Magnetic Assembly for Underwater ROV Thruster Coupling

Problem

A UK subsea robotics company needed magnetic couplings for ROV (Remotely Operated Vehicle) thrusters. The coupling transmits torque through a pressure barrier, eliminating shaft seals that fail in deep-water environments.

Requirements:

• Precise torque capacity (12 Nm at 3mm air gap)
• Corrosion resistance for saltwater immersion
• Pressure resistance to 200m depth (20 bar)
• Matched magnet pairs with less than 5% torque variation

Their existing European magnet supplier quoted 12-week lead times and pricing that made the ROV economically unviable for commercial applications.

Solution

We designed a two-part magnetic coupling assembly:

• Drive ring: 8× N42 arc segments bonded into a steel cup
• Driven ring: 8× matching N42 arc segments in aluminum housing
• Each pair magnetically matched using Helmholtz coil testing

Supply chain approach:

• Magnets sourced from Ganzhou (N42, epoxy-coated)
• Arc segments wire-cut to ±0.05 mm
• Assembly and bonding performed at factory
• Pre-shipment torque testing on each coupling pair

Specifications

• Material: NdFeB (N42)
• Shape: Arc segments (45° span) × 8 per ring
• Ring OD: 65 mm, ID: 45 mm, length: 20 mm
• Coating: NiCuNi + epoxy (marine grade)
• Air gap: 3 mm (through PEEK pressure barrier)
• Target torque: 12 Nm ±5%
• Volume: 50 coupling pairs per order

Results

• Coupling torque measured at 12.3 Nm average (within 3% of target).
• All assemblies passed 200m simulated depth pressure testing.
• Cost reduced 28% compared to previous European-sourced couplings.
• Lead time reduced from 12 weeks to 5 weeks including assembly.

Next Steps

Share your coupling geometry, torque requirements, and operating environment. We will provide a feasibility review and torque simulation before quoting.