The main problem in thruster design is how to isolate engine from water. There are three solutions used to keep engines away from water:

• O-ring
• Rotary shaft seal
• Magnetic coupling

The best and more complicated is solution 3. The engine is perfectly isolated from water because it is connected to the propeller using magnetic coupler.
Solutions 2 and 3 are similar.

The open/close manipulator is useful tool to retrieve small objects or attach a line to objects located underwater.

The jaws of are driven by the electric screwdriver. Using electric screwdriver has many advantages:

• Easy available
• Cheap, cost about 5€.
• Powerful - 2.4Nm
• Planetary gearbox (low quality)

Introduction

A brushless DC motor is electric engine where the stator is a classic 3 phase stator and the rotor has surface mounted permanent magnets. It is equivalent to a reversed DC commutator motor, in which the magnet rotates while the conductors remain stationary. BLDC motor has no commutator and brushes, it requires electronic control for operation. They often have external position sensors used by control unit, but sensorless control is also possible.