SeaCharger build blog: see the latest progress on the project

Autopilot!!!

2/2/2016

The cool thing about a project like this is that it encompasses so many different disciplines. I'm mainly a mechanical guy, but I'm getting to learn a lot about autopilots and navigation and Arduino.

Here you see the beginnings of Seacharger's autopilot. Clockwise from the upper left: tilt-compensated compass (Devantech CMPS-11), Seeeduino Mega (basically an Arduino Mega in a slightly smaller form factor), servo mux board from Pololu, R/C receiver, Adafruit GPS, and a servo. Special thanks to JT for putting together all these components and getting them to talk to each other!

After reading about Arduino code and making a mockup of the autopilot in Excel, I managed to get a pretty decent autopilot working. What I mean by this is that I could program in some waypoints and then take this setup to a local park and have it guide me to the waypoints by moving the servo arm in the direction it wanted me to walk. There were a lot of bugs in the code, mainly having to do with passing from 359 degrees heading to 0 degrees heading or from 180 degrees to -180 degrees. But I got all those worked out and it's all good now. This kind of work is really fun because you can make progress so quickly. Those software guys have it easy!

6 Comments

foxbravo

2/8/2016 10:53:42 pm

Hi there,
very interesting project, nice work so far. Your site got my
attention a long time ago, but I wonder why you do not use an off the shelf autopilot. So many guys have made so many experience with stuff like that. Why don't you make use of it?
Actually there is even a user group for autonomous boats at diydrones:
http://diydrones.com/group/arduboat-user-group
I'm owning and using two ardupilots by myself and can really recommend it.
Keep up the good work!

Damon

2/9/2016 08:17:36 am

Hi foxbravo,

Thanks for your question! This is actually something we thought about a lot, and who knows whether we made the right decision or not. But the main reason is that the available autopilots seem to have A LOT of functionality that we don't need (such as all the stuff you'd need to fly an airplane, or all the stuff you need to create a pretty GUI) yet are missing some functionality that we do need (such as being able to automatically reduce power to the motor based on battery voltage). We knew we'd have to have a separate microcontroller to do those functions anyway, so having the microcontroller plus off-the-shelf autopilot seemed redundant. It's actually easier for to write your own autopilot code, which is in our case is probably no more than 50 lines of code, than to go through thousands upon thousands of lines of somebody else's code trying to make it work for your own application. Of course the risk is that there's a gotcha in there somewhere that somebody else has already fixed but that you don't foresee. We'll just have to see how it turns out!

Having said all that, we did copy as much as possible from other people, such as the equations for bearing from point A to point B on the globe and for cross-track error and many other equations. The actual navigation algorithm is ours, though.

Damon

Stu

9/19/2016 12:10:50 am

Hi Damon will you be releasing the code and build diagram so others can build their own boats? I'd be interested in putting one together

9/20/2016 12:52:48 pm

Hi Stu,

My day job is engineering for Liquid Robotics, where I work on autonomous boats. We are interested in exploring development of a solar-powered vehicle similar to Seacharger, so it wouldn't be appropriate for me to release the detailed technical details, beyond what I've shown in this build blog. Sorry!

sameer

4/8/2017 06:05:41 am

which electronic speed control was used in this project ?

4/10/2017 06:45:59 am

Hi Sameer, it was a Castle Creations Phoenix 25. One that I've had for years and years, so kudos to them for reliability.

Autopilot!!!

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