This is work-in-progress, expect updates to this page.

This is my second RC car in 1/87 scale. It’s a offroad 6WD truck Kamaz 43118.

Again the purpose is to use 3D printed parts as much as possible instead of buying ready-made components.

The main challenges I intend to solve in this project are:

  • All-wheel drive

  • All-wheel suspension

  • Self-made cast flexible tyres

  • Transparent complex shape windows

And the usual RC parts will be present: remote-control over BLE from smartphone and remote, lights etc.

It will have an addon, but I haven’t decided yet what, max goal is a foldable crane.

Prototype

Kamaz 43118 is a soviet/russian offroad 6WD truck with long wheelbase, which is used as a base for all sorts of addons.

Classic Kamaz trucks come with different generations of cabins (K1, K2 and K3).

K1 is the original one, it has round headlamps in the cabin itself, and very flat and low roof.

For K2 the headlamps were moved to bumper and a new higher roof was designed for long-distance trucks.

Somewhere in 90s DAF design team participated and added front plastic bumper, which was developed into K3 cabin, which is still in production today, along with newer models.

All cabins come in long version with a sleeping space behind the seats. K3 generation has a super-high option with huge space above head, and, presumably, 2-level sleeping space.

All sorts or intermediate designs can be found in the wild. Military variants still have round headlights (as it’s military standard for everything from motorcycles to tanks), cranes still use low roof, thick plastic bumper has different designs as well. Aftermarket modifications can combine features from all the generations as well.

Newer generations use cabins licensed from Mercedes (K4, K5), those are nowhere near as recognizable and iconic, so I ignored them.

Interestingly, this old cabin design is tiny compared to modern day long-haul cabins, both in height and depth. This makes it difficult to place large batteries inside, so hiding them will be a challenge.

Drivetrain

The general idea for suspended all-wheel drive is one common shaft along all the axles, each axle is connected to it via worm or similar gear, and the shaft also serves as a suspension pivot.

So there is not really too much suspension going on, lifting any of the wheels will necessarily lift the chassis to half the height.

Proper suspension requires proper U-joints to make a bending driveshaft. This is a challenge for future project.

Worm gears have a big reduction ratio and a lot of friction, which seems potentially unusable for 3D printed gears, so I tried other gear systems as well.

At first I wanted to make hypoid gear set, but could find a way to do it. Hypoid gears have very complicated math behind them and are freakishly complicated to design. In fact, there is no video on YouTube that shows how to do that in Fusion 360 from scratch (or any CAD for that matter), while there almost any other gear type is available.

So I switched to a simpler gear set, crossed helical gears. They are very similar to a worm drive, but reduction ratio is smaller and amount of friction can be somewhat controlled by changing the angle of the contact line.

Steering

Steerable, driven and suspended axle proved to be the most complex part of the drivetrain, and the result is the worst performing component at the moment.

Steering pivots are very far from the wheels, so wheels touch the wheel arches almost immediately, this makes steering radius enormous. Also the short steering axles are a bit loose in the bearings, so the wheels bend and wobble a lot.

The driven steering system was inspired by spring-based shaft couplers on 3D printers, and the part that transfers torque and bends when steering is a steel spring from pogo pins, the same that is used for suspension. It is the most compact design I could invent.

Before I tried a CV-joint of ball-with-pins-type, which is widely used in train models. It needed to be very small for steering axle, so I designed it to be 1mm in diameter, which, to my liking, was too small to be practical. It was difficult to assemble and probably would break too easily under load (though it didn’t break until I replaced it with a new design)

Cabin

The cabin shape looked intimidatingly difficult to design in parametric CAD, so I tried to do it in Blender with mesh-based toolset.

I had almost zero experience with Blender before, so I screwed all the rules about good mesh topology, and the mesh is not a thing I’d be proud to show off. But the geometry and shapes look pretty convincing and recognizable. The model printed without any (big) problems.

Tyres

At the moment tyres are made from tin-based (condensation) silicone. I 3D-print the mold in 2 parts, pour silicone into them, and after a day I get the tyres.

The original idea was to make tyres from polyurethane rubber, but it seems the properties of silicone are good enough already to not bother with additional step of casting urethane into silicone mold.

To be solved: proper coloring or tyres and tight fitting to the rims.

Windows

The plan is to 3D print windows, make a silicone mold from the prints, and cast transparent epoxy into the molds.