In the design and operation of underwater unmanned vehicles (UUVs), the propulsion system is a critical module that directly affects speed, endurance, and reliability. In modern UUV propulsion systems, brushless DC motors (BLDC motors) have become the mainstream choice. Understanding and selecting the right motor parameters is essential for optimizing overall performance.
Basic Requirements for UUV Motors
Compared with aerial or land-based vehicles, UUVs operate in more challenging environments and require motors that can:
Operate reliably underwater for extended periods
Maintain good sealing and corrosion resistance
Provide stable torque to handle water resistance variations
Operate efficiently to reduce battery consumption
Offer high reliability with minimal maintenance
These requirements make brushless motors the preferred solution for UUV propulsion systems.
Key Parameters of Common Brushless Motors
When selecting a brushless motor for a UUV, the following parameters are critical.
Rated Voltage
The motor’s rated voltage should match the battery system. Common voltage levels include:
12V
24V
36V
48V
Higher voltage allows for lower current at the same power, reducing wiring losses, but increases insulation and driver requirements.
Rated Power
Motor power directly affects propulsion capability:
Small reconnaissance UUVs: 50–300W
Medium operational UUVs: 300–1500W
Large or deep-sea UUVs: 2kW or higher
Power selection should consider mission requirements, propeller efficiency, and battery capacity.
KV Value (Motor Constant)
KV indicates the motor’s RPM per volt at no load. UUV propulsion typically favors low KV, high torque designs. Common KV ranges are 100–1000 KV. Higher KV values may increase speed but reduce efficiency in high-resistance underwater conditions.
Maximum RPM
The motor’s maximum RPM must match the propeller’s diameter and pitch. Typical ranges for UUVs are 3000–8000 RPM, balancing efficiency, noise, and bearing life.
Torque
Underwater propulsion faces significant resistance, so sufficient torque is crucial. Standard BLDC motors for UUVs provide rated torque from 0.1–5 N·m, depending on propeller size and load conditions.
Protection and Structural Parameters
Waterproof Rating
BLDC motors for UUVs require high protection ratings:
IP67: short-term immersion
IP68: long-term underwater operation
For deep-sea applications, pressure resistance is as important as waterproofing.
Material and Corrosion Resistance
Motor housings and shafts typically use:
Stainless steel
Anodized aluminum alloys
Titanium (for high-end applications)
These materials enhance resistance to seawater corrosion and extend service life.
Efficiency and Thermal Management
Efficiency
High efficiency translates into longer endurance. BLDC motors in UUVs typically achieve 80–90% efficiency, with optimized designs exceeding this.
Temperature Rise and Cooling
While water aids heat dissipation, sealed designs can limit thermal transfer. It is important to consider allowable temperature rise and cooling design when selecting a motor.
Comprehensive Selection Considerations
Motor parameters should not be considered in isolation. Selection must account for:
Mission type (patrol, inspection, towing)
Water depth and quality
Propeller type and efficiency
Battery capacity and desired endurance
System reliability and maintenance constraints
Only a well-matched system can fully leverage the performance of brushless motors.
Conclusion: Parameters Define Performance, Matching Determines Success
In summary, common brushless motor parameters for UUV propulsion systems focus on voltage, power, KV value, torque, waterproofing, and efficiency. Understanding these parameters and selecting a motor that matches operational conditions is key to ensuring stable, high-performance underwater operations.