namniart

Feb 25, 2012 - Robot Progress

I’ve made a lot of incremental progress on my robot over the past few months. A lot of it deserves its own blog post; I’ll try to summarize things here, and then follow up with more detailed posts as appropriate.

First: the robot has a name: Dagny. Well, its had a name for a while, but it’s finally on the robot:

TODO: picture of one of the front fenders.

On the software side of things, I’ve significantly improved my integration with ROS. Where I was previously only using ROS as a message-passing architecture, I’m now working on integrating properly with the ROS navigation stack by publishing and subscribing to the appropriate topics as discussed in the navigation tutotials (TODO: link).

I’ve also written a proper URDF (TODO: link) for my robot, which means that I can effectively transform all of my sensor data into the frame of the robot for free, and I also get much better sensor visualization tools with very little extra work. Now I can visualize all of my sensor data with rviz! (TODO: link)

(TODO: screencap of rviz)

I’ve made a lot of progress on the firmware as well. Architecturally, I’m doing more processing on the arduino, such as GPS parsing and odometry calculations. reviously, I was passing raw NMEA strings up to the main processor, which were sent over a named pipe to gpsd and then returned as ROS messages via the gpsd_client node._ With the GPS parsing on the arduino, the system has fewer steps, isn’t as brittle as coordinating a system daemon with ROS, and there’s less data travelling over my serial link.

I also finally have my sonar sensors running again, and I’m publishing sonar data as ROS messages.

I spent some time dabbling with using rosserial (TODO: link) for my serial protocol, but all of the hacks that I had to do to get rosserial to run on top of my custom firmware resulted in a system that would only run for 10-15 minutes before crashing for reasons that I still don’t understand. The experience of running rosserial did teach help me come up with a better firmware architecture, and I found a couple of long-standing bugs in my libraries along the way.

With all of the software improvements, I’ve upgraded my sensor suite as well. I’ve upgraded my GPS to Sparkfun’s latest Venus GPS (TODO: link), and I’ve upgraded my 2-axis compass to a 9-axis IMU from Sparkfun (TODO: link), which includes a 3-axis gyroscope, 3-axis accelerometer and a 3-axis magnetometer.

(TODO: picture; new sensor suite)

And to support all of the new software and running the ROS navigation stack on my robot, I’ve upgraded the main processor from my old 500MHz Geode to a Pandaboard. (TODO: link). It’s a dual-core 1GHz ARM processor with 1GB of memory. The extra processing power and memory makes it much easier to run the navigation stack, and I think I still have some extra CPU power left over to do other inetresting things.

The next things to do are: * Restore the android in the firmware, so that I can get my safety lockouts and RC control back * Update the IMU drivers so that the axes are aligned properly with the robot * Update the IMU drivers so that the gyro, compass and accelerometer are scaled properly. * Use the accelerometer to tilt-compensate the compass * Write a sensor filtering/fusion algorithm to combine the odometry and IMU data into a more accurate position estimate

Once I have all of these basics working, I’ll be focusing on high-level code to allow me to compete in RoboMagellan at RoboGames (TODO: link), and the Sparkfun AVC (TODO: link)

Upcoming posts may cover: (this is my idea backlog at this point) * Using the ROS navigation stack on an ackermann-style robot * Using sonar sensors with the ROS navigation stack * Tilt-compensated compasses and sensor fusion * Experiences with rosserial * Expereinces with ROS on the Pandaboard * Outdoor navigation with ROS

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