Sunday, February 23, 2014

It's actually alive!

Over a year ago, I posted about my RoboMagellan robot, and then nothing. It's been pretty busy for the past year, but I finally got back to working on this robot. The control board is now mostly functional, and I have integrated the IMU and GPS. I still have to get the tilting laser assembly mounted and working, and come up with a permanent mount for the camera, but earlier today I finally field tested the robot:

Drives well in grass, on pavement, and even has enough gusto to get up onto concrete parking lot wheel stops (although it tends to then get stuck on top of said stop). The forward odometry is good, but I still need to tune the turning odometry.

As far as ROS integration goes, I have the IMU, GPS, and wheels tied into ROS. For decoding the GPS I'm using the nmea_navsat_driver package, which made things quite easy. I'm currently working on some tools for handling localization and visualization while in a GPS coordinate frame (more to come on that, but it is developed on top of geodesy). Code for the project is pretty minimal right now, but is hosted at

Sunday, September 29, 2013


It has been a while since posting, I figured I'd give an update on a project I've been working on recently: a ROS buildfarm using BuildBot.

Of course you are probably thinking, "but ROS already has a buildfarm?" And that is correct, however I found that it was quite hard to setup a personal instance of the Jenkins-based farm that builds ROS Debian packages. There is not all that much documentation, and extending it is not ideal for me as it uses an interesting mix of java-ish stuff.

Enter buildbot. Buildbot is like Jenkins, except completely written in Python, and I like Python. While buildbot doesn't have as many features and plugins as Jenkins, it has more than enough to get the job done. Anyways, I created a buildfarm  using buildbot + catkin, which can do the following:

  • Build Debians, just like on the ROS buildfarm. This includes doing it all in a cowbuilder so you know that the dependencies are right.
  • Build test jobs, similarly to the ROS buildfarm, whenever you push to a repository (only git is supported)
  • Build doc jobs, pretty much like the ROS buildfarm.
  • Build arbitrary source debs into binaries.
The system loads its configuration from a rosdistro file. In addition to loading what to build, I also have it setup to load where to get debs from in the rosdistro, making it easy to change deployment setup.

Buildbot-ROS is still quite early in development, but does most of the things that an individual or small team would need internally. The documentation is in the README, which gets nicely rendered by github. The code can be found on my github account:

Tuesday, May 21, 2013

Generating an IKFast Plugin for MoveIt

Over the past few weeks I've been using MoveIt quite a bit -- I was actually using the Pick and Place actions for Maxwell's chess playing last weekend at Maker Faire (an updated on that shortly).

I recently changed over to using IKFast for IK under MoveIt. This fixes a number of problems with the default IK plugin. I'm using ROS Groovy under Ubuntu Precise, and ran into several issues which I thought I would mention here.

First off, I start with the excellent moveit_ikfast_generator from Dave Coleman. You should run his instructions for "Create Collada File for Use with OpenRave". Once you have a collada file, here is what I did to make the ikfast generator work:

      sudo apt-add-repository ppa:openrave/release
      sudo apt-get update
      sudo apt-get install openrave0.8-dp-ikfast

At this point, I had to edit a /usr/lib/python2.7/dist-packages/openravepy/ to add the following line just after the copyright:

      __openravepy_version__ = "0.8"

Without this, nothing seems to run. Once the code is updated, the tools listed in section 5 of the ROS Industrial tutorial work as indicated.

Then it's back to the README in moveit_ikfast_generator, where the instructions will walk you through generating the ikfast plugin. One note there is also a command for: my_robot.dae --info joints

which is very helpful if you have a 7-dof actuator and need to fill in the --freeindex parameter.

I'd like to take one quick moment to thank Dave and the ROS Industrial team for their documentation, and Ioan Sucan and the rest of the MoveIt team for the great platform they've provided.

