I am assisting a group of students who are engaged in a project to build an undersea ROV. We need some simple thrusters that are capable of up to 100-meter operating depth. Our motor control system is simple so we want to use brushed DC motors; that way we can control direction with polarity and speed with voltage. The power supply should be in 12 to 24-volt ange. We are having difficulty finding such a thruster.
Please let me know if anyone has something that we can use, or if you know of a source
for this. Thank you very much for any help you can offer.
Hi @Chrisar, welcome to the forum
Brushed motors require an electrically conductive brush to serve as an open contact point between the stator and rotor. To avoid wetting that and corroding the motor it’s necessary to make a water-tight seal around the shaft, which can be practical for cheap RC boat use-cases, but is more challenging for a motor that needs to also be pressure rated.
I suspect there’s not much value in developing a brushed DC motor that can reliably be used to 100m depth, particularly when compared with the efficiency and longevity benefits of a brushless DC motor, combined with the relative ease of waterproofing its electrified components (since there’s no electrical connection between the rotor and stator), and the expense already going into the rest of a vehicle that could make use of an underwater motor.
If your main hope is to maintain a simple control system with a voltage output then you could potentially get or make a board that converts an input voltage into a signal that’s suitable for passing into a brushless DC motor controller, but that shifts complexity to an additional component, likely with some extra expense, so is mostly worth considering for a simplified software experience for the students.
In that vein, our Thruster Commander can be controlled with 0-5V input signals (instead of using the included potentiometers), if that’s of interest, but if you’re building this into an underwater vehicle with its own control system then the costs associated with the nice packaging and connectorised inputs could be avoided by replicating just the functionality you actually need using a microcontroller.
Thank you for the reply. Now it makes sense why all thrusters are brushless. For now we need to get something going quickly and at low cost so that we can apply for additional funding. With this next round of funding we plan to integrate a microcontroller to control brushless thrusters the way they should be.
I briefly looked at the Thruster Commander, and it looks like it may be a suitable solution. I have some questions about using 0 to 5-volt input signals in place of the potentiometers. What is the input voltage to put thrusters in neutral? Would that be 2.5-volts? That would mean changing the input voltage above or below 2.5 volts would change the thrust direction; is this correct?
I also looked at the ECS from Blue Robotics. The thruster direction and speed are controled by a signal between 1100 uS to 1900 uS. I’m assuming these are PWM pulsewidths; is this correct?. What is the PWM frequency typically used?
Let me know what you can. Thank you again, and I appreciate any help you can provide.
Assuming you’re not using the “Steering” input option then yes, 2.5V is the neutral/stopped point, and going above or below that determines the thrust direction.
Yes, our Basic ESC interprets its input signal in terms of PWM pulse-durations
Per the technical details on the product page, the maximum update rate is 400Hz.