Sariel.pl

Model of the KZKT 7428 Rusich tank transporter. Features remote control over Bluetooth using the NXT unit, remotely locked fifth wheel and independent trailer with working outriggers and ramp.  

Datasheet:

Completion date: 03/05/2013
Power: electric (Power Functions / NXT)
Dimensions:
truck: length 85 studs / width 26 studs / height 27 studs
trailer: length 134 studs / width: 24 studs / height: 25 studs
Weight: truck: 3.357 kg, trailer: 2.538 kg
Suspension: full independent
Propulsion: 1 x NXT motor geared 7:1
Motors: truck: 3 x NXT motor, trailer: 2 x PF Medium motor

KZKT 7428 Rusich is one of many Soviet-built 8×8 prime movers, designed to tow loads up to 70 tons over any terrain, under any weather conditions. It’s powered by a 650 HP engine with a pre-heating system that allows it to operate even in -50°C (AKA “Siberian summer”), and makes it powerful enough to tow glaciers around. I have discovered Rusich after I’ve decided to build the K2 Black Panther tank, and the two were designed to operate together from the very beginning.

Pictured below: the Rusich radiating awesomeness

The truck was fitted with a full independent suspension and 8×8 drive, with steering on axles #1 and #2. To compensate for the very heavy, protruding cabin, the first axle was fitted with 6 hardest shock absorbers, the second with 4, the third with just 2, and the fourth with 4 again. The body was studfull, sitting on a studless chassis. This resulted in a good look and a compact, functional chassis, but also meant putting a lot of weight on top of a body frame that was prone to some bending, making the truck’s front end sag a little. The independent suspension was not necessarily the best choice for a model that front-heavy, but I believe it supported the weight properly and kept the drivetrain relatively unburdened.

The truck was able to drive well on its own, although it clearly had poor grip on two rear axles. The handling was much improved with the trailer connected.

The trailer, while simple, proved challenging for purely structural reasons. It was basically a 1 meter long structure supposed to carry a 2.5 kg heavy tank model while supported on its ends. That meant a lot of structural stress, and even though the trailer’s “deck” was built around two rails of solid Technic bricks 2×2 studs thick, increased to 2×3 studs (that is 16mm x 24 mm) with addition of tiles of top and plates on bottom, it was still bending a little under the tank. The trailer was supposed to operate independently, so it carried its own power supply in form of a Power Functions AAA battery box. It powered lights on the sides of the trailer, the PF Medium motor controlling the rear ramp through a pair of small linear actuators, and another PF Medium motor with another pair of small linear actuators acting as parking outriggers in front. The ramp was supplemented with sections of rubber axle joiners, taking part of its surface, to improve tank’s grip – still, it proved practically impossible for the tank to climb up. The outriggers, on the other hand, worked perfectly well, and proved strong enough to lift the trailer’s front even with the tank sitting on it.

The trailer was intended to be coupled and uncoupled remotely, so its only connection to the truck was a short studless boom that could rotate, allowing the truck to turn with the trailer. The boom went into an opening in the truck’s chassis going from the back to between axles #3 and #4, where it was secured in place by a simple studless lock. The lock was operated by the truck’s third NXT motor, using a linear clutch and a worm gear to prevent yielding. It proved to work very well, and the coupling procedure was: to back the truck up aiming at the trailer’s boom, stop the truck, lift the trailer’s outriggers until the boom rested on top of the truck, lock the boom and drive off.

The whole “tandem” was rather complex when it came to control system and power supply. I wanted both the truck and the trailer to be able to operate simultaneously with the tank, which used three PF channels. So, I decided to use the fourth and last PF channel to control the trailer, making the truck fully NXT-operated. A single NXT unit went into the engine bay of the truck, where – fully enclosed – it would be connected to my PC over a Bluetooth link, and steered with a regular control pad. The drive and steering were both controlled proportionally. The trailer, which was supposed to be a stand-alone unit, carried its own power supply and a single PF IR receiver. Thus, it could be controlled at any point in one of two ways: directly from the PF remote used to control the tank, by just switching to a different channel, or through the NXT IR Link sensor sitting in the truck’s rear fuel tank. The sensor sent commands to the receiver sitting on top of the trailer’s boom, well within its range, and it was operated from the same control pad as the rest of the truck. It provided a very convenient truck/trailer control system, with a single pad allowing to control both at any moment and practically any range. The PF remotes were only needed to operate the tank, and could also be used at ant moment.

