Around the Americas

Friday, September 25, 2009

The folks on the Around the Americas cruise stopped by to build some sea perch and get a demo of our REx II vehicle.

Power Supply Crate

Monday, September 14, 2009

One of the annoyances of transporting our support gear has been finding ways to carry and stack the power supply that we use to recharge Odyssey IV's battery. The charging cable is 50 feet or so and 1" in diameter -- a bit difficult to wrap your hands around when it's all coiled up. The power supply itself is large and flat with protruding pieces on all sides (rackmount ears, knobs, and terminals).

To kill 2 birds with one stone, I made a crate that uses the power supply for its bottom.

One of the constraints I put on this project was to be able to get the power supply out without using tools. So, I made some notches for the ears to fit into instead of using the rack-mounting holes. This keeps the power supply from sliding around and also keeps a gap around the edge so that air can get into its vents.

The front part was a bit more interesting. I had to be able to access the knobs as well as leave enough room to lift the power supply out of the notches. On the other hand, I had to prevent the cable from spilling out. The solution was to have a large wooden latch that would rest on top of the supply to retain the cable but could be flipped up to remove the power supply.

Visual Servoing at UNH, Day 3: Style points

Friday, September 11, 2009

I had written a new web-based GUI for the vehicle's onboard database, with some open flash chart graphing capabilities. When we recorded the overnight recharging of the Odyssey IV battery, my code got its chance to shine.

As you can see, cell 10 seems to be defective and it will probably be replaced soon.

Since we were able to closed-loop control our position and yaw based on the camera, and our altitude based on the DVL, it made sense to close the loop on sway based on our heading.

This means that we can say "look at the south side of the pipe", and it maintains a position on the south side of the pipe. In this nav plot, we visited the east, south, west, and north sides.

We packed up and headed back to the lab. Another very successful trip!

Visual Servoing at UNH, Day 2

Thursday, September 10, 2009

The day started off very well, with us checking out the mounting pole for a piece of multibeam sonar equipment that was being tested earlier in the week.

Satisfied that the image processing component was working properly, we switched to the 13cm pipe that we would be using for our demo.

Almost immediately, we ran into trouble... all of our calculations for distance were off. We ran and re-ran our calculations for the angular resolution of the camera, and for calculating our distance from the pipe based on its width in pixels on the video.

An hour or 2 later, we noticed that we had accidentally declared our angular resolution as a boolean instead of a double. That's a pretty big error! Surprisingly, it only affected our distance calculation by a factor of ten. But once we fixed it, we were spot on.

The results are dramatic!

Visual Servoing at UNH, Day 1

Wednesday, September 9, 2009

Today we are at UNH to work on some visual servoing code that Justin wrote. The goal is to be able to follow a vertical pipe, controlling yaw and position based on image processing.

Mike has mounted the camera on the bottom of Odyssey, facing forward so that we will be able to track an object in front of the vehicle.

Early on, we had to re-adjust the aperature on the camera. We had made it as small as possible to increase our depth of field, but it was just too dark in the facility to see anything on that setting. So, we opened up the aperature and double checked the focus.

With the vehicle on an ethernet tether, we were able to use coriander to tweak the settings of the camera once it was underwater. This program makes the tuning stage go very quickly!

REx II is Back in Cambridge

Thursday, September 3, 2009

Today, we got the REx II vehicle back from Hawaii.

Due to restrictions on shipping, we didn't bother to send the lithium ion battery by mail. Instead, we just built a new one.

Unlike the battery for Odyssey IV, this battery is designed to fit into the bottom half of a pressure tube. The individual supercells are not wrapped in plastic, but instead squished together to form the full battery.

The electronics fit on top.

Potting: A Mini-Howto

Tuesday, September 1, 2009

I put a mini-howto on potting on our wiki.