More Feedback from the Field (Trident Kickstarter Update #29)

Original post: March 8, 2018

Hello everyone,

What’s in this update:

  1. Beta feedback and results
  2. Warranty information
  3. Cool videos we’ve received from community members in the field

First of all, many thanks to those of you who have been participating in our beta program and have provided thorough feedback. We’re really enthusiastic about how well Trident has been performing. Our beta pilots have been instrumental in showing us how we can make Trident better as they spend long periods of time in the field in a wide variety of conditions. I am extremely excited to share some of the incredible things beta users have done with their Tridents, but first I’d like to talk about what we learned we can improve.

TLDR; Following comprehensive beta testing, we have determined that the existing system works well in most saltwater and freshwater conditions, but testing revealed that in certain silty environments our motors can wear and rust in a way that we weren’t satisfied with. We found a way to make our motors more robust against silt abrasion and are upgrading the motors accordingly. Many customers will receive these upgraded motors automatically, but those early in the delivery queue are scheduled to ship with the original motors. If you’re part of this group (we will reach out to you directly if you are in this category) you will have the option to either receive your Trident as-is with first generation motors, or wait for the new version.

[If you’ve already received your robot, don’t worry. The motors are replaceable and are covered under our warranty which you can read more about below.]

Building the ultimate underwater motor

We began using brushless motors for our OpenROV kits back in 2012 and popularized the idea of using this type of technology for underwater applications. Since then, many others in the industry have adopted this approach, and we’ve spent a lot of time perfecting the concept. As you’ve seen in previous updates, everything in our thruster design—from our specially designed propellers to our field-oriented electric speed controllers—has been custom made for Trident. The brushless motors are no exception: we’ve designed them from the ground up for our application.

Trident’s motors are constructed much like the brushless motors you might find on a quadcopter. A series of electromagnetic coils on the inside “core” of the motor causes magnets on a rotating outer “bell” to spin based on the sequence of how each coil is energized. The one thing that makes underwater thrusters different is that they’ve been adapted to be extra resistant to electrical shorting in water and have no exposed materials that can rust. We spent many months designing these motors, and many of our prototypes were run for over 400 hours of testing in seawater to ensure they would work well throughout the lifetime of the vehicle.

Despite positive results during internal testing, after beta users spent more time in rigorous field conditions, we got some reports of rust accumulating in parts of the motor bell. It turns out that this was the result of abrasive particles making their way into the motor after piloting in heavy silt, causing the coating that protects the motor’s permanent magnets to wear. If this protective layer is worn off and the raw neodymium magnet is exposed to water - particularly sea water - rust can form from the magnet and eventually rub against the core of the motor. In some cases, this rust affected motor functionality. During beta testing we also learned that the outer part of the motor bell would sometimes lightly rust in a way didn't affect performance but was aesthetically undesirable.

While we believe the original motors we’ve designed will work fine in most conditions, we are striving to create a system that is robust in every condition. The reality of flying ROVs is that even experienced pilots often find themselves hitting the bottom and stirring up silt, and we don't want that to be something people have to worry about.

The New Motors

I want to share some of the steps we’re taking to perfect the design of the v2 motors to make them extremely abrasion-resistant.

Recreating the effect

Before addressing a design challenge, it is crucial to understand exactly what is happening in the system. To observe and measure the motor rust (and how effective our improvements are), we set up a test tank with exceptionally high silt content and ran a Trident in it to recreate what we had seen in the field.

Sure enough, running the motors aggressively in this environment caused the coating on the magnets to wear off, as well as caused some wear on the outside anodized portion of the motor bell.

OpenROV Trident

Gen1 motors after progressively harsh silt abrasion testing

Improving the magnet coating

Neodymium magnets designed for corrosive environments such as salt water are often coated with a series of plated layers consisting of nickel (directly against the neodymium), copper (on top of the nickel) and epoxy (which forms the outer layer of coating). Although this Ni-Cu-BE coating has great corrosion resistance, it actually does quite poorly with abrasion. For our motors, we chose a less common coating of “raw” epoxy which is corrosion-resistant and also better at withstanding abrasion than most other coatings. Our raw epoxy coated magnets survived testing in fresh, salty, and slightly silty/salty water, but as we observed in beta testing, they could not reliably withstand environments with very high silt content. We are now working with a company in the US that has special experience making extremely ruggedized magnets and has formulated an exotic coating for the neodymium which should be able to withstand the kind of abrasion our motors may encounter.

Widening the air gap

The area between the motor core and the motor bell is called the “air gap.” In traditional brushless motor design, this dimension is generally made as small as possible in order to get maximum efficiency from the motor. In the case of underwater motors that operate in dirty environments, however, it is important for the air gap to leave enough space to ensure small particles don’t get jammed between the bell and the core. We have suspicions that even with a large air gap, abrasion from very fine free-floating particles may still occur, but we want to make improvements wherever possible. We are currently deciding how to balance the trade off between resilience from a larger air gap and efficiency from a smaller one.

Improving the bell material

The motor bell is made from a cylindrical piece of metal with magnets attached to the inside circumference. The outer cylinder of the bell is more than just a mechanical housing as it actually plays an important role in directing the magnetic fields from the magnets properly. The outer part of the bell should have high magnetic permeability (that basically relates to how much iron is in it) in order to work properly. Most brushless motors, including our original design, are built using a type of carbon steel with high magnetic permeability that is plated with nickel or chrome to protect from corrosion. Although the effect was mostly cosmetic, we found that this plating, especially along the rim of the bell, would sometimes wear off and cause rust. To improve this behavior in our next generation of motors, we are validating a special type of high-magnetic-permeability stainless steel that can be constructed without traditional plating.

Every step of of this project has given us insight into how to how to make the perfect underwater drone. Many of the technologies used in Trident, from our injection molded pressure-proof enclosure, to our tether connector, to the way we communicate through a very thin tether, to the ruggedized design of our thrusters, had to be developed from the ground up. Making a product as ambitious as Trident requires innovation, and innovation often requires iteration. We appreciate so many people encouraging us as we’ve taken the extra steps necessary to make sure that the Trident technology and performance will be exemplary.

Premium Warranty

Quality is our highest priority from an engineering and design standpoint, as well as in the way we handle support. This is a good time to tell you about the warranty for Trident. We’ll have a separate update with all the specifics, but the important thing to note here is that we’ll be providing a premium warranty to all current pre-order customers. This means that if anything happens to the motors in the first year, we will swap them out for you. We want you to be proud of your Trident and confident that we’re standing behind our craftsmanship.

On that note, here are some of the amazing things that have been done with Tridents so far:

OpenROV Trident

The Triton Submarines team is planning to send Trident’s control signal through the acrylic pressure hull of their manned submersible - like a selfie stick for the sub! We can’t wait to see the results.

This species, known as a ratfish, was encountered during a dive with Trident beta unit, Rhemium, in the Puget Sound.

Footage of silky sharks in the Galapagos - captured by a Trident beta unit!

Glimpsing a pair of angelfish while doing a fishery survey off Grand Cayman.

This quarry outside of Charlotte is home to endangered paddlefish. They didn’t seem to mind Trident at all!

We couldn’t have made it through this process without you! We’re excited to follow along with your Trident expeditions, too. Please reach out to support@openrov.com with any questions, and thanks as always for joining us on this adventure!