Brick Experiment Channel's LEGO-powered Submarine 5.0 tackles two different underwater control problems with two different mechanical systems. A 400-gram sliding weight changes the craft's pitch, while a pump-driven 50 ml ballast bag adjusts buoyancy. The result is a remote-controlled experimental vehicle that combines LEGO Power Functions hardware with an acrylic pressure hull, sensors and custom electronics.

The project is especially interesting because it treats LEGO Technic as part of a larger engineering system. LEGO motors and mechanical components do real work, but they operate alongside waterproof structures, non-LEGO propellers, a microcontroller and measured ballast. Pool and river tests then reveal how those choices behave away from the workbench.

Video by Brick Experiment Channel. All video rights belong to the original creator.

Featured thumbnail is from the original YouTube video by Brick Experiment Channel. All thumbnail rights belong to the original creator.

Moving weight gives Submarine 5.0 direct pitch control

A submarine needs to control both where it sits in the water and which direction its nose points. Submarine 5.0 separates those jobs. The internal moving weight consists of 400 grams of steel washer plates. Shifting that mass forward moves the centre of gravity toward the bow and encourages a downward pitch; moving it aft has the opposite effect.

This approach is valuable for LEGO engineering because the mechanism can remain inside the dry hull. It does not need an external control surface to create the initial attitude change. The design turns a familiar Technic challenge, moving a carriage accurately along a constrained path, into a practical underwater control system. It also makes weight placement an active function rather than a one-time balancing decision.

A pumped ballast system changes buoyancy

The second major addition is a water ballast system built around a modified Kamoer NKP peristaltic pump and a flexible 50 ml animal IV bag. A LEGO Power Functions XL motor drives the pump. Moving water into or out of the bag changes the craft's effective buoyancy, allowing it to descend or rise without relying only on forward motion.

Peristaltic pumping is a clever fit for the job because the fluid stays inside flexible tubing while the pump acts from the outside. In a compact experimental submarine, that helps separate the water path from the mechanism that drives it. The system also demonstrates an important MOC principle: a specialised non-LEGO component can solve one difficult physical constraint while the surrounding LEGO mechanism supplies power, structure and experimentation.

Power Functions and sensors share a crowded hull

The 2.95 kg craft uses three LEGO Power Functions M-motors and one Power Functions XL-motor. Two handed 55 mm four-blade propellers provide thrust, with magnetic coupling helping transfer rotation through the sealed arrangement. The power source is a LEGO Rechargeable Battery Box 9V, while a DRV8833 motor driver manages motor control.

An Arduino Nano ESP32 acts as the onboard computer. A Honeywell pressure sensor supplies depth-related information, and an MPU-6050 six-axis gyroscope and accelerometer measures movement and orientation. Those components turn the submarine from a purely mechanical model into a monitored control platform. A GoPro 8 adds onboard footage, making the tests useful both as demonstrations and as diagnostic runs.

Balance is as important as propulsion

The transparent acrylic cylinder measures 250 by 120 by 3 mm, with a 12 cm plastic half-ball forming the rounded nose. Inside, 1.35 kg of tungsten pellets supplies extra mass. Tungsten packs substantial weight into a small volume, which is useful when the hull must reach near-neutral buoyancy without sacrificing all of its internal space.

Placing heavy material low also helps stability by lowering the centre of gravity. That passive balance works together with the active sliding weight: one keeps the craft settled around its roll axis, while the other deliberately changes pitch. For Technic builders, the lesson is clear. Motors cannot correct every problem efficiently; careful mass distribution should make the model naturally cooperative before automation begins.

Pool and river tests expose different demands

The video moves from construction to a swimming-pool test and then to a small river. The craft is listed with a 1.5 m test depth, a meaningful environment for checking sealing, trim and radio-controlled handling. A pool offers relatively still water and visible boundaries, while a river introduces current, less predictable movement and a more demanding recovery situation.

Testing in stages is one of the strongest ideas builders can take from the project. A complex MOC should first prove its individual mechanisms, then operate in a controlled environment, and only after that face realistic conditions. Submarine 5.0 is not simply a finished display model; it is the fifth iteration of a system that has previously explored syringe ballast, magnetic coupling, compressor-driven ballast and automatic depth control.

Final Thoughts

LEGO-powered Submarine 5.0 stands out because its newest systems address specific physical problems. The moving steel mass controls pitch, the pumped bag controls buoyancy, low-mounted tungsten supports stability, and the sensor package observes the craft's motion. Each choice has a clear engineering role.

For LEGO Technic and MOC builders, the project is a compelling example of iteration. It shows how a model can evolve by isolating one weakness at a time, adding a mechanism, and testing the full system under more demanding conditions. The result is part LEGO machine, part experimental vehicle and an unusually practical lesson in underwater control.

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Disclosure: This article was created with AI assistance and reviewed as an independent editorial spotlight. The featured video and thumbnail belong to their original creator.