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January 24th, 2022 Leave a comment Go to comments

An experimental screw-propelled LEGO model using 3D-printed screws. Features drive and steering.


Completion date: 22/01/2022
Power: electric (LEGO PF)
Remote control: SBrick
Dimensions: length 36 studs / width 18 studs / height 17 studs
Weight: 1.012 kg
Suspension: none
Propulsion: 2 x PF L motor geared 5.25:1
Motors: 2 x PF L motor

ZIL-2906 was developed by USSR as one of several solutions for retrieving Soyuz crew capsules from remote areas where conventional vehicles couldn’t reach. It was propelled by a pair of mirrored screws, which was quite an unusual solution (not a new solution, though – US tractor makers have experimented with this idea earlier). The screws may seem like an odd method of propulsion, but I recommend that you watch deep snow test around 9:09 in the video belowe:

All things considered, using screws for propulsion is a complex issue:

  • pros: they are efficient on soft terrain, snow, sand, mud and can also act as a flotation device and propulsion for an amphibious vehicle
  • cons: they are useless on smooth surfaces (such as ice) because the screws can’t get purchase, they get damaged on rocky terrain, they result in a very shaky ride (since the screws are rigid and can’t adapt to the shape of the obstacle)

In other words, the screws work great under specific conditions but they are useless in others – for example you can drive through deep snow, but not across a frozen river. This prevents them from being versatile and that’s why such a mode of propulsion hasn’t become popular.

My LEGO model was made possible thanks to SaperPL who specializes in designing and 3D-printing LEGO-compatible parts. I’ve ran the idea of building the ZIL-2906 by him and he provided me with two excellent screws. I have done some tests with LEGO-built screws before, but they proved inefficient and unable to handle loads, and seeing as LEGO has already made somewhat similar parts e.g. in the 42112 Concrete Mixer Truck, I thought it made sense to use 3D-printed parts.

The body of the model is simple and has wrong proportions (too short and too tall) because I was trying to make the most of the weather, meaning I only had a few days worth of snowfall and that wasn’t enough to order any pieces, forcing me to build with the pieces I already had. In addition, it turned out – to my surprise – that the modern Technic pieces rarely come in blue, as LEGO sets frequently use different shades of blue, e.g. dark blue, medium azure and so on. In the end, my focus was just on making the model work and look complete.

The resulting model did pretty well in snow but proved too heavy to float in water. I was only able to test it in thin snow (3 cm top), so I can’t exclude the possibility of it being unable to traverse deeper snow, and I was testing on a mostly flat terrain. The model proved sensitive to left/right balance and to changes in traction between the two screws, which would frequently change its direction. Steering was a challenge and turning in place was impossible – instead, the model could drive sideways. I found out that the most efficient way of steering was to operate the screws by turns: so right screw stop, left screw full forward, then left screw stop and right screw full backward. By repeating such operation, it was possible to turn by any number of degrees.

The model was an interesting proof-of-concept, even if it looked hastily put together. I just regret not being able to make it float.


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