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• Sawppy at Caltech Science for March 2019

  Roger • 3 days ago • 0 comments

  Today Sawppy joined the fun at Science for March 2019, organized by the Caltech Postdoc Association. Since Sawppy didn’t exist yet during 2018’s event, this was Sawppy’s first visit. When Sawppy arrived at South Campus Gate, a quick check of campus directory oriented us to Beckman Mall where the event will be held.

  Part of the journey included crossing picturesque Millikan Pond.

  As with last year’s event, the rover started the day sitting on a table for display. Of course, last year we had only a single rover. This year we have three, two of which were in running condition and could be driven for demonstration today.

  Sawppy attracted a crowd as it usually does, and were driven around by enthusiastic children. Some of them weren’t as gentle with the control as they should be, and about halfway through the day, operator roughness by one of the kids burned out the fuse. I kept telling myself I should have spare fuses in Sawppy’s first aid kit that I keep in my backpack, but I never did put one in. I had to hack a workaround today but by the end of the night I definitely remembered to put extra fuses in the bag.

  Group rover outings are always fun. Today’s special activity is a group climb on a grassy slope at the north end of Beckmann Hall. SGVHAK rover gave Sawppy a head start, but with faster and more power motors, combined with better traction tires, it was no contest. SGVHAK easily outclimbed Sawppy, but the important part was that we pleased the crowd with this little demonstration of rover climbing capabilities.

  (Cross-posted to NewScrewdriver.com)

• Sawppy 1.0 Wiring Schematic

  Roger • 5 days ago • 0 comments

  When I declared Sawppy the Rover has reached version 1.0 and posted instructions online, I was fully aware of the fact that the instructions would be incomplete. Not out of neglect or malice, but out of the fact all of Sawppy is in my head and there will be places where I decided something was obvious enough not to require documentation – and learn I was wrong in that judgement.

  Such is the case now. One member of RSSC accepted my invitation to build a Sawppy after my presentation in January, and submitted the feedback that I need to post a schematic of how I’ve wired up Sawppy. I previously submitted this answer as response to a comment on this Hackaday.io project page, but more detail was needed.

  The minimum electronics components for a bare-bones Sawppy has [10 * LewanSoul LX-16A] wired in parallel with each other and to [1 * LewanSoul “BusLinker” a.k.a. “Debug Board”] to translate generic USB serial to servo half-duplex serial. That translator board is connected to [1 * Raspberry Pi] via USB.
  

  I thought this was a good opportunity to try Scheme-It from Digit-Key. It is a web-based electronics schematic editor that purports to let people quickly sketch up electronics schematics for sharing. The electrical wiring for a bare-bones Sawppy version 1.0 should be a nice easy exercise for this tool.

  The terms and conditions for using Scheme-It is fairly typical for a web-based application. A Digi-Key account is required for login, something I already had from earlier purchases for electronics experiments. In exchange for free use of the software, a user also has to grant Digit-Key a license to the schematic. Not a big deal in this case, as I wanted Sawppy to be shared as widely as possible. And finally, Digi-Key reserves the right to take down this service at any time, deleting all of my data. This is irritating but not unexpected. If this is important to me I better make a copy for my own storage.

  Since my sample schematic is fairly simple, it only took about an hour to go from absolute beginner to the schematic I wanted to create. I could (and did) choose to share the project file publicly via a URL, though it appears accessing the project requires logging in to Scheme-It, which required a Digi-Key account as previously mentioned. I could also export to PDF or PNG formats. The PDF export feature was unsatisfactory. Many labels were moved out-of-place making the schematic illegible. In contrast the PNG export looks OK so I’ve posted this schematic PNG to the files section of this project page, as well as Sawppy’s assembly instructions hosted on Github.

  (Cross-posted to NewScrewdriver.com)

• Sawppy at SCaLE 17x: The Trouble with Rovers

  Roger • 03/12/2019 at 04:59 • 0 comments

  My primary obligation for Southern California Linux Expo (SCaLE 17x) was to co-present The Trouble with Rovers with Lan Dang on Saturday afternoon. Which meant when Sawppy’s coupler broke Friday evening I had to scramble to fix it for Saturday. A rush repair job is always going to leave some details to be desired but it was sufficient to resume operation.
  

