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Sawppy the Rover

Motorized model of Mars rovers Curiosity, Mars 2020

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Sawppy is a motorized model whose layout and proportion mimics that of Mars rovers Curiosity and Mars 2020. It faithfully reproduces the suspension kinematics of real rovers and is intended to be a hardware platform for future software projects in autonomous operation. Go forth and boldly explore the back yard, Sawppy!

Sawppy the Rover was inspired by JPL's Open Source Rover project. Most of the differences between Sawppy and its JPL inspiration were motivated by a desire to reduce cost and complexity. JPL's rover is designed for education, to be assembled by a school team and give a robust foundation for structured curriculum. Sawppy is more suited for individual hobbyists like myself who are happy to tinker and willing to make some trade-offs to lower cost.

The budget was $500, and getting there required the following changes:

These two major design goals can be summarized as: Servo Actuated Wheels, Printed Interconnect For Extrusion. The acronym SAWPIFE led to the nickname "Sawppy".


See the "Links" section for pointers to additional information:

  • Live Onshape CAD file: This is where I'm tweaking and building Sawppy in full public view. Be warned the live file has upsides (latest ideas!) and downsides (latest idea doesn't work!)
  • Github: This is where the assembly instructions currently live. It also has a snapshot of Sawppy components in STL file format. These parts may lag behind the live CAD data, but they have been printed, installed, and proven to work on my rover.
  • Build Blog: The history of Sawppy, including stories of design goals and lessons learned from failures.

It's been a few months since I declared Sawppy version 1.0 (mechanical foundation) complete and it's very exciting for me to see people build on top of what I've released to the world!

  • Bob Krause (Inventor Studios): A few of Sawppy's parameters were changed for this variant. Instead of just manually editing individual numbers, Bob & crew put in the work to make Sawppy more configurable. Updates to specific parameters are automatically propagated to affected parts. See comments section for Bob's description.
  • Quinn Morley Mars Drill: This project explores the idea of robots drilling for water on Mars. A scaled-up variant of Sawppy serves as the initial testbed mobile drilling platform.
  • Daniel Perron's Wood Beam Variant: When I designed Sawppy, I didn't know how easy or hard it would be to procure parts outside the United States. According to Daniel, the Misumi extrusions are really expensive in Canada. But he is resourceful with experience in woodworking, giving us a delightful variant.

  • 3 × 1 kg spool of 3D printer filament Exact amount of filament used will depend on slicer settings, see "Instructions" section.
  • 10 × LewanSoul LX-16A Serial Bus Servo Design also can be adapted to use Dynamixel AX-12A or Herkulex DRS-0101
  • 3 × Box of 100 M3 * 8mm hex bolts Fastening 3D-printed components to aluminum extrusions
  • 3 × Box of 100 M3 hex nuts Fastening 3D-printed components to aluminum extrusions
  • 3 × Box of 100 M3 washers (< 10mm diameter) Fastening 3D-printed components to aluminum extrusions. Design can accommodate up to 10mm diameter washers, larger washers will require modifying CAD file.

View all 16 components

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

    Roger7 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

    Roger01/16/2019 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

    Roger01/13/2019 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

    Roger01/13/2019 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

    Roger01/11/2019 at 00:50 0 comments

    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

    Roger12/04/2018 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

    Roger12/03/2018 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

    Roger11/26/2018 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

    Roger11/20/2018 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

    Roger08/10/2018 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.

View all 18 project logs

  • 1
    New Home for Sawppy Build Instructions

    After a loss of data event for instructions posted to hackaday.io, Sawppy the Rover's build instructions are now hosted on Github.

View all instructions

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Bob wrote 11/29/2018 at 18:16 point

Roger, this is an exceptional project. 

I've been following developments since your first post announcing Sawppy back in May. We ordered the components soon after, though didn’t start printing the parts from the public OnShape design until about a month or so ago. The printing and assembly processes were very straight-forward with only a few mild surprises.

