Mineral Oil Tank Rover Design

I need an engineer to produce a design-only blueprint and bill of materials for a small, remotely controlled rover that moves inside a tank of mineral oil. My team will build it.

The challenge: it must move in oil without creating bubbles or disturbing the oil. That means no exposed propellers, and no air or other fluid entering the oil. Buoyancy alone only moves it up and down, so I want your recommendation for controlled sideways movement and position holding. My idea is about 6 enclosed, ducted thrusters on a rounded hull, but I'm open to better.

Targets (confirm or challenge with calculations):

Size: 20 × 20 × 23 cm maximum
Mass: 3.0 kg or less including payload (bare rover 2.2 kg, about 0.6 kg reserved for future sensors)
Oil: 5–40 cSt, 5–70°C; rated for 3 bar absolute
Battery preferred; wireless preferred, but assess feasibility inside a steel tank
E-stop and float-up recovery; 60 minutes continuous run
Build BOM ceiling: ₹6,50,000

Deliverables: concept and calculations, 3D CAD and drawings, electrical design, costed BOM, test plan.

Terms: 3–4 weeks, fixed price paid by milestone, full IP transfer, NDA before detailed specs.

Please answer in your proposal:

How will your design move laterally without exposed propellers, bubbles or foreign fluid in the oil?
How would you size thrust in 5–40 cSt oil?
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Your hour estimate and start date?