  Sawppy will obviously be one of the visual aids present at our talk, but that doesn’t mean it gets to spend the rest of the day just sitting around. No sir, as soon as Sawppy arrived on location, it immediately started working as a roving billboard for both itself and the talk.

  It was not explicitly coordinated beforehand, but the SGVHAK rover was also equipped with advertising for our talk. Both of our rovers were out and about, pulling roving billboard duty, and occasionally our paths crossed in the hallways of SCaLE.

  I was happy with the turnout for our rover session. While we did lose a few people who left partway through the talk, it was more than made up for by the enthusiastic people who followed along and came up to ask questions after. I had a lot of fun explaining details on what we did for both rovers, minutiae that we trimmed from the talk proper but was still interesting to our smaller and more technical audience afterwards.
  

  Sawppy continued to roam around Pasadena Convention Center, spreading word of my rover project to people who are excited about the possibility of building their own. Some people thought it would be their motivation to finally buy their own 3D printer, others have all the tools on hand and it’s just a matter of prioritization and finding project time. I was most gratified by a group of students from California State University San Bernardino who thinks it would be a great group project. They are exactly the target audience!

  And it’s fun as always to see young children’s faces light up when they see Sawppy, some of whom were eager to take control. My favorite was this 6-year old who loved to drive Sawppy over his own toes over and over.

  (Cross-posted to NewScrewdriver.com)

• Cracked Sawppy Steering Coupler Almost Survives Full Day of SCaLE 17x

  Roger • 03/10/2019 at 20:09 • 0 comments

  Before I took Sawppy to its first day of SCaLE 17x, I checked over all mechanical bits and found a cracked steering coupler. My first instinct was to repair my rover by replacing the coupler, but I decided against it because it was still partially functional. I wanted to see how my rover design behaves with some partially broken parts, find out how tolerant of faults it would be.
  

  The answer is: surprisingly well! When everything is in newly assembled condition, the steering assembly could keep its wheel steering angle within a few degrees of the desired position. There is still some error due to flex in the PETG plastic through all component interfaces leading from the servo’s output shaft, through the coupler, through the 8mm steering shaft, through the steering knuckle, through the wheel bearing, the bearing axle, and finally the wheel itself.

  With a cracked steering coupler, the steering assembly could still hold angle within about a 20 degree range, or +/- 10 degrees of the desired position. This isn’t great, but like its Mars inspirations, Sawppy was able to keep running with a damaged wheel. I was able to do the usual crowd-pleasing demonstrations running over backpacks and feet. While steering was a bit wobbly, Sawppy has five other wheels to compensate and maintain most of its steering authority.

  I thought I’d just continue running the rover until something finally gave. And it did, just not the way I expected. Instead of a gradual degradation in rover operation, what finally killed the coupler was a child. About 6-8 years in age, the boy grabbed the steering wheel assembly in both hands and twisted hard. I heard a loud POP and that was the end of the coupler. The boy knew he was going to be in trouble and ran off, the associated adult was apologetic, but that doesn’t change the fact I now have a broken rover.

  Here’s a picture from yesterday, with a partially failed coupler:

  After abuse by careless child, here’s a fully failed coupler:

  Yesterday the coupler was cracked below the set screw. Now the crack goes all the way to the top and there’s no longer enough force to hold the heat-set insert in place. Once the heat-set insert popped out of place, its set screw no longer has leverage to grip the detent I cut on the steering shaft. A steering shaft that spins nearly freely makes Sawppy very hard to drive. I was able to move a little bit at the Tindie x Hackaday Birds of a Feather Session, but Sawppy could not perform its usual rover capability demonstrations at the meetup.

  (Cross-posted to NewScrewdriver.com)
  

• Sawppy Steering Coupler Volunteers For Fault Tolerance Test

  Roger • 03/08/2019 at 20:39 • 0 comments

  Whenever I’m getting Sawppy ready for a public appearance, I power up my rover and drive it around a bit to make sure all the mechanical bits are functioning. I did the same for preparation for Sawppy’s appearance at SCaLE 17x and I saw the right front wheel – historically the most problematic part of any rover – is wobblier than I expected.
  

