I’m going through a rough period right now. There’s an illness in my family and I’m having a hard time focusing on anything but worrying and trying to take care of health stuff. Everyone is going to be okay, but it’s going to be a difficult four or five months, and I really appreciate your patience and understanding. I’m going to keep putting up comics, but I don’t how much else I’ll be able to work on.

To anyone I’ve been corresponding with, I’m sorry that I may be even more tardy than usual. While davean (the xkcd sysadmin/business manager) monitors the address, I know he only forwards to me a fraction of the huge flood of mail that goes there. If you’re trying to reach me personally about something, you can write to me directly at, but I’m afraid I won’t able to reply to most of it right now.

I know there haven’t been any posts here in a while. Since most of my projects are on hold right now, I thought I’d share some pictures from one that’s almost done: an underwater ROV. Exploring lakes and oceans has always fascinated me, and while I’ve spent a lot of time snorkeling and free diving, in the end I’m more interested in sending robots than going myself.

I tried to build a couple of ROVs in high school out of scavenged R/C cars and spare parts, but none of them ever worked very well. Last summer, I got interested again and picked up an Inventivity ROV-in-a-Box:

Inventivity ROVIAB

It’s a very basic kit designed to use off-the-shelf parts as much as possible, to encourage people to play with the design or expand on it. I’ve gotten a lot of help and some cool ideas from the company founder, Dr. Karen Suhm, who coaches robotics teams in ROV-building competitions and generally knows everything about ROVs. The kit comes with a good set of underwater motors and a sensitive camera, and this summer I started modifying it to use an Arduino and joystick control, running the whole thing over Cat-5 cable (which significantly lightened the tether). This will also let me add other equipment, like a still camera, depth gauge, compass, and sonar.

It’s very close to being finished—I just have a couple wires to reroute and a leak to seal—but for now, here are some pictures from construction and testing:


I made a coupler so the tether could be detached, and added a chamber to hold the Arduino, Ethernet shield, and motor control board. A Python script on the surface translates joystick values into motor speeds, and the Arduino has some code to listen to commands via the Ethernet and control the motors using three TLE-5206 H-bridges. The 5206s offer more protection than some other H-bridges—I initially used some smaller chips, and managed to blow out a couple. (Thank you to mpanetta of #sparkfun for hooking me up with the 5206s.)

A note to anyone who wants to build something like this: the Arduino isn’t actually capable of processing video, so you’ll need to either put an Ethernet camera and hub on the rover, or—if your camera isn’t digital—do what I did and divert two of the Cat-5’s twisted pairs to carry RCA video, running the Ethernet solely on the other half.

This canoe (and everything else in the shot) travels through time.

My friend Mike loaned his canoe for depth testing in Walden Pond, which is (according to data from the 1940s) the deepest lake in Massachusetts

It's about 90 feet down from here.

At the bottom of Walden, there are close to three extra atmospheres of pressure.

In this shot, read left to right.

The zip ties double as binary depth markers. This one is 14 meters.


This is the vacuum pump for sealing up wires passing into the sub (it’s sitting atop a draft of the online communities map). If you open up the exterior/water side of a cable and submerse it in a pool of marine epoxy, then apply suction to the dry interior of the sub, it sucks the epoxy through the cable, plugging it up completely. You can also use it to suck all the air out of a wine bottle with random objects inside. It’s fun to see how different materials react to a near-vacuum—particularly if you’ve just drunk a bottle of wine. I didn’t get much more done that day.

Lastly, here’s a clip of the bottom of Walden Pond, about 80 feet below the surface.  This was an unpowered pressure test—the sub was just dangling on a rope—so it’s not very exciting, but it was the only test where I could record the video feed:

The Walden lakebed is pretty dead—the material you’re seeing is flakes of debris stirred up by the sub. In other lakes, we’ve found cooler stuff.  In Seymour Pond on Cape Cod, we had huge catfish fish swim up to the camera and look at it, and we explored a sunken fishing boat on the bottom of Sheep Pond.  I’ve also learned that deck chairs apparently fall off docks all the time—the lakebed 20 feet below the dock on one lake was absolutely littered with them.  When I get a chance to send it to some more interesting places, I’ll be sure to share footage.

P.S. A belated thank-you to the NYC Makerbotters; after I posted comic #743, they fabricated and mailed to me an actual tiny open-source violin.

664 replies on “Submarines”

  1. Marshmallows in a vacuum=way entertaining.

    Also, I wish you and your family well. I’ve been there, and you should take all the time you can to hang out and talk with your family, play games, and get drunk. Hope it gets better for you. x


  2. I fucking love you for the #841

    Anyway. I hope all the best for you and your family.



  3. Why use ethernet? why not run USB over the ethernet cable and not have to deal with the shield. and you could run 2 (or more if you had a common power and ground) USB connection through it, allowing you to use a USB webcam!


  4. I was so sorry to hear what you were going through since November….and seeing your Monday April 4 comic – I wonder if things are better or how you’re coping up with the illness in your family. Your comic strip has made so many, many of us laugh through the years and have a sense of humor about life through our tough times, wishing you strength during yours.


  5. Does anyone know about how much coding one would have to be able to do to work that particular robot? also, how modifiable is that kit exactly? I can think of some cool design mods, but i have never written code before, and i dont want to get excited about something that will put me in way over my head…


  6. /’/…/…./…../ˉ
    ……..(‘(…′…′….ˉ~ /’)

    Google in the input: = ==you can find many brand names, even more surprising is that he will sell you the unexpected o(∩_∩)o



  7. I love your ethernet-wired sub. You should add a live feed so you can give your catfish admirer a live video blog lol

    What did you use for materials for this sub?


  8. Sie amk. I was so sorry to hear what you were going through since November….and seeing your Monday April 4 comic – I wonder if things are better or how you’re coping up with the illness in your family. Your comic strip has made so many, many of us laugh through the years and have a sense of humor about life through our tough times, wishing you strength during yours. vay ak.


  9. Close this comic down Randall, it sucks these days- you aren’t fooling anyone anymore. I bet your girlfriend looks like a pizza that has been sat on.


  10. Great Work

    Interested in your coupling for removing the tether- pvc pipe fittings? Any chance you can elaborate on its construction?



  11. Here’s a quick EXAMPLE of Non-Native FISH in WALDEN POND that someone (without a ROBOT SUB) photographed in WALDEN POND.

    please see:

    Walden Pond Koi
    TheGizzard49 TheGizzard49·4 videos
    Uploaded on May 19, 2010
    Walden Pond Bass Fishing and Kayaking with Hobie Adventure Island and Sanyo Xacti CA9 waterproof camera

    p.s. He used a SPECIAL Hobie Kayak.


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