn't have much marketing presence in the USA so I kept my eye open for new releases on the Facebook group and got a chance to pre-order the new BC8 Mammoth before it was even released through the new Cross RC USA website in Wisconsin.  I waited impatiently for a couple of months until it finally arrived.

This is an 8x8 Maz 537 truck with all driven, locked axles and a 2-speed transmission.  Most big multi-axle trucks have solid axles.  The well known Tatra 815 has independent suspension with swing arms, but this goes one step further with double wishbones all around.  The front axles are sprung with torsion bars while the rear axles are connected together with a walking beam.  Both front axles are steered.  The included motor is a 560 size behemoth.  I bought the flagship version of the kit which swaps out the plastic suspension arms, hubs, and transmission housings for all milled aluminum.  The kit comes with a sound kit and working light system as well.  The "engine" can be remotely started, the horn honked, the headlights turned on and off, and the blinkers and brake lights are functional.  There is even an overhead light inside the cabin and the instrument cluster is illuminated.  The weight and solidity of this model can scarcely be believed.  While at 1/12 scale it could be considered smaller in scale than many kits, the absolute size is massive.  It weighs 20+ pounds. Virtually every part of the chassis is metal while the body is built like a scale plastic model kit.

You might expect a model of this size and weight to be sluggish, slow, and cumbersome but that's not so.  I run it on a 3S Li-Po and it is as fast as you could possibly want in high gear.  In low gear it will crawl over nearly anything.  The independent suspension soaks up bumps admirably.  Since the rear axles are unsprung, the 5th wheel can support a very heavy trailer tongue.  The winch box behind the cab initially contained only a fan for the motor, but I added the winch later when it became available.

It is pretty obvious that a truck like this is made specifically to pull a trailer, and the carefully designed fifth wheel on the model made it pretty clear that a trailer would be forthcoming.  The first trailer to be released was a nicely designed logging trailer that could be stowed on the rear of the truck with the help of the winch.  I had already built a different logging truck so I waited for the second trailer, a huge lowboy trailer with a gooseneck designed for hauling heavy military equipment.  The trailer alone costs more than most RC models so I was on the fence about it but I got a good deal from my local hobby shop.  The T247 is an absolutely huge model bringing the overall length of the assembly to about 7 feet.  I also weighs a ton with 8 metal beadlocks and cast metal walking beams.  The loading ramps are motorized and controlled from the truck.

It doesn't make much sense to have a huge, high capacity trailer with nothing on it, so my plan was to use a tank.  The problem is that most RC tanks are 1/16 scale which makes them look way too small on this 1/12 scale trailer.  The Internet came to the rescue in the form of Exclusive RC who designed a 3D printed Soviet T-72 tank in the correct scale.  It cost a lot too, but there was really no other option for a scale load.  Luckily, I was very pleased with the quality of the printing and detail of the model.  The tank is not functional but it is very heavy, sturdy, and accurate.  It looks perfect on the trailer.

Even with all the load of the massive truck, trailer, and tank, this think has no trouble driving off road and can even maintain speed in high gear.  I feel pretty confident in saying that I am unlikely to ever have a heavier RC rig (unless I get one of those 1/10 scale tanks).

This is the most complex wiring system I've had to do so far.  7 channels are required to control everything, but I only have 6 so I alternate between control of the winch and trailer ramps.  The following is a short explanation of the way I set up the model electronics.

• Channel 1:  Steering.  There are two steering servos wired in parallel and powered directly from an external 14A BEC set to 7.4V.  Luckily the kit includes a distribution block which connects the BEC to the dual steering outputs without running the high voltage to the other channels.  This allows everything else to run on the 6V from the ESC.  This channel needs to be routed through the light kit as well to control the turn signals.
• Channel 2:  Throttle.  The throttle channel needs to routed though both the light kit and the sound kit.  The light kit responds to the throttle signal with the brake lights and the sound kit adjusts the engine pitch as a function of throttle position.
• Channel 3:  Transmission.  A two-position switch allows selection of high or low gear.
• Channel 4:  Sound.  A three-position switch is used here.  One direction turns the engine sound on and off and the other direction sounds the horn.
• Channel 5:  Lights.  A momentary switch turns the headlights on and off.  The interior lights, marker lights, tail lights, and instrument lights come on as soon as the model is powered up.
• Channel 6.1:  Winch.  A three-position switch controls the winch.  Oddly, spooling in and out cannot be controlled independently.  Instead, the controller alternates between in and out.
• Channel 6.2:  Ramps.  A three-position switch controls the trailer ramps.
• The cooling fan runs off 12V directly from the battery so it begins spinning as soon as the battery is connected even if the model has not been powered on.
  

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