Hello,
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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.
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!
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.
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.
Rotary Actuator - Self Compensated - Underwater Actuators
Series Subsea Rotary Actuator
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.
New designs and a wider range of models have enabled the integration of tunnel thrusters into the propulsion systems of most vessel types irrespective of size
Thrustmaster designs and builds tunnel thrusters, azimuthing thrusters and retractable thrusters ranging in power from 26kW to 8.0MW. The company has its headquarters in Houston, Texas and dedicated service centres in Singapore, Dubai, Rotterdam, Rio and China. Thrustmaster was established in and celebrated its 25th anniversary last year by opening a new head office and 18,500m2 manufacturing facility, the largest thruster shop in the world under one roof.
The company manufactures its own components, hydraulic systems, lubrication systems and control panels, building almost everything in Houston. In support of its manufacturing, research and development efforts, the new facility incorporates an internal school, classrooms and a laboratory.
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About 70 per cent of Thrustmaster’s annual US$100 million in sales is exported outside North America. While its thrusters are installed on everything from cruise ships to tugboats, the company has seen much of its business in recent years come from the booming world of dynamically positioned (DP) vessels.
“DP has always been an area we have concentrated on,” said Joe Bekker, founder and president of Thrustmaster. “As the offshore industry moves into deeper waters and mooring systems become uneconomical, they turn more and more to dynamic positioning for drilling equipment and support vessels. At the same time, the fields in shallow waters are getting so congested that anchors can cause problems with undersea infrastructure. We therefore see a continually expanding worldwide thruster market for the next 10 years or so.”
Improved seal design has improved the internal reliability of thrusters. “Historically, seals have always been a bit of a weak point on thrusters,” said Mr Bekker. “Thrusters are filled with high-grade gear oil, which no one wants leaking into the sea. Conversely, neither does anyone want seawater leaking into the gearing. So, for our propeller shafts we use two seals – an inner mechanical seal that makes sure the gear oil stays inside the thruster, and an outer mechanical seal that makes sure seawater doesn’t enter.”
Between the two seals is a cavity that is used to monitor the seals. Any leakage from either seal enters this cavity and is drained to a tank for safe disposal. The mechanical seals are good for the life of the thruster, which is typically 25 to 30 years. In another internal reliability improvement, Thrustmaster recently began a condition monitoring programme, in which instrumentation inside the thrusters allows the operator to monitor the condition of the bearings and gears.
Behind its new manufacturing facility Thrustmaster is constructing a test pond measuring about 137m long, 60m wide and 9m deep where it will perform full-scale testing of large thrusters. “We’ll be studying the bearing load variations and strain of load bearing components of our thrusters in transient conditions with the thruster in the water under full power,” said Mr Bekker. “There is very little literature about this but it is research we feel we must do to make our thrusters totally reliable.”
UK-based Kort Propulsion has established itself in the smaller vessel market with an established range of tunnel thrusters comprising 10 models. Starting from the KT30, with a 406mm diameter tunnel, the range originally extended to the KT250 with an 813mm tunnel and 750mm diameter propeller. Recently the company has launched the KT300 thruster capable of developing 300kW at the propeller with a thrust of 2,700kg. The KT30 to KT170 units have the hydraulic motor fitted in the drive housing directly coupled to the propeller shaft and nose cone assembly. These are fitted and tested prior to delivery. The KT150-200-250 and KT300 models feature a lower gearbox within the tunnel and the hydraulic motor plugged into the input housing inside the vessel. These larger units can also be engine driven through a cardan shaft and right angle gearbox.
A range of ratios is available to suit the engine rating. All models can be supplied with either 210 or 280 bar system pressure and can be integrated with either closed loop or open loop hydraulic systems. There is also a range of electric tunnel thrusters with power ratings from 50 to 300kW.
Utilising its experience in shipbuilding and shiprepair, Kort promotes the reduction of installation and maintenance costs as key factors in the design and development of its thrusters. Tunnels are supplied in standard lengths in mild steel, aluminum or GRP with a stainless steel ring in way of the propeller. All units are supplied with a comprehensive instruction manual and can normally be installed and commissioned without the maker’s attendance.
For control of the thrusters Kort has a range of panels to suit the method of drive. In most cases this is a joystick operated proportional control unit for hydraulic drive. This is a ‘put and stay’ unit which can be integrated with an autopilot if required. Single or multi-station systems can be supplied.
