With the rapid expansion of underwater robots, unmanned surface vehicles, and underwater thrusters in scientific research, marine inspection, and recreational applications, the motor—being the core power component—has become a critical factor in system performance. Among various motor types, brushless motors have almost become the standard configuration for underwater thrusters. So why must underwater thrusters use brushless motors? This article provides a systematic explanation from the perspectives of structure, operating environment, and real-world performance.
Extreme Requirements of the Underwater Operating Environment
Underwater thrusters operate for long periods in high-humidity or fully submerged conditions, while also withstanding water pressure, corrosive media, and continuous load operation. Such harsh environments place extremely high demands on a motor’s sealing capability, operational stability, and service life. If a motor generates excessive wear or sparks during operation, efficiency drops and the risk of water ingress and failure increases significantly.
Brushless Motor Structure Is Better Suited for Waterproof Sealing
Traditional brushed motors rely on physical contact between brushes and the commutator for current switching. This structure inevitably causes wear and sparking and requires a dry internal environment. Brushless motors, by contrast, use electronic commutation and contain no brushes, greatly reducing mechanical wear and making them far easier to fully seal or encapsulate.
Because of this structural advantage, brushless motors can more easily achieve high waterproof protection levels in underwater thrusters, significantly lowering the risk of water intrusion and improving long-term reliability.
Higher Efficiency Means Longer Endurance
Most underwater devices are powered by batteries, making energy efficiency a critical concern. Due to reduced friction losses and higher electromagnetic efficiency, brushless motors can convert more electrical energy into effective thrust under the same power conditions. Compared with brushed motors, brushless motors generate less heat and consume less energy, making them ideal for underwater thrusters that must operate continuously for extended periods.
Stable Output for Precise Propulsion and Control
Underwater thrusters must not only provide sufficient thrust but also enable precise control. Brushless motors, when paired with appropriate controllers, allow accurate regulation of speed and torque, performing especially well during low-speed propulsion, hovering, and fine attitude adjustments. This stable and linear output characteristic is difficult for brushed motors to maintain over long operating periods.
For underwater robots and ROVs, propulsion precision directly affects operational quality and safety, giving brushless motors a clear advantage.
Longer Service Life and Lower Maintenance Costs
In underwater environments, motor failure often leads to high repair or replacement costs. Since brushless motors eliminate brush wear, their service life is significantly longer than that of brushed motors, and maintenance requirements are much lower. This makes them particularly suitable for sealed, hard-to-access underwater propulsion systems.
From a long-term cost perspective, although brushless motors may require higher initial investment, they offer superior overall cost-effectiveness.
Better Adaptation to High-Torque, Low-Speed Conditions
Water has far greater resistance than air, meaning underwater thrusters require high torque during startup and low-speed operation. Brushless motors, with proper control strategies, can deliver stable high torque at low speeds, better matching propeller hydrodynamic characteristics and avoiding slippage or efficiency loss.
Conclusion
In summary, the reason underwater thrusters must use brushless motors is not due to a single factor, but the combined advantages of superior waterproof sealing, higher efficiency, precise control, long service life, and overall reliability. For any propulsion system that must operate stably underwater over long periods, brushless motors are currently the most mature and dependable choice—and they will continue to be the dominant direction for underwater power systems in the future.