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• ROS In Three Dimensions: Navigation and Planning Will Be Hard

  Roger • 7 days ago • 0 comments

  At this point my research has led me to ROS modules RTAB-Map which will create a three dimensional representation of a robot's environment. It seems very promising... but building such a representation is only half the battle. How would a robot make good use of this data? My research has not yet uncovered applicable solutions.
  

  The easy thing to do is to fall back to two dimensions, which will allow the use of standard ROS navigation stack. The RTAB-Map ROS module appears to make the super easy, with the option to output a two dimension occupancy grid just like what navigation wants. It is a baseline for handling indoor environments, navigating from room to room and such.

  But where's the fun in that? I could already do that with a strictly two-dimensional Phoebe. Sawppy is a six wheel rover for handling rougher terrain and it would be far preferable to make Sawppy autonomous with ROS modules that can understand and navigate outdoor environments. But doing so successfully will require solving a lot of related problems that I don't have answers yet.

  We can see a few challenges in the picture of Sawppy in a back yard environment:

  • Grass is a rough surface that would be very noisy to robot sensors due to individual blades of grass. With its six wheel drivetrain, Sawppy can almost treat grassy terrain as flat ground. But not quite! There are hidden dangers - like sprinkler heads - which could hamper movement and should be considered in path planning.
  • In the lower right corner we can see transition from grass to flat red brick. This would show as a transition to robot sensors as well, but deciding whether that transition is important will need to be part of path planning. It even introduces a new consideration in the form of direction: Sawppy has no problem dropping from grass to brick, but it takes effort to climb from brick back on to grass. This asymmetry in cost would need to be accounted for.
  • In the upper left corner we see a row of short bricks. An autonomous Sawppy would need to evaluate those short bricks and decide if they could be climbed, or if they are obstacles to be avoided. Experimentally I have found that they are obstacles, but how would Sawppy know that? Or more interestingly: how would Sawppy perform its own experiment autonomously?

  So many interesting problems, so little time!

  (Cross-posted to NewScrewdriver.com)

• ROS In Three Dimensions: Data Structure and Sensor

  Roger • 01/16/2019 at 10:10 • 3 comments

  One of the ways a TurtleBot makes ROS easier and more approachable for beginners is by simplifying a robot’s world into two dimensions. It’s somewhat like the introductory chapters of a physics textbook, where all surfaces are friction-less and all collisions are perfectly inelastic. The world of a TurtleBot is perfectly flat and all obstacles have an infinite height. This simplification allows the robot’s environment to be represented as a 2D array called an occupancy grid.
  

  Of course, the real world is more complicated. My TurtleBot clone Phoebe encountered several problems just trying to navigate my home. The real world do not have flat floors and obstacles come in all shapes, sizes, and heights. Fortunately, researchers have been working on problems encountered by robots venturing outside the simplified world, it’s a matter of reading research papers and following their citation links to find the tools.

  One area of research improves upon the 2D occupancy grid by building data structures that can represent a robot’s environment in 3D. I’ve found several papers that built upon the octree concept, so that seems to be a good place to start.

  But for a robot to build a representation of its environment in 3D, it needs 3D sensors. Phoebe’s Neato vacuum LIDAR works in a simplified 2D world but won’t cut it anymore in a 3D world. The most affordable entry point here is the Microsoft Kinect sensor bar from an old Xbox 360, which can function as a RGBD (red + blue + green + depth) input source for ROS.

  Phoebe used Gmapping for SLAM, but that takes 2D laser scan data and generates a 2D occupancy grid. Searching for a 3D SLAM algorithm that can digest RGBD camera data, I searched for “RGBD SLAM” that led immediately to this straightforwardly named package. But of course, that’s not the only one around. I’ve also come across RTAB-Map which seems to be better maintained and updated for recent ROS releases. And best of all, RTAB-Map has the ability to generate odometry data purely from the RGBD input stream, which might allow me to bypass the challenges of calculating Sawppy’s chassis odometry from unreliable servo angle readings.

  (Cross-posted to NewScrewdriver.com)

• Sawppy on ROS: Open Problems

  Roger • 01/13/2019 at 22:28 • 0 comments

  A great side effect of giving a presentation is that it requires me to gather my thoughts in order to present them to others. Since members of RSSC are familar with ROS, I collected my scattered thoughts on ROS over the past few weeks and condensed the essence into a single slide that I’ve added to my presentation.

  From building and running my Phoebe robot, I learned about the basics of ROS using a two-wheeled robot on flat terrain. Sticking to 2D simplifies a lot of robotics problems and I thought it would help me expand to a six-wheeled rover to rough terrain. Well, I was right on the former but the latter is still a big step to climb.

  The bare basic responsibilities of a ROS TurtleBot chassis (and derivatives like Phoebe) is twofold: subscribe to topic /cmd_vel and execute movement commands published to that topic, and from the resulting movement, calculate and publish odometry data to topic /odom.