In addition to simply providing off-the-shelf equipment Kort has a wealth of data on both conventional and innovative propulsion systems which enables the company to design and supply fixed pitch propellers up to 4m in diameter or controllable pitch propellers up to 5.3m in diameter. The company refers to its development of a range of small hydraulically driven bow thrust units and high definition propellers and impellers for high speed craft with conventional propulsion as examples of recent bespoke designs.
Schottel, the German manufacturer of azimuthing propulsion and maneouvring systems, designs the propellers and specifies the mechanical components for each tunnel thruster depending on the individual application. The manufacturer offers comprehensive planning advice, including appraisal of hull form, propulsion calculations and installation planning. According to the company, the main advantages of its tunnel thrusters are: compact design, optimised power ratings, accurate matching of reduction ratios for a number of different common drive speeds and the continual introduction of new technologies, including high specification sealing and lubrication systems.
All Schottel transverse thrusters are equipped with a stainless steel wearing ring in the path of the propeller to improve durability, and the tunnel is stiffened to reduce vibration and noise. Further noise reductions are achieved through Schottel’s forward-skewed propeller blades, which are individually engineered for specific customer applications. Where necessary, Schottel thrusters can be resiliently mounted to reduce noise and vibration.
Units are oversized and the propeller tip speed is reduced to minimise propeller load. A high level of gear housing protection is achieved by sandblasting and coating the lower gearboxes with Belzona (Ceramic S-metal), which is extremely resistant to abrasion, cavitation and electrolytic corrosion, says Schottel.
The thrusters can be diesel, hydraulically or electrically driven, and electric prime movers can be included in the Schottel scope of supply. Horizontal or vertical drive applications are possible to ensure an optimised prime mover location and economical, space-saving installation. Thrusters have an L-drive design and power is transmitted to the propeller via a single pair of bevel gears.
The electrical system for pitch control can be adapted to several networks to meet the demands of offshore fleet operators. Switch boxes can be optionally equipped with common dynamic positioning or other interfaces. If required, Schottel can provide a programmable logic controller-based CP transverse thruster system with built-in web server. The equipment provides fault and process value monitoring, with trend views for effective fault analysis, automatic nominal load regulation, depending on actual operating conditions, and an interface to integrated bridge systems.
A new method of tunnel thruster removal and installation developed by Rolls-Royce aims to significantly reduce the need for drydocking and shorten downtimes. “We appreciate that planned or unplanned drydockings are expensive and can take vessels out of revenue-earning service for an extended period,” says Ole Jacob Irgens, Rolls-Royce business development director – services. “We have therefore been investing in developing the techniques and equipment to enable our products to be repaired underwater without the need for drydocking.”
Tunnel thrusters are the first in the group programme to benefit from a patented solution for smoothing underwater exchange. Even in newbuilding projects, Rolls-Royce explains, the normal CP tunnel thruster installation procedure is to fit the thruster drive unit and then install the propeller blades. This is followed by rigorous performance testing.
By using three special tools – a dome, a sledge and a hydraulic cylinder jack – a complete thruster with fitted propeller blades can now be exchanged on a floating vessel in around 12 hours. Commissioning is straightforward as the thruster is already fully assembled and shop tested.
A key element is the sledge that supports the thruster at a predetermined angle and enables a fully assembled unit to be slid out and back into the tunnel with minimal diver intervention, even in waters where visibility is poor. The dome, which has windows allowing the extraction and installation processes to be closely monitored, mounts on the tunnel and has an integral hydraulic jack to position and lower/raise the thruster and sledge. External services are reportedly limited to a simple crane on the dockside or pontoon; alternatively, a suitable lifting device on the ship can be used.
A trial project saw a Rolls-Royce TT tunnel thruster with a propeller diameter of 2.4m replaced on the ropax ferry Skåne with an exchange unit in under 12 hours: around half the time normally taken by a repair shop. All the ferry’s tunnel thrusters are now designed for skid-mounted removal and installation.
Other underwater repair techniques will be launched, says Ole Jacob Irgens, enabling vessels to remain on station while the work is done and reducing off hire time. As the OEM, Rolls-Royce manages and warrants the work.
Kamome Propeller of Japan manufactures two types of tunnel thruster. The TFA-type incorporates fixed pitch propellers and is available in a range of models with power ratings from 20-550kW. With a simple and robust structure, this product is designed to offer a high level of durability and easy maintenance.
If you want to learn more, please visit our website Underwater thruster manufacturer.