2013 Posts

Now that you know what the IGVC is about, I'll go into some detail about our high-level approach. The challenge provides some obvious requirements:

• A reference frame relative to earth to navigate to waypoints; GPS provides position and compass provides heading
• Line detection to stay within lanes; a color camera suffices
• Obstacle detection; a 2D rangefinder is the is logical choice
• Precise measurement of velocity; provided by encoders, accelerometers, and gyros

I'll go through each requirement in a bit of depth, describe typical solutions, and design constraints. 

An absolute reference tells the robot exactly where in the world it is. GPS and compass provide that data. Unfortunately, GPS is only accurate to about 6', so it isn't useful for local navigation. A 2' difference in position is the difference in hitting an obstacle and avoiding it. The GPS is useful for providing long-range direction: the goal is 60' southwest.

Most teams improve their GPS accuracy with exotic antennas and exact correction services (the speed of light varies through the atmosphere, distorting timestamps and GPS location. A corrective signal provides the difference in true and measured time-of-flight, improving accuracy.) Although these units offer remarkable resolution (within 6"), they are prohibitively expensive ($20,000). 

Lafayette's team, named Team Terminus, will use an inexpensive GPS receiver, accurate to roughly 6'. It costs less than $100. (Cost, by the way, will be a persistent theme. Most IGVC robots run $20,000 to $80,000; Lafayette budgeted Terminus $6000.)

Yesterday, I went for a walk. Getting outside is always relaxing, and the town was beautiful in the dark, decked out for Christmas.

I also saw a broken electric radiator curbside. At least I hoped it was broken. On the way back home, I found the house again, hefted the thing onto my shoulder, and carried it a mile home. (I set it down too hard when I arrived and broke two of the casters. Now it was definitely broken.)

Hopeful, I plugged it into the wall, turned it on, and... nothing! Hooray! I had an excuse to take it apart. (The heater, by the way, is supposed to retail for $80. It's also got bad reviews, but hey. Free.)

For a few glorious hours, my dining room was transformed into a wood shop. 

Okay. "Glorious" is an exaggeration. So is "transformed" and "wood shop".

For the past month, I've been organizing an international food tasting entitled "Technology of Food". International students are presenting food from their homes, with a focus on how the resources and history of the nation shaped its cuisine. 

"Pannier" means two things. A pannier is either the thing that women wore in the 18th century to make their dresses all floofey or it's a type of luggage carried on the side of a vehicle or beast of burden. Needless to say, I'm working with the second sort. 

A while ago - say, two years, I got a rack for my bicycle. The rack included a pannier, which was terrifically exciting. It had a center compartment where I took to carrying some basic tools and a reflective vest, and two zipper side pockets that could hold a fair volume. It was great, being able to take my bike grocery shopping or to use the side bags to carry books. 

Like all cheap things, though, the bag broke. The side pouches were made from nylon and the seams just pulled right out. Ditto for the center bag - the floor and walls had an argument (or something) and came detached from each other. 

Yesterday, I passed a 1 yard remnant (that means cheap) of duck canvas in a craft store. I'd been looking to make myself a set of bags for a while, and this seemed just the chance. (Plus, it was black. I love black.)

Today, I started making the thing. I passed up a few designs for being too bulky or too simple, then found a nice one at bit-of-green.com. The design was simple but usable, light but durable, and easy to modify to taste. Plus, the author included readable set of plans.