Tuesday, April 30, 2013

Blast from the Past: PR-MINI

I was recently updating my personal website when I realized that I had some projects that had never seen the light of day. This post is about one of these old projects that I never showed off:

Back in late summer of 2010 I started to build a miniature PR2. It was a 60% scale model of the PR2 arms, base, and torso. The base was differential drive instead of the more expensive casters found in the PR2. I reused the motors and 6" wheels that had previously been used in REX, one of my first large robots. For this robot, the frame was primarily 8020 Aluminum rail covered/connected with laser-cut ABS and the occasional sheet metal bracket:

The head sported a pan/tilt, which used two AX-12s for tilting and a third for pan. It had two webcams for stereo, and was designed with enough space between the web cams to install a Videre short-range stereo camera, although I never got around to that:

The arms were pretty massive, nearly 0.6 meters long, with 7 servos. The shoulder pan, forearm roll, wrist pitch and wrist roll joints were AX-12s. The shoulder lift joint was an RX-64, while the elbow and upper arm roll joints were powered by (admittedly, under-powered) RX-24F servos:

The torso had a 12" throw linear actuator, and used expensive and heavy 8020 parts to form the bearings and rail:

The entire thing was controlled by a laptop, tucked into the base, and an ArbotiX prototype with integrated motor drivers. When dealing with robots this big and heavy, an E-stop is a must. The wiring on the back panel was made somewhat tidy, and covered with Lexan shells:

I went as far as moving arms around under ROS, and tuning in the navigation stack a bit. The code developed for this robot later became the arbotix_ros drivers:

A couple of things did this robot in. First off, it was really heavy (45lbs) and hard to easily transport around (which I was doing a lot of back then). Transport was quite funny as well, because the arms loved to dangle in every possible direction, leading to the "bubble-wrap straight jacket":

Second, the Kinect came out shortly afterwards, making the sensor suite pretty lacking, and looked ludicrous trying to strap a Kinect on this robot. A number of lessons learned are pretty clear in Maxwell, which was built shortly after this robot sacrificed his arms. Oh, and since I couldn't find a reason to slip this picture into the story above, here is a view of the Autodesk Inventor CAD model:

Monday, April 29, 2013


PR-Shelf, the most awesome, not-actually ROS-powered, robot shelf:

Saturday, April 13, 2013

National Robotics Week: Robot Block Party Pictures

I wasn't at the Robot Block Party last year, but I was amazed this year at how much bigger it was. Two years ago, there were like all of 5 tables on the outside patio, this year there were like 20, and they were all full of robots. I didn't take any photos, but there is plenty of coverage elsewhere: HBRC member Tim Craig took a bunch of pictures. Camp Peavy, another HBRCer took some more pictures.

Updated 4/15: IEEE Spectrum also now has some coverage.

Monday, April 8, 2013

National Robotics Week (and a quick note on MakerFaire)

It's National Robotics Week! And apparently, there is just TOO MUCH ROBOTICS for just one standard week, because NRW spans 9 days, and the website lists events pretty much all month.

There are a number of events in the Bay Area. First up is the Robot Block Party at Stanford from 1-6PM on Wednesday -- there are usually a ton of bots around in a somewhat impromptu show and tell. While I don't think I'll be pulling Maxwell out for this event, I'll probably be there for the later part of the event. Oh, and it's FREE.

Also this week is an interesting event by on Thursday at SRI, put on by Xconomy: Robots Remake the Workplace. Including a keynotes speech from Rodney Brooks.

April 19-21, it's RoboGames! Maxwell will be making an appearance there for sure, likely in the Silicon Valley HomeBrew Robotics Club booth.

And finally, Maxwell will battle PR-Lite at MakerFaire 2013. In chess, that is. That's right, I've dusted off the old AAAI Chess code and the PR-Lite guys have been working to adapt it to their robot. I actually ran into some major issues upgrading the chess code to Groovy as many of the PCL nodelets were not ported forward during the catkinization. So, I took this as an opportunity to rewrite the whole board/piece detection pipeline into a single node that is way faster than the old one, taking into account a number of better heuristics.

I'm still working to integrate MoveIt instead of arm_navigation, but the current code is posted now on github.