  Executing commands sent to /cmd_vel is relatively straightforward when Sawppy is on level ground. It would not terribly different from existing code. The challenge comes from uneven terrain with unpredictable traction. Some of Sawppy’s wheels might slip and resulting motion might be very different from what was commanded. My experience with Phoebe showed that while it is possible to correct for minor drift, major sudden unexpected shifts in position or orientation (such as when Phoebe runs into an unseen obstacle) throws everything out of whack.

  Given the potential for wheel slip on uneven terrain, calculating Sawppy odometry is a challenge. And that’s before we consider another problem: the inexpensive serial bus servos I use do not have fine pitched rotation encoders, just a sensor for servo angle that only covers ~240 of 360 degrees. While I would be happy if it just didn’t return any data when out of range, it actually returns random data. I haven’t yet figured out a good way to filter the signal out of the noise, which would be required to calculate odometry.

  And these are just challenges within the chassis I built, there’s more out there!

  (Cross-posted to NewScrewdriver.com)

• Robotics Society of Southern California (RSSC) January 2019 Meet

  Roger • 01/13/2019 at 08:09 • 0 comments

  Today I introduced my rover project Sawppy to members of Robotics Society of Southern California. Before the presentations started, Sawppy sat on a table so interested people can come by for a closer look. My visual aid PowerPoint slide deck is available here.

  My presentation is an extended version of what I gave at Downtown LA Mini Maker Faire. Some of the addition came at the beginning: this time I'm not following a JPL Open Source Rover presentation, so I had to give people the background story on ROV-E, JPL OSR, and SGVHAK rover to properly explain Sawppy's inspiration. Some of the addition came at the end: there were some technical details that I was able to discuss with a technical audience. (I'll expand on them in future updates.)

  I was very happy at the positive reception I received for Sawppy. The first talk of the morning covered autonomous robots, so I was afraid the audience would look down at Sawppy's lack of autonomy. Thankfully that did not turn out to be a big deal. Many were impressed by the mechanical design and construction. Quite a few were also appreciative when I stressed my emphasis on keeping Sawppy affordable and accessible. In the Q&A session we covered a few issues that had easy solutions... if one had a metalworking machine shop. I insisted that Sawppy could be built without a machine shop, and that's why I made some of the design decisions I did.

  A few people were not aware of Onshape and my presentation stirred their interest to look into it. There was also a surprising level of interest in my mention of Monoprice Maker Select v2 as an affordable entry level 3D printer, enough hands were raised that I signed up to give a future talk about my experience.

  (Cross-posted to NewScrewdriver.com)

• Sawppy Will Be Presented At RSSC

  Roger • 01/11/2019 at 00:50 • 0 comments

  I brought Sawppy to the Downtown Los Angeles Mini Maker Faire this past December, where I had the opportunity to give a short presentation about my project. Also at the event were the Robotics Society of Southern California (RSSC) and a few members asked if I would be interested in presenting Sawppy at an upcoming RSSC meeting.
  

  Since I’m always happy to share Sawppy with anyone interested in my little rover, I said yes and I’m on their calendar for the RSSC meeting on Saturday, January 12th. From 11AM to noon, I plan to talk for about 35-40 minutes and leave the remaining time for Q&A and drive Sawppy over obstacles to demonstrate the rocker-bogie suspension.

  This group has collective expertise in Robot Operating System, which I’ve been learning on-and-off at a self guided pace. If conversations go in a direction where it makes sense, I’ll be asking my audience for their input on how to best put Sawppy on ROS. I also plan to bring Phoebe, my ROS TurtleBot clone that I built to learn ROS, just for fun.

  And I’m sure I’ll see other cool robotics projects there!

  (Cross-posted to NewScrewdriver.com)

• Sawppy Post-Faire Cleanup

  Roger • 12/04/2018 at 00:54 • 0 comments

  When I work on Sawppy, I test and run indoors. At DTLA Maker Faire Sawppy ran all over, both indoors and out. Most of the time people were playing with Sawppy on a piece of artificial turf at Maguire Gardens. This is an outdoor space where people would walk their dogs, raising obvious sanitation concerns running Sawppy on my home carpet after the event.
  

  Well, after a long day of work, who doesn’t enjoy kicking off their shoes and soaking their feet? I could give Sawppy the same royal treatment. All six wheels were removed and soaked in a tub filled with a mixture of water and household bleach. A retired toothbrush was used to scrub off dirt particles clinging to the wheel. Hopefully this removed most of the contaminants Sawppy might have picked up during the event.

  It was also a good time to perform an inspection to see how Sawppy held up mechanically. In addition to the set screw mentioned yesterday, a few chassis mounting screws have fallen out and need to be replaced. I designed plenty of redundancy in these mounts so there was little risk of Sawppy falling apart.

  After a few hours of soaking, the wheels were hung up to dry like old socks. What has six rover wheels but is not a rover? This laundry rack.

  (Cross-posted to NewScrewdriver.com)

• Sawppy at DTLA Mini Maker Faire

  Roger • 12/03/2018 at 04:50 • 0 comments

  Yesterday Sawppy went on an adventure to the downtown Los Angeles Mini Maker Faire. There Sawppy found a receptive and appreciative audience. There were a lot of enchanted kids, interested parents, and other makers who might be building their own Sawppy rovers.