There was a wide combination of power sources used; the truck was powered primarily by the NXT unit, but also housed a small 9V battery box that provided power for its lights. I was at one point considering motorizing the truck’s windshield wipers, but it’s roof was too thin to allow both this and the system of lights on top of the cabin. The trailer, as mentioned above, carried one PF AAA battery box inside. Finally, the tank was powered by two rechargeable PF batteries, one for the propulsion system and one for everything else.

It should be noted that the truck and trailer were largely similar to my model of the SLT Faun tank transporter from 2008. However, I believe they have vastly improved over it.

The truck and trailer were both plagued by a number of problems resulting from large sizes and loads involved.As it turned out, the worst problem was the lack of easy battery replacement option in the truck’s NXT unit. Even with high-end batteries, it made the truck nearly run out of power by the end of the filming, and it was barely able to tow anything, even though it easily tows a tank on the trailer at the video’s beginning (0:22).  Using the rechargeable batteries for NXT would probably provide a solution to this, but they are very rare, expensive, and make the NXT unit even bigger.

In the end I was happy primarily with having finished the model, which took plenty of time and parts to build. It turned out essentially successful, with all functions working as intended, even if slow and strained. Its main goal was to find a way to play with multiple roughly same-scale models at the same time, and this is where it performed flawlessly. I have always been deeply impressed when seeing one model carried and then deployed from another on various RC models shows, and it’s been my longtime goal to do the same with LEGO models, without compromising their size, functionality, or their amount of details. In this, I consider Rusich a definite success.

Gaming pad control program:

#pragma config(Sensor, S4, HTIRL, sensorI2CCustom) 
#include "drivers/HTIRL-driver.h" 
#include "JoystickDriver.c" 
tPFmotor Ramp = pfmotor_S4_C3_A; 
tPFmotor Outriggers = pfmotor_S4_C3_B; 

task main() 
{ 
  bMotorReflected[motorA] = false; 
  bMotorReflected[motorB] = false; 
  bMotorReflected[motorC] = false; 
  while(true) 
  { 
    getJoystickSettings(joystick); 
    motor[motorA] = 0; 
    motor[motorB] = 0; 
    motor[motorA] = joystick.joy1_y1 / 1.28; 
    motor[motorB] = joystick.joy1_y2 / 1.28; 
    nxtDisplayCenteredTextLine(0, "BATTERY: %3.1fV", nImmediateBatteryLevel / (float) 1000); 
    nxtDisplayTextLine(2, "A: %d", motor[motorA]); 
    nxtDisplayTextLine(3, "B: %d", motor[motorB]); 

    if(joy1Btn(1) == 1) 
      motor[motorC] = -100; 
    else if(joy1Btn(3) == 1) 
      motor[motorC] = 100; 
    else 
      motor[motorC] = 0; 

    if(joy1Btn(6) == 1) 
    { 
      PFMotor(Ramp, 7); 
      nxtDisplayCenteredTextLine(5, "Ramp >>"); 
    } 
    else if(joy1Btn(8) == 1) 
    { 
      PFMotor(Ramp, -7); 
      nxtDisplayCenteredTextLine(5, "Ramp <<"); 
    } 
    else if(joy1Btn(5) == 1) 
    { 
      PFMotor(Outriggers, 7); 
      nxtDisplayCenteredTextLine(5, "Outriggers >>"); 
    } 
    else if(joy1Btn(7) == 1) 
    { 
      PFMotor(Outriggers, -7); 
      nxtDisplayCenteredTextLine(5, "Outriggers <<"); 
    } 
    else 
    { 
      PFMotor(Ramp, 0); 
      PFMotor(Outriggers, 0); 
      nxtDisplayCenteredTextLine(5, "Idle"); 
    } 
  } 
} 
									

Work in progress photos:

Photos:

Video:

Media coverage:

The LEGO Car Blog, Yiharuablog