On track, working hard (Trident Kickstarter Update #19)

Original post : March 20, 2017

Hello everyone,

Things are going well at OpenROV and we expect to begin assembly of the first production Tridents toward the end of April. Our final design is complete and we are now zeroing in on our production plans for the many units we plan to ship this summer, starting with Kickstarter-backed units and moving on to pre-ordered vehicles. We plan to ramp up production rates over the first few months to ensure that the quality of our first vehicles off the line is satisfactory while proper assembly procedures are still being developed and tested.

Production capacity has been one of the most important topics we've been planning around. Our goal is to balance producing and shipping vehicles quickly without compromising quality. We’re working on the final details for production with our contract manufacturer, and are eagerly anticipating the full production schedule - we’ll share that with you as soon as we’re able.

We appreciate that so many of you have been waiting patiently while this information is gathered. As always, our aim is to communicate regularly about what we're learning and the decisions we're making based on that information.

Meanwhile, our software team has been working aggressively to optimize the user experience for Trident. We've made two major advances so far:

  1. We've begun development on a native app for mobile devices that optimizes mobile performance while flying the vehicle.

  2. We've designed our own motor control algorithm that will give Trident profoundly better control than any other ROV in its class.

We're quite excited about both of these developments, so I'd like to go into each of them in a bit more detail.

Native App

A cornerstone of our software architecture to date has been that our vehicles host a web server from onboard, so all that your computer needs to interact with the ROV is a web browser. This architecture is very extensible, but can be limiting when more advanced functionality is needed that web browsers don't yet support. Mobile devices such as smart phones and tablets have many capabilities that can be utilized more fully with a native app, so we decided to write one. While browser-based control will still work for Trident (and will be the primary way to use the vehicle from a laptop), our native app will provide enhanced mobile device performance for things such as video streaming, data storage capacity, and interaction with the device's on-board features such as physical buttons and internal sensors like GPS and accelerometers. To start out, this app will be for Android devices only, but we plan to extend it to iOS devices later on. We'll publish more about the OpenROV App once it is closer to completion.

Motor Controller

It may not seem obvious at first glance, but the electronics and computational logic needed to make a brushless motor spin are actually quite sophisticated. Brushless motors move by turning fixed electromagnetic coils on and off in the right sequence and timing to pull and push the rotating magnets around. In order to know when to turn these coils on and off (as well as which polarity they should have) the coils are also used to sense energy generated by the solid state magnets as they move past the coils - in the same way a generator produces electricity. The most basic process of sensing magnet position in this way is called "Back EMF" detection. Almost all hobby-grade brushless motor Electric Speed Controllers (ESC’s) use back EMF for control, but this method is somewhat inefficient and does not provide the fine-grain speed control that more advanced methods do.

For quadcopters and RC airplanes, simple control schemes like Back EMF are acceptable because motors in those situations don’t often require being able to operate well at slow speeds. In ROVs however, RPM has to be managed perfectly at high speed in strong currents as well as while moving slowly through extremely delicate environments. Without nerding out too much, one of the ways to get extremely good control of a motor is with a process called Field Oriented Control. This more advanced method of motor control senses current flow on each of the electromagnetic coils and drives the motor with a waveform that is optimized for the position of the magnets at any point in time. The result is greater efficiency, quieter operation, greater knowledge of the motor’s behavior, and controllability at all motor speeds. To demonstrate, we recorded this short video showing how slowly and quietly our motors can operate at low speeds, and how much power they can deliver at high speeds. We’re very proud to be putting such an advanced electronics and software package inside Trident, and we hope you’ll appreciate it too!

After what seems like an eternity of focusing on the details of Trident’s design, it’s incredible to finally have something in front of us that does what we planned. We recently loaned one of our Trident prototypes to renowned underwater photographer, Eric Cheng, for an expedition off the coast of Western Australia. While doing some field testing for us, Eric managed to get some great video clips. We’d like to share one we enjoyed with you:

We’re eager to get Trident into your hands, and we’re looking forward to hearing what you discover with it. Until then, please let us know if you have any questions, and stay tuned for a detailed production/shipping schedule in the next several weeks.