  This usually indicates a set screw is backing out, something that was much reduced after I started using Loctite on the set screws. But when I reached towards the coupler with a wrench to turn the set screw, I realized this situation is different. The PETG plastic for the coupler has cracked.

  For context, here’s the non-cropped version of the image to show location of this coupler in Sawppy’s front right wheel assembly.

  This is a new failure! And a bit of a surprise, too. My experience with PETG to date has been that it is very tough and willing to flex instead of break like my experience with PLA. It’s held up well through multiple public appearances, driven by enthusiastic children who were none too gentle with the rover. It appears we have finally reached the breaking point for PETG.

  Or… have we?

  The rover is still driving and nominally functioning. System performance has degraded but strictly speaking, the system has not yet failed. The crack allowed more movement in wheel steering than designed, but the movement is still constrained instead of turning freely out of control. I would call the latter case, which happened to Sawppy earlier, an actual failure. This isn’t quite it.

  And now I’m curious about what potential stages of system degradation will be, so I’m going to leave the cracked coupler in place for now. I will build a replacement and have it on hand for a field repair, but the cracked coupler has just volunteered itself for a test of Sawppy fault tolerance. How much further can Sawppy go on a cracked coupler?

  (Cross-posted to NewScrewdriver.com)

• Sawppy and SGVHAK Rover will be at SCaLE 17x

  Roger • 03/07/2019 at 20:02 • 0 comments

  This year's Southern California Linux Expo (SCaLE 17x) begins today. Four days of talks across multiple tracks focusing on topics relating to the flagship open source operating system in various ways. From small micro controllers to large cloud infrastructure. Last year's SCaLE served as deadline and motivation for completing SGVHAK Rover, but it was only for purposes of show and tell. We couldn't yet do a full presentation as the JPL Open Source Rover project has yet to officially launch until mid year.
  

  But that is no longer a concern, and we even have spinoff projects like my Sawppy rover to add to the mix. Hence Sawppy will be part of our SGVHAK presentation "The Trouble with Rovers": they're never really finished, and their numbers keep growing. Rovers are such cool projects to work on there's always more upgrades and evolution we can perform to make our rovers better. Lan and I practiced this talk at last month's SGVLUG meetup and hopefully our presentation will be better for it! We'll be presenting Saturday afternoon 4:30-5:30pm in Ballroom G.

  Sawppy will also be present at the Tindie+Hackaday Bring-a-Hack meetup, under their "Birds of a Feather" event umbrella for groups to get a space and meet. It is a free event (with at least a SCaLE Expo Pass) and Sawppy will be there as representative of one of the projects with a page on Hackaday.io. This will take place Friday evening 7pm-8pm in Ballroom B.

  Beyond those events, Sawppy will be generally hanging out and cruising about the event and the expo floor. There'll probably be some time spent at the SGVLUG/SGVHAK booth, but no official scheduled events beyond the two above.

  (Cross-posted to NewScrewdriver.com)

• Sawppy at Brawerman East STEAM Makers Fair

  Roger • 03/06/2019 at 22:58 • 0 comments

  Sawppy’s next publicity appearance was at Brawerman East STEAM Makers Fair, a supercharged science fair at a private elementary school. Sawppy earned this invitation by the way of January presentation at Robotics Society of Southern California. The intent is to show students that building things is more than their assignments at their on campus Innovation Lab, there are bigger projects they can strive for beyond the classroom. But the format is, indeed, just like a school science fair, where Sawppy got a display table and a poster board.

  But Sawppy is not very interesting sitting on a table, it didn’t take long before the rover started roving amongst other exhibits. The school’s 3D printer is visible on the left – a Zortrax M200.

  Sawppy was not the only project from grown-ups present. I admire the ambition of this laser cutter project undertaken by one of the parents. Look at the size of that thing. It is currently a work in progress, and its incomplete wiring were completely removed for this event so little fingers are not tempted to unplug things and possibly plugging them in a wrong place.

  The center of this tables had some old retired electronics equipment that kids will be able to take apart. This was a huge hit at the event, but by the end of the night this side of the room was a huge mess of tiny plastic pieces scattered all over.

