Tecnadyne: Propulsion Systems For AUVs

More than 30 years ago, Tecnadyne delivered its first thrusters to Mitsui Engineering and Shipbuilding in Tokyo. Since then, the company has manufactured and delivered over 8,000 thrusters. The primary focus of the company has been underwater propulsion, motion control, and related technologies for remotely operated vehicles (ROV). Headquartered in San Diego, California, Tecnadyne’s manufacturing facility is involved in design, fabrication, assembly, and development of customized subsea systems. The company more recently has increased its focus to include propulsion systems for for AUVs. ON&T talked with founder and president o f Tecnadyne, Andrew Bazeley.

ON&T: Could you give us some background on your AUV propulsion systems?

Bazeley: We have a fairly new application, which is building thrusters for AUVs. When I started the company 34 years ago, we were building thrusters for just ROVs. The thruster for an ROV is more of a general thing. You’re just concerned with how much push you can get out of that thruster—you really want the most bang for your buck. When you make a thruster for an ROV, it’s a more compact thing, it produces a lot of thrust but isn’t very efficient.

ON&T: Now you are designing thrusters for AUVs. How is that different?

Bazeley: Every single AUV is different in its requirements for the propulsion, and it is different in how they move through the water at a forward speed or velocity. Sometimes they move quite fast. They need a thruster or propulsion system that allows them to move through the water at the speed that they need to move. They also need to do so as efficiently as possible. It has to be efficient because, in almost all cases, a battery powers AUVs. In order to stay underwater to complete a mission, you are juggling the amount of power in the battery and the power of the thruster.

ON&T: So, you are dealing with a much different case in AUV thruster design.

Bazeley: Yes, a special or purpose analyzed and design thruster needs to be built for each AUV. We have to look at how much power that AUV can deliver, but we need to look at what speed it needs to move through the water and how much thrust it’s going to take to move that AUV through the water at that speed. We have developed some very good analytical tools to model appropriate propulsion. We can play with a lot of propeller characteristics. This isn’t something that is totally new and unique because modeling propellers for optimum efficiency has been going on in the shipping industry and the ship building industry since the beginning of propeller-driven cargo ships. In their case, they are crossing big oceans and want to do it as efficiently as possible. It is not that they have limited power on the ship, but they want to use as little as they can and as cheaply as they can to maximize their profits. The difference is that an AUV operates submerged, while surface cargo ships have to take into consideration the air/water interface.

We have developed some very good analytical tools that not only allow us to optimize the propeller design, but also optimize the propeller design working in concert with an electric motor and, in most cases, a gear box to reduce the speed from the electric motor for a proper speed for the propeller. We are now able to very accurately model the entire propulsion system for an AUV. We can analyze, design, manufacture, and deliver an AUV propulsion system that meets the performance and mission requirements of that particular AUV.

ON&T: Could you talk a little more about the tools used in your process?

Bazeley: The analytical tools we have are all software. The design of the thruster uses fairly well established hydrodynamic principles. The data have changed over time, but knowing how to use those data, information, and know how is another matter. Especially when applied to the AUV case, which is a little bit different from the established applications. We also have the ability to model the electric motor and gearbox with the propeller and are able to treat that entire propulsion system as a single black box. The client puts in power on one side, and we deliver propulsion or thrust on the output.

DC Brushless Thruster Model 560.

In addition to those analytical tools that we have which are all software based, we have pretty sophisticated testing abilities. We are able to test the performance of these propulsion systems and thrusters that we build. We are able to do that in a pretty timely and cost effective way. Part of the reason we are able to do that is because we rely on many of the building blocks we have designed over the 34 years that we built thrusters for ROVs. We are able to choose from a dozen motor frame sizes that we already have comprehensive performance data on and that we have in stock. We are also able to select from maybe 18 or 20 gearbox configurations that we have already built and tested and generated the performance data. We have the ability to take these different components off the shelf, and that is what we do when we are doing the analytical work. We are just using those building blocks that we have and have developed over 34 years. We have them all on the shelf.

ON&T: So, you are creating new designs for AUV applications built on time-tested components.

Bazeley: Yes, we are able to marry that to new propeller designs so that we can do rapid prototyping. Depending on the size and complexity of the propeller we will, at least at the prototype level, print the propeller in 3D or an investment cast of the propeller out of stainless steel.

ON&T: You’re also providing the client with a one stop- shop experience.

Bazeley: Because of our experience and vast array of building blocks, we are able to build the entire propulsion system in one black box assembly. It is not a matter of a customer going to a company to design a propeller for them and then going to another company for the motor and then another company to bring the two together and then realizing for one reason or another the performance doesn’t meet the needs for the propeller. That happens a lot, believe it or not. We are able to conceptualize, design, develop, and manufacture these propulsion systems and get them in the customers hands in a relatively finite and reasonable amount of time with a pretty high degree of confidence that the performance they see when they get that thruster is the performance they were anticipating.