NEPTUNE-R — Solar-Powered Autonomous Hydro-Robot (Design + Simulation)

@auth: SeriouslyAndy & Mihnea8848

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This repository documents the design and multi-platform simulation of NEPTUNE-R, a solar-powered autonomous surface robot intended for aquatic purification and oxygenation via a modular microbubble system, with coverage-optimized trajectory planning and a reproducible “digital twin” workflow. :contentReference[oaicite:0]{index=0}

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What this project is

NEPTUNE-R is a concept-to-simulation prototype that combines:

• Mechanical CAD (Fusion 360) for a modular, stable floating platform
• Trajectory planning + optimization (MATLAB R2024a) for full surface coverage
• Dynamic motion visualization + force-based control (Roblox Studio + Lua) for real-time physics validation

The goal is an accessible, zero-emission platform for water quality improvement, supporting sustainable deployment scenarios (e.g., lakes, ponds, aquaculture).

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Key capabilities

Coverage path planning (surface coverage)

Two coverage strategies are implemented and compared:

• Boustrophedon coverage

  • Best for rectangular/irregular water bodies and obstacle-rich environments
  • Uses back-and-forth sweep lines with minimal overlap and obstacle avoidance

• Archimedean spiral

  • Best for circular/open water bodies
  • Smooth motion with fewer turns/direction changes, reducing energy use

Modular architecture

NEPTUNE-R is organized into three functional modules:

1. Energy + propulsion
2. Oxygenation unit (microbubble generator)
3. Control + communication

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System specs (from the simulation model)

Power budget (nominal)

Subsystem	Power	Notes
Propulsion motors	48 W	Two BLDC motors, ~60% duty cycle (avg)
Microbubble generator	22 W	Calibrated from experimental fine-bubble diffuser data
Control + communication	6 W	MCU + sensors
Total average	76 W	Continuous nominal operation
Photovoltaic system	180 W	~21% efficiency @ ~850 W/m² irradiance
Battery storage	24 V, 20 Ah	Lithium-ion pack

Mechanical / design parameters (used in simulations)

Parameter	Value
Total mass	~12–12.5 kg
Hull size (L × W × H)	~1.20 m × 0.80 m × 0.35 m
Buoyancy reserve	~28%

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Simulation workflow (digital twin)

1) Mechanical design (Fusion 360)

• Hull designed for stability and modularity.
• Internal cavities created via negative extrusions to reduce weight while preserving buoyancy.
• Hydrodynamic edge rounding (fillets) to reduce drag and improve safety/maintainability.

2) Trajectory generation (MATLAB)

• Workspace defined as a polygon (lake boundary) with obstacles via polyshape.
• Boustrophedon path generation for systematic sweep coverage.
• Archimedean spiral modeled with:
  • x(θ) = (a + bθ)cos(θ)
  • y(θ) = (a + bθ)sin(θ)
  • Example parameters used: a = 1 m, b = 0.25 m/rad

Dynamics integration uses forward Euler updates with forces in x/y and a discrete timestep.

3) Motion + control validation (Roblox Studio + Lua)

• Real-time physics simulation:
  • buoyancy, drag, inertia, friction
• Force-based control:
  • corrective thrust based on tracking error (proportional/derivative style correction)
• Waypoints are validated against water terrain to avoid land/obstacles.

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Core models / equations used

Obstacle avoidance (repulsive potential field)

A repulsive force term is used around obstacles:

• Fr = kr / d^2
• Example coefficient used: kr = 0.04

Euler forward integration (2D)

Velocity update:

• wx(t+Δt) = wx(t) + (Fx(t)/m)Δt
• wy(t+Δt) = wy(t) + (Fy(t)/m)Δt

Example simulation parameters

Parameter	Value
Rover mass	12 kg
Max propulsion force	15 N
Drag coefficient (Cd)	0.82
Time step (Δt)	0.05 s
Simulation duration	600 s
Spiral pitch (b)	0.25 m/rad

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Reported results (from simulation study)

Coverage + efficiency

• Boustrophedon (50 m × 30 m lake + obstacles):

  • ~97.6% coverage of free area
  • Mission time ~482 s, avg speed ~0.32 m/s
  • Higher turn count (more direction changes)

• Archimedean spiral (circular lake, r = 25 m, no obstacles):

  • ~99.2% coverage
  • Mission time ~438 s, avg speed ~0.34 m/s
  • Far fewer direction changes (~6), ~12% lower energy demand vs Boustrophedon in the compared setup

Oxygenation (simulated DO increase)

• Example DO increases over time (two monitoring points):
  • After 1 hour: ~+0.9 mg/dm³ (shore), ~+1.4 mg/dm³ (center)
  • After 2 hours: ~+1.6 mg/dm³ (shore), ~+2.1 mg/dm³ (center)

Disturbance stability (Roblox-based scenarios)

• Under wind up to ~3 m/s and wave amplitudes up to ~0.25 m:
  • remained upright
  • max tilt ~4.6°
• Long-run scenario indicated small RMS trajectory deviation and moderate energy increase due to dynamic drag.