Underwater high power motors


I am trying to build a custom underwater vehicle, its propulsion method is a bit particular. I need underwater motors with a high torque (around 8-10Nm) and with encoders to control the position. Another issue is that i need the motors to withstand high pressure, almost 30 atm. I have been looking for ideas and I have seen the oil filled and pressure compensation systems. I wonder if anyone knows some company that could help me to continue with this investigation. I have tried to put a mechanical seal to the shaft but it overheat the electric motor and stops, another option would be to try magnetic?

Thanks in advance. :smile:

What do you mean you need to control the position?
Do you need to move the direction that the motor points?
Or do you need to know the speed?
I suggest you use brushless motors like the T200 or T500. Don’t try to use waterproof motors using lip seals. They will add drag the deeper you go and they need power to overcome the initial friction. The seals can also wear and leak.
I abandoned my design that used rotating thrusters and re-designed to avoid the problems. There were other advantages to use the T200 such as being shrouded and less likely to foul.
Contact me private (anyone) for a pdf of my ROV design history.
This is my original side thruster construction. The thruster motor is outside the ROV, the rotator motor is inside. Bothe assemblies require seals.

Hi German -
Such motors do exist, but they often cost 10s of thousands of dollars! You may be able to use an underwater servo, but the torque you need is fairly high. An M200 with a 16 or20:1 gear reduction may also be able to meet your needs - it might be possible to use with an Odrive and (potted) magnetic encoder sensor - important to set current limits correctly!

If you mean servomotors, just use brushless servos filled with mineral oil. You might have to replace the potentiometer with a magnetic position type to make it last forever. With mineral oil in the servo body, there’s no void for water to invade.

Thanks Peter,

I need to have an encoder to measure the angular position of the motor shaft since I use a different propulsion method than normal ROVs, not by thrusters but by thrust propulsion, as we humans swim.
I already did the tests with the seals and it is true that the power to overcome the initial friction is great, I have already discarded that technique.

I will look at these motors you mention but I think they do not come with encoders, I will consider the option of including them but I do not know how difficult it is.

Thanks for the reply Anthony,

I have searched in the internet and I havent been able to find a company that sells them, do you know any company that could sell them? Despite the price I want to see them.
I have bought the servos and I am testing. What you are suggesting is to add an encoder to the M200? Thats interesting, I will take a look.

I need a servo to rotate the Ping Sonar over 90 degrees. It is not simple.
These would work but still need to be enclosed with a shaft seal.

Because they are high torque and geared they will not be bothered by the drag of a shaft seal.
They may not last long if driven continuously.

Be careful; encoder might mean speed encoder, not absolute position.

If you want to stay away from seals you need to go to very expensive commercial servos.
I have thought of hydraulic actuators but they still have shaft seals to deal with.
See my discussion on the subject Rotating Shaft Seals - General Discussion - Blue Robotics Community Forums
Magnetic coupling has a problem of high pressure on a thin separator wall that may have a large area.
You may find something here Waterproof Actuators | Underwater, Subsea Actuators for ROV, UUV, AUV (unmannedsystemstechnology.com)
If you come up with a simple cheap solution please let me know.

This motor is quite capable, but I believe it costs at least $30,000 US…
Goldline-Submersible_DataSheet_Final.pdf (1.7 MB)

Thanks Anthony, that is actually too expensive for my budget, however I have found these actuators, I put here the links so if someone is looking for something similar. I think they can be useful for my application since I dont need high RPM but I have to check somethings.

I also was thinking of hydraulic actuators, I will take a look on the Stingray Class but I think I will have a similar problem with high current and high temperature if I add a seal.

Sorry, I was talking about absolute or relative position.

I think my next try will be magnetic coupling, I will update if I get something working.
Thanks for the advice.