  The morning started out with Sawppy sitting on a table alongside a few different builds of JPL open source rover. Eric’s build is on the left in black and white, Santa Susana High School build is on the right with purple printed parts.

  Taking Sawppy around and talking to individuals about Sawppy was a lot of fun and something I’ve done in other contexts before. I have hopes for a few of the contacts to develop into something cool for Sawppy’s future. What’s new this time was that I also signed up to give a short 15-minute presentation about Sawppy and that took more work and preparation. Thanks to the 2-minute “lightning talk” opportunities at Hackaday LA the past few months I’m less nervous about public speaking than I used to be, but I still got pretty stressed about it. I’m sure it’s a matter of practice and the more I can take advantage of such opportunities the better I’ll get.

  Outside of the presentation, Sawppy and I spent most of our time on the astroturf across the walkway from the officially assigned display area. It was a hilly part of the park which meant there were no tables or booths set up there, and it was a good place to demonstrate rover suspension in action. I had a spare phone set up to be Sawppy control and handed the control to anyone who wanted to pilot Sawppy for a bit.

  Most were content to run around the turf. Some of the little ones tried to run Sawppy into their siblings. A few ran into the bushes beyond the turf for a more rugged demonstration of Sawppy chassis. A perpetual favorite is to have Sawppy climb over shoes.

  Thanks to refinements to improve robustness over the past few months, Sawppy came out of the experience with only a slightly wobbly left rear wheel that was easily repaired by tightening the set screw on the left rear steering servo coupler. A great improvement over earlier outings!
  

  (Cross-posted to NewScrewdriver.com)

• Sawppy Will Be At DTLA Mini Maker Faire

  Roger • 11/26/2018 at 19:45 • 0 comments

  The Downtown Los Angeles (DTLA) Mini Maker Faire, hosted at the Los Angeles Public Library central location, is coming up this weekend and my rover Sawppy will be among the many maker projects at the event.

  Sawppy will be one of several rovers present. JPL’s Open Source Rover team should be there with their original build, SGVHAK will be there with the beta build rover I contributed to, which inspired my Sawppy and they’ll all be hanging out together.

  The JPL team will also be giving a brief presentation in the KLOS Children’s Theater upstairs about their rover project, followed by an even briefer presentation by me on building Sawppy. Both of these talks are listed on the workshop schedule though (as far as I know) there is no hands-on workshop activity planned. Sawppy will be present and running for people to see up close, but no assembly (and certainly no disassembly!) is planned. I may bring an extra corner steering unit for people to play with, and they’ll be welcome to take that apart and put it back together, but not much beyond that.

  (Cross-posted to NewScrewdriver.com)

• Sawppy Sees Brief Internet Fame

  Roger • 11/20/2018 at 19:05 • 0 comments

  A few days ago I noticed a sudden spike in internet traffic to Sawppy – page views on my personal blog, Sawppy’s Hackaday.io project page, the Github repo, and YouTube video all rose dramatically. It took a little digging around various statistics reporting pages to figure out where the interest was coming from. Answer: someone had submitted Sawppy to Hacker News giving Sawppy a brief taste of internet fame.

  Given the general attention span of the internet at large, the traffic disappeared just as quickly as it came. But in that brief moment in time, a few thousand people spared a few seconds (or more) of their lives to look over Sawppy and that’s more than what I had before.

  And this bit of exposure might lead to other interesting projects down the line. It seems to have caught the eye of someone with interest in the Pi Wars robot competition. Sawppy’s current configuration is indeed controlled by a Raspberry Pi, but according to contest rules Sawppy is too big to fit as-is. I’m not sure a six-wheeled rocker-bogie suspension would be useful for any contest objectives (challenges) in Pi Wars. But it would absolutely make my day if I see one of the competitors downscale Sawppy to fit in the size envelope, thereby creating a “Sawppy Jr.”
  

  https://twitter.com/pinski1_/status/1061997311843287041

  (Cross-posted to NewScrewdriver.com)
  

• Daniel Perron's Sawppy

  Roger • 08/10/2018 at 19:55 • 1 comment

  I saw that RaspberryPi.org had an article on JPL Open Source Rover. In the comments section, there was a comment by Daniel Perron (who had also commented on this project page) mentioning Sawppy. I think Daniel should have a project page for his own Sawppy but I haven't seen one under his Hackaday.io account. 

  Which is a shame, because his rover is making good progress and his work totally deserves attention. So I'm going to draw attention to his build on my Sawppy page here.

  Here's a scaled-down copy of the image he linked from his RaspberryPi.org comment. From this picture I can see a few changes from my design. The biggest change is in the structural beams. Daniel is using something other than the Misumi 3-series 15mm extrusion that I used. I'm curious to see how well these beams work. Their uninterrupted square profile should make Daniel's Sawppy more rigid than mine, and more rigidity is always good.
  

  And here's his YouTube clip showing his travel motor turning a wheel under control of his own servo control code.
  

  I'm super excited to see another Sawppy taking form. Your rover looks great, Daniel! Great job and I look forward to seeing your future progress.

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