Currently, underwater brushless motors are mainly categorized into two structural types: inner rotor and outer rotor designs. Each type has its own merits, and selection can be made based on equipment requirements, installation space, load characteristics and operating environments.

Inner Rotor Underwater Motors: A Mature and Reliable Basic Solution

The core components of inner rotor motors are enclosed inside a stationary housing, with dynamic sealing only required at the output shaft. Featuring proven sealing design and high reliability, this is currently the most widely adopted power solution for underwater applications.

Its key advantages are as follows:
• Mature structure with waterproof solutions validated by long-term market application;
• Stable operation, fast control response and wide speed range;
• Concentrated sealing points, well-established production processes and obvious cost advantages;
• Compact radial dimensions, suitable for equipment with limited installation space.

Nevertheless, as underwater equipment evolves toward miniaturization, higher thrust and longer service life, conventional inner rotor solutions face limitations. They deliver limited output torque under the same volume. Additional reduction gearboxes are generally required for high-load applications, which results in complicated structures, larger overall size and higher maintenance costs.

IP68 Outer Rotor Underwater Motors: An Upgraded High-Torque Direct-Drive Solution

Outer rotor motors feature inherent high torque density, enabling low-speed, high-thrust direct drive without extra reduction mechanisms. They are ideal for highly integrated underwater equipment operating under heavy loads.

However, outer rotor motors have multiple dynamic sealing interfaces. Achieving long-term dynamic IP68 protection has long been a key technical challenge within the industry.

To tackle this technical difficulty, our company has developed a fully sealed outer rotor brushless motor solution. While retaining the outer rotor’s strengths of high torque and compact structure, multi-layer sealing design is adopted to realize dynamic IP68 protection for a fully sealed dry chamber. This meets the demands of long-term reliable operation for pool cleaning robots and deep-water equipment.

IP68 Outer Rotor Fully Sealed Waterproof Core Technology

This solution adopts a multi-dimensional protection system:

1. Fully sealed structural design for the complete unit

Adopting a combined sealing structure with upper and lower housings, it meets IP68 protection requirements and supports long-term operation underwater at a depth of 3.5 meters.

2. Integrated watertight wiring design

Potting seal is applied to fix the cable outlet position, effectively preventing moisture from entering the motor interior along the wiring harness.

3. Dual oil seal dynamic sealing system

The output shaft adopts a dual oil seal structure filled with grease in between, which reduces friction loss, extends the service life of oil seals, and improves sealing reliability under rotating dynamic conditions.

4. Multi-layer composite housing sealing structure

Multiple sealing barriers are arranged at housing joints. Radial and axial sealing rings form multi-layer protection to enhance reliability during long-term underwater operation.

Verification under stringent operating conditions to guarantee long-term reliable performance

Targeting the application scenario of pool cleaning robots, we have carried out durability tests in high-concentration chlorinated water environments, with continuous immersed operation under load for 3,000 hours.

Test results show that the motor interior remains dry without water ingress, corrosion or jamming. Torque output and operating performance stay stable, satisfying demands for long-duration continuous operation of residential and commercial pool cleaning robots.

At present, this IP68 fully sealed waterproof structure for outer rotor motors is protected by a national utility model patent. It achieves a technical breakthrough combining outer rotor direct-drive structure + fully sealed dry chamber + dynamic IP68 protection + long-lifetime validation.

How to Select the Suitable Solution?

• Inner rotor underwater motor: Suitable for lightweight, precision shallow-water equipment, with priorities on stability, cost and mature mass production capacity.
• IP68 outer rotor underwater motor: Suitable for equipment requiring high thrust, heavy-load direct drive and long-term deep-water operation. It can effectively reduce system complexity and improve overall unit reliability.

Customization of motor dimensions and performance is available.

CJC has adopted dual technical routes covering inner rotor and outer rotor solutions. We provide customers with one-stop underwater motor solutions ranging from proven basic power systems to high-performance deep-water power units, supporting the continuous upgrading of global underwater equipment.