  I brought my iPad with the idea I could have Sawppy’s Onshape CAD data visible for browsing, but it turned out the iOS Onshape app required a live internet connection and refused to work from cache. As an alternate activity, I rigged it up to show live video footage from Sawppy’s onboard camera. This was surprisingly popular with the elementary school age crowd, who got a kick out of making faces at the camera and seeing their faces on the iPad. I need to remember to do this for future Sawppy outings.

  After Sawppy was already committed to the event, I learned that a Star Wars themed art car was also going to be present. So I mentioned my #rxbb8 project which earned me a prime parking spot on the first floor next to the far more extensively modified “Z-Wing.” Prepare to jump to hyperspace!

  (Cross-posted to NewScrewdriver.com)

• Sawppy at Space Carnival Long Beach

  Roger • 02/21/2019 at 22:25 • 0 comments

  Space Carnival, held at the Expo Arts Center in Long Beach, California, welcomed Sawppy as one of several exhibits Monday afternoon. It turned out to be part of a week-long LEGO robotics camp for elementary school students. Most of the events are for campers, but the Monday evening Space Carnival was open to the public.

  Since the focus is on LEGO, there were plenty of plastic bricks in attendance. The middle of the room had a big pile of bricks on a plastic tarp and kids were crawling all over the pile building their creations. Sawppy mostly spent time outside of the tarp, occasionally venturing on to some of the colorful game boards for LEGO robots to line-follow and other tasks.

  As usual, I handed controls over for kids in attendance to play with. Running over feet is still more popular of an event than I can hope to understand but, if it makes them excited, so be it.

  Sawppy was not the only non-LEGO robot in attendance, there were also a selection of Star Wars licensed merchandise including this R2D2. I forgot if this particular unit was made by Sphero or Hasbro.

  This event was not the first time I crossed paths with Barnabas Robotics, but it was the first time I got to speak with them beyond the standard sales pitch type of discussions. Since their business is STEM education for students K-12, they have a good feel of what type of material is appropriate for various age groups. It’s possible Sawppy can find a role in high school curriculum.

  (Cross-posted to NewScrewdriver.com)
  

• Sawppy Has A Busy Schedule This Week

  Roger • 02/11/2019 at 21:14 • 0 comments

  Since the time I declared Sawppy version 1.0 (mechanical maturity), I’ve been taking my rover out to various events. From casual social gatherings to large official events to presentation in front of others who might appreciate my project. Sawppy has been a great icebreaker for me to start talking with people about their interests, and sometimes this leads to even more events added to Sawppy’s event calendar. This coming week will be especially busy.

  On Monday February 11th from 3pm-6:30pm Sawppy will be at Space Carnival, a FIRST Themed Event on Lincoln’s Birthday. Held at Expo Arts Center, a community space in Long Beach, CA. This event is organized by people behind local FIRST robotics teams. This year’s competition is titled “Destination: Deep Space” and has a very explicit space exploration angle to all the challenges. So even though Sawppy is nothing like a FIRST robotics competitor, an invitation was still extended to join the fun.

  This event will be unique in that I had the option to be a roaming exhibit and I chose it for novelty. I think a rover who is roving will be much more engaging than a rover sitting on a table. It also means I will not be tied to a booth, so I could check out other exhibitors as I roam around with Sawppy. This eliminates the problem I had with Sawppy at DTLA Mini Maker Faire – I had to stay in one place for most of the event and couldn’t see what other people had brought.

  On Wednesday February 13th Sawppy will join a STEAM Maker’s Fair at Brawerman East, a private elementary school. This is a small event catering to students and parents at the school. I believe the atmosphere will be similar to a school science fair, with exhibits of student projects. To augment these core exhibits, Sawppy and a few others were invited. The intent is to show that concepts covered in their on-campus Innovation Lab projects are just as applicable to bigger projects outside of their class.

  And finally, on Thursday Februarh 14th Sawppy will be part of another SGVLUG presentation. A follow-up to the previous rover themed SGVLUG presentation, this will still set up background but will talk more about what has happened since our initial rover construction. This also serves as a practice run for a presentation to be given at Southern California Linux Expo (SCaLE) next month.

  (Cross-posted to NewScrewdriver.com)

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

  Roger • 01/16/2019 at 22:28 • 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)

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