The aspect of this project that caught our attention is how we’ve been able to bring into our lab off the shelf raw materials like uncut lengths of extruded aluminum beams, nuts and bolts from McMaster-Carr, FDM filament, and very straight-forward drivetrain components and control systems to construct a functional bot of this scale.

I'm a life-long techie. We've taught 3D design classes and camps in East Bay schools, and been working in our garage-based 3D design lab for about 5 years. And yet, we've learned so many tips, tricks, geometries, and processes from this project.

The community that's developed around our lab is composed primarily of teenagers who design and race drones, hack scooter and skateboards, and design useful objects that they sell on eBay to earn what they need for the 5 to 10 projects they have going on at any given time. Many of these kids are also involved with FIRST robotics competitions, FTC and FRC. So when they saw the Sawppy rover come together, they didn't see a Curiosity model as much as a set of design toolkit on which to base their next generation competitive robots.

So... We've begun evolving a copy of the OnShape Sawppy design document. So far, all the changes we've made in our version is backward compatible with yours. Our focus at this point is to increase the configurability of the design, as you can see in the list of changes we’ve made so far that’s included below. 

* Wheel width can be changed
 - Wheel width changeable
 - Steerable knuckle width varies with wheel width
 - Fixed knuckle width varies with wheel width
* Wheel rim and tire can be printed as separate parts of a dual-extrusion printer job
* Beam width & height can be changed
 - All 3D printed components that accept beams varies based on beam dimensions
* LX-16A brackets now accept heat-sets so that servos are held more tightly

* The geometry of the LX-16A bracket changed. 
 - The orientation of the servo is rotated 180 degrees to fit narrow knuckles and narrow tires.

The area we’re focusing on next is support for drive-train and control systems that will move the bot much (much) faster than the LX-16A servos currently allow. The first step in that direction is to design in FTC-compatible (First Technical Challenge) components, which we have an almost endless supply of parts laying around the lab. Driving a bogie suspended robot around on rough terrian at high speeds will likely require adding shock dampeners to the suspension. 

Our longer-term aspiration is to create a more flexible robot design tool that allows designers to create robots with different dimensions, drive-trains, suspensions, control systems, and accessories.

We’ve made our copy of the OnShape document public. It’s named SawppyRover.neobobkrause. You can link to it here… https://cad.onshape.com/documents/aaa3eec885d174f48744d770/w/a9ccb2ae8a9fa3bfab65a3f5/e/02e39956ce53a7a4a720a4aa

We would like all changes made to your design to be shared and merged so that there continues to be a single design used by all, if you're open to that.

Roger, thanks once again for all the work you put into this design and for documenting the design and releasing it to the community. It’s awesome.

- Bob Krause

Inventor Studios

Berkeley, CA

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Roger wrote 11/29/2018 at 19:46 point

Wow, Bob, this is fantastic! I love the changes made to make Sawppy parameters more configurable. I'm open to the idea of having one integrated CAD file, but I just spent 15 minutes on Onshape documentation & forums and failed to find a way to merge changes made in a copy back to the master. (A "pull request" in Git parlance.) I'd love pointers to documentation to do so if you know of any.

In the meantime, I'll add links to your variant's Onshape CAD file. Have you guys documented your project on hackaday.io or elsewhere? I could add links to that, too.

I was just in the SF Bay area last week, I should have stopped by Inventor Studios. Oh well, maybe another time.

  Are you sure? yes | no

Bob wrote 11/29/2018 at 20:05 point

OnShape is a useful tool, though it's still just a shadow of its big brother Solidworks. OnShape has the capability to merge forked versions within a single document, though not across two documents, even if one document started out as a copy of the other. 

The good news is that I made a copy of your original document on 10/2/18. It appears that you haven't modified your version since 9/17/18. So if you're comfortable with the changes we've made, we could just use our version as the master version going forward.

From this point on, you could make a copy of my document that you would own, then control edit permissions for designers who you approve (like us). Then you and I and any other approved designers will make changes to this single document. The checkin process each team would go through would involve merging its changes with any other changes that have been checked in.

