Hello Reader,

Welcome back to The Build Log! Today, we can finally share our process of testing our autonomous submarine last week!

As you might know, we're finally developing our autonomous submarine to be able to navigate underwater by itself. This is very difficult for a couple of reasons. The main reasons are:

1. There is no GPS underwater - we need to rely on an advanced DVL (doppler velocity log) sensor for navigation & compass.
2. There is no way to communicate with our submarine while underwater - if the submarine gets lost underwater, it will be very difficult to find it again.

There are multiple things that can go wrong in this kind of system - like for example an inaccurate/failing DVL, a failing compass, a failing program etc. So, for the initial testing, we decided to swim with a small visual marker attached to the submarine via a piece of string. This allowed to us keep an eye on it, as long is stayed relatively close to the water surface (the depth we used for the initial tests was only 0.5m). We removed it later.

The DVL is actually quite a simple sensor to use - it returns the current velocity of the vehicle relative to the sea bottom, and the compass, which is built in to the antenna mast of the drone is providing us with the current orientation of the submarine in space. Combining these two data points, we can make an educated guess on where the drone is (this kind of navigation is called dead reckoning).

The drone is first supposed to get a position lock at the surface with the GPS, and then, once it submerges, switch to dead reckoning mode. The first time we tried it, the submarine unfortunately crashed into the bushes of the lake we were testing on:

We redid the test a couple of times and every time, the dead reckoning was failing in the same spot - the submarine was just going into the bushes, and not recovering. We were stuck at this problem for a couple of days - trying to do simulations and trying to find a bug in the code (which we couldn't find). We're going to share the reason for why this has happened and what we did to fix it in the next release of the Build Log, so stay tuned!

If you want to build an underwater project, the easiest way to get involved is to build the entire CPS 3 drone with our DIY Kit -> now available!

You don't have to buy any components separately, because they're all in the one box delivered to you.

Cheers,

Piotrek, CPSdrone

PS: You can access all of the previous releases of the newsletter here.

PS 2: A big thank you to everyone who has replied to our poll about the next version of the CPS 5 - we definitely learn a lot from your feedback, and will give you a product you actually want to see. Thanks!