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August 30th, 2021 Leave a comment Go to comments

Model of a modern Russian amphibious armored personnel carrier.


Completion date: 30/08/2021
Power: electric (Power Functions)
Remote control: SBrick
Dimensions: length 59 studs / width 21 studs / height 24 studs
Weight: 2.47 kg
Suspension: double wishbone independent
Propulsion: 4 x PF L motor via a 3-speed remotely controlled sequential transmission on all wheels
Motors: 4 x PF L, 2 x PF Servo, 6 x PF M, 2 x Micromotor

My last year’s positive experience with making LEGO builds float using XPS has prompted me to think of an amphibious vehicle. I’ve started looking at some personnel carriers, because these combine amphibious properties with multiple axles and complex suspension systems, and I have ended up browsing the Russian designs because there are just so many. While many APCs look quite clunky, there was one that caught my eye: the BTR-80. Introduced in 1986, it’s still a reasonably modern machine operated by nearly 40 countries worldwide. I liked its shape and I liked the incredible amount of details on the exterior.

Tests with early chassis and XPS inserts have revealed that the relatively narrow model with heavy electronics located on top is very unstable in water and that its draught is quite deep, so deep that it endangers the electronics and the metal springs in suspension’s shock absorbers. So I’ve removed the inserts, given up on the model being amphibious, and went on to fill the space in the chassis with motors and mechanics. In the end this medium-sized model included 14 motors and 11 motorized functions:

  • 8×8 drive with full independent suspension (4 x PF L motor)
  • steering of the two front axles at various radii (PF Servo)
  • 4-speed sequential transmission, with only the upper 3 speeds used due to PF Servo only having 3 positions (PF Servo)
  • remotely opened side doors, independently left and right (2 x PF M motor)
  • remotely controlled turret traverse and gun elevation (2 x PF M motor)
  • remotely panned and tilted searchlight (2 x Micromotor)
  • remotely controlled front winch (PF M motor)
  • switch-operated two rear propellers (PF M motor)

In short, the model was possibly my densest build ever, with meters of cables and with the entire inside taken up by motors and mechanisms as the bodywork was just 2 plates thick. My goal was to keep the model agile despite all this complexity, with a well working suspension, and also to make the doors open up like the real ones. The BTR-80’s distinctive feature are doors that are located on sides and open as two separate halves: the upper half opens towards the front to provide protection for soldiers exiting the vehicle while the lower half opens downwards to act as a simple ramp. All these goals were achieved, in part thanks to the powerful propulsion system consisting of 4 hard-coupled PF L motors (powered from two LEGO 8878 batteries, two motors per battery), but also thanks to the transmission which finally produced reasonable gear ratio when combined with the rest of the drivetrain – the three speeds varied a lot and changing them actually made sense, even if I almost never used the 1st speed due to abundance of power. The model had enough power to drive over a series of 1 stud tall obstacles on 3rd speed without slowing down. It also had a reasonable ground clearance thanks to the use of the old steering arms, which allowed to keep the suspension arms only 1 stud apart rather than 3 studs apart. With exception of a single spot between the third and fourth axle, the ground clearance almost reached 3 studs all under the chassis. The downside was that the model was quite rear-heavy, and the fourth axle was visibly sagging under weight, even though it was fitted with double shock absorbers, unlike all the other axles.

The accuracy of the model has fallen victim to the functionality, unfortunately, as it become apparent very early that the model is too short to house batteries, drive motors, transmission and the PF Servo motor controlling the transmission. I have chosen to sacrifice the accuracy by moving the upper glacis plate forward and by simplifying the front end. Two issues have prevented me from using complex body shapes. First, the light bluish gray color of the body made even the tiniest gap between plates look like the Grand Canyon, and second, the entire bodywork was just 2 plates thick because there was no room inside the model for it to reach deeper. Therefore almost all of the bodywork had to rely on plates and tiles, without any fancy SNOT techniques. This forced me to stick to the available shapes of the wedge plates and to shape the bodywork accordingly, so that the gaps between the plates would be minimal. The front end has especially suffered as result, because it just looks wrong. This is especially evident in the upper and lower glacis plate, which join to form a sharp edge in the real APC, but are separated by a thick layer of parts in my model. This was forced by the shapes of the wedge plates on the sides – there are simply no plates with angles that are closer to the original ones – and by the front winch, which required some reinforced structure in the front, it couldn’t just go out through a gap between the plates.

Finally, the body color was also a problem because it was impossible to build the model only with brand new, non-yellowed light bluish gray pieces. It therefore mixed pieces at various stages of yellowing, and I wish I could say that this was done deliberately to simulate weathering or some camo pattern, but the truth is that I was just too tired and I didn’t have enough money to ensure that every single piece in the model is factory-new. The model relied on third-party solutions to a large degree, too: it used tires by RC4WD, multiple SBricks and a high-powered Brickstuff LED for the searchlight (but only because to my surprise it proved impossible to push the LEGO LED through the small Technic turntable).

In the end, the model proved an interesting exercise in making functions fit, and it performed very well given its weight and the complexity of the drivetrain, but at the same time the accuracy has been sacrificed and so was being amphibious, which was the starting point of the entire project.

Work in progress photos:

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Media coverage:

The LEGO Car Blog


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