Thoughts?

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Bob wrote 11/29/2018 at 20:43 point

Here are some shots of some wheels and knuckles we've printed that are narrower (65mm). One wheel has a TPU tire on a PLA rim. The other rim was printed using transparent PETG. The third photo shows the narrow fixed knuckle from the inside. Also note that the orientation of the servo has been rotated 180 degrees.

(Can images be added in comments?)

https://www.dropbox.com/s/u8qaj90vdefdtd8/IMG_5790.jpg?dl=0

https://www.dropbox.com/s/w68ovzi40b3lyi3/IMG_5789.jpg?dl=0

https://www.dropbox.com/s/r89cadrrx283x9m/IMG_5787.jpg?dl=0

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Bob wrote 10/09/2018 at 14:44 point

Is there any firmware for the rover? Even an incomplete codebase would be valuable and allow builders to evolve the code forward.

  Are you sure? yes | no

Roger wrote 10/10/2018 at 00:55 point

I'm working towards making Sawppy work with the open source Robot Operating System. As an interim solution, my rover is running the code I wrote for SGVHAK Rover but configured to send commands to Sawppy's LewanSoul serial bus servos. 

https://github.com/Roger-random/SGVHAK_Rover/blob/development/config_sawppy.json

  Are you sure? yes | no

Bob wrote 10/10/2018 at 01:15 point

Roger that. ;-) 

I'm still printing. And given everything else on our plates, may be for awhile. We'll first print your reference design and get it running with the LewanSoul servos. But we're really here to explore how a modified rover architecture would handle itself in the FIRST Robotics ring. Yes, that would involve looking at rigidity, drive train, firmware, scalability, configurability, durability, stability, and 5 other flavors of 'ability. But have you seen Erector Set pieces and decade-old electronics most commonly used on FTC bots?

Thanks for putting your design out for all to explore. You've done a terrific job. It's exciting to have the OnShape geometry available to configure. As somebody coming at this as a 3D'er, we really like it when we have full control of the geometry to configure based on our needs.

  Are you sure? yes | no

Quinn Morley wrote 09/15/2018 at 15:42 point

Roger, how much scale-ability do you think there is to be had by merely changing the length of the aluminum extrusion and changing the wheel diameter? I want to create one approximately the same size as Curiosity to use as a testbed. 

  Are you sure? yes | no

Roger wrote 09/17/2018 at 20:06 point

Sawppy is approximately 1/4 scale of Curiosity. When scaling up, the first limitation will be the servo motors I used. I tried them with a 1/3 scale wheel and they struggled to climb modest obstacles, so an actual-size rover will need more powerful motors. I haven't experimented beyond 1/3 scale so I don't know for sure what else will be problematic, but here are my guesses: 

(1) 15mm extrusion beams start twisting along their axis. Possible solution: use larger extrusion beam profiles like 60mm or alternate structural members.

(2) 3D printed connectors deform under load. Possible solution: print with very rigid materials like carbon fiber infused nylon.

(3) 8mm steel drive and steering shafts start bending. Possible solution: larger diameter shafts and corresponding larger bearings.

Personally my 1/4 scale rover already takes up too much space at home and barely fits in my car's seat for transport. I admire your goal of going full size, that's huge! (I mean that both as a compliment and literally.) Whether you end up using my Sawppy design or not, please document your project online. I'd love to watch as it progresses.

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Quinn Morley wrote 09/18/2018 at 07:29 point

Great answer. I'll think about the wheels and wheel motors. Your plastic parts may work if we scale them up for 60mm extrusion, they should have a much higher stiffness. Different motors, shaft diameters etc would be the biggest obstacle. I'll post the project when I get started. I really appreciate your feedback and love your design! Thanks again.

