STEM ROV : Simple DIY Thruster based on 360 Brushed Motor

This article describes how to make a simple waterproof thruster using 360 brushed motor with simple materials.

This is a low-cost solution with good propulsion power. It provides thruster options for DIY boats in primary and junior high schools or making thrusters for STEMPVC ROVs. Its simple DIY process allows students to experience the fun of making waterproof thrusters by themselves!! Ipanema STEM ROV Kit also adopts this simple solution.

Brushed motors are much cheaper than brushless ones. In terms of motor control, the brushless motor needs to be controlled by an so-called ESC (Electronic Speed Controller), while the brushed motors can use the cheap L298N series motor driver which is popular in many schools.

Special attention is that the torque of the brushed motor is proportional to the curren at a specific operating voltage. The resistance of water is much higher than that of air, so the current consumption of the motor in water is often several times or even dozens of times that of the air. After making a simple thruster with a 12000 rpm brushed motor, the loading current in the air is about 0.27A, but the current consumption in water can reach more than 3.5A!!

The motors used in underwater thrusters are not high in speed. You can recall the experience of riding a bicycle. You can switch to a high gear when riding a bicycle on flat ground, and usually switch to a low gear when you encounter a climb, which saves effort and even time.

Devoted to simple DIY underwater thruster, ROV MAKER provides RS-360 ENJOY Brushed Motor, which is a low-speed motor with a speed of about 5000RPM. With dedicated STEM ROV Blade Pair, the current consumption is about 1.7A/15V and 12.1/A14V . The L298N-based motor drives currently available in the market has an operating current of about 1A-2A. You can choose the motor drive with an operating current of up to 2A.

STEM ROV Blade Pair, is a two-bladed high-speed paddle pair, including one CW and one CCW blade . The advantage of using STEM ROV Blade Pair is that the forward and reverse rotation of the two simple thrusters can be used to achieve the steering of the ship, saving the use of the rudder.

 

In the CFD (Computational Fluid Dynamics )simulation, it can be found that blades of STEM ROV Blade Pair  can provide a concentrated and stable thrust in the water even without duct.

motor drive shaft is required between the brushed motor and the blade. ROV MAKER provides Aluminum-alloy Motor Drive Shaft. The advantage of aluminum alloy is that it is more resistant to seawater than brass, its weight is light, and it has little resistance to the start of the brushed motor. One end has a 2.3mm hole diameter and can be directly inserted by the carbon brush motor shaft. The other end is a machined M4 screw hole, which can be used to fix the blade by M4 screws. M3x3 setscrews can be used to make the motors and blades keeps tight on both side of  Aluminum-alloy Motor Drive Shaft.

The basic concept of Simple DIY Thruster based on 360 Brushed Motor is to use the film box as the thruster shell, and the brushed motor is placed in it. Both ends of the film box are filled with special butter to achieve waterproof effect. If it is on the general water surface or two or three meters underwater, such waterproof treatment is sufficient. This is a well-known way on the Internet. It is suitable for elementary and junior high schools students to implement . The main steps are

• Drill 2.4mm OD holes on both ends of the film box
• Seal the holes for heat dissipation on the surface of the 360 brushed  motor  with insulating tape.
• Solder the relevant wires to the two poles of the brushed motor
• Both ends of the motor are coated with special butter to seal the coin box

For the special butter, please refer to the Wax ring, One  Wax ring, can make many simple DIY Thrusters based on 360 Brushed Motor.

For a detailed assembly introduction, please refer to the following video

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