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Dongwon Lee wrote 09/14/2018 at 06:09 point

Hello. Thank you for nice 3D modeling of Mars Rover. I started to print out each parts. I'm considering electric configuration. First of all is power. How much power will be need per 1 servo?. I will use 5200mAh 2S 30C battery..  the other thing is motor/control balance. 10 servo+ 1 controller  or 5 servo + 1 controller at each left/right side .. which one is better?

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Roger wrote 09/17/2018 at 19:38 point

Your battery will be more than adaquate. The LewanSoul LX-16A servo I used drew a little over 1A when stalled at maximum effort. In the worst case (and hopefully very unlikely) scenario with all ten servos stalled, that's over 10A. Let's say 15A to be conservative. A 5200mAh 30C battery can withstand peak draw of 5.2A * 30 = 156A, so your battery can provide peak power over ten times what's needed.

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Roger wrote 09/17/2018 at 19:42 point

All the motor control power management circuit is built in to the LewanSoul LX-16A servo so each motor has their own controller. The LewanSoul "debug board" controller is primarily a serial communications translator so a single one will be fine for the entire servo network.

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todbot wrote 07/09/2018 at 22:15 point

Hi Roger,  it was great chatting with you at the SGVHAK BBQ. We talked a bit about traction add-ons for Sawppy's wheels.  I'm sure you've already considered this, but I've always admired the O-rings on the original Big Trak as a cheap & repairable solution. I found these 4" diameter ones on McMaster that are 50 for $12. https://www.mcmaster.com/#9452k192/=1dn5rr1

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Roger wrote 07/12/2018 at 23:56 point

That's a nice and inexpensive venue to explore. I'll start brainstorming what kind of rover wheel I could build with these rings. Thanks for the pointer!

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Daniel Perron wrote 06/05/2018 at 11:23 point

I love what you did and  I start to made my own  with my 3D printer. All the wheel are done using PETG and I'm doing the  boogie wheel right now. I'm missing the aluminium extrusion dimension but I will use wood stick cut from my bench saw instead.  I still missing a lot of 3D printer parts so I suppose that the dimension will show itself when I put all pieces together.  I did create a python3 class object for the LX16A.  I will refine that class to add the missing catch exception handler.  https://github.com/danjperron/LX16A    

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Roger wrote 06/05/2018 at 17:20 point

Thanks for letting me know you're building one. It's very encouraging to hear! As you've noticed it's still a work in progress with incomplete information, but I'm happy to expedite filling in information holes on request. Since you would like aluminum extrusion dimensions, I've filled in the "Components" section with extrusion beams and their lengths. Let me know if you need anything else.

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Daniel Perron wrote 06/16/2018 at 02:34 point

I start to learn little by little onshape.  I did change your servo coupler. I'm using 12mm M3 flat head hex screw and I change the length of  the servo coupler  to 8mm instead of 10mm. This way I could use the 12mm screw to attach the  coupler  with the provided adapter to the LX16A motor.  https://imgur.com/a/rRuu83O. I also grind a part of the wheel to be able to  tight the lock screw of the wheel using allen key.

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Roger wrote 06/17/2018 at 19:10 point

Great work! Have you considered creating a Hackaday.io page for your Sawppy build? I'd love to see you detail your modifications. Why you made them, and how well they worked. Together we will keep improving the design in the spirit of open source!

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terence.d.healy wrote 05/17/2018 at 15:18 point

Excellent rover and very nice work.  I'm very interested to hear how you are using the servo motors rather than gear motors with encoders. Can you tell us about the software a bit? Do you use ROS - if so, what computing hardware? 

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Roger wrote 05/17/2018 at 16:29 point

I do have ambition to put ROS on Sawppy and give it some autonomy, but for now I'm still working on the chassis hardware. At the moment Sawppy's brain is a bare-bones piece of software that allows simple tele-operation and runs on a Raspberry Pi. (Translation: right now it's just a very expensive remote control car.) Code is up on Github, search for "SGVHAK Rover"

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John Whitten wrote 05/16/2018 at 19:21 point

Awesome. I am both intrigued and jealous. I applaud your good efforts and eagerly await your next developments. 

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