Sawppy the Rover

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:

Motorization: Instead of using gearmotors with encoders managed by RoboClaw motor controllers, moving the wheels will be done with serial bus servo motors.
Construction Method: Instead of using the Actobotics construction system, Sawppy will be built from Misumi 15mm 3-series aluminum extrusions beams connected by 3D-printed plastic parts.

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.

Since the time I declared Sawppy version 1.0 (mechanical foundation) complete and posted assembly instructions, others have built on top of what I've released to the world! They're outlined in the project log "Sawppy Builders" entries, page 1 and page 2 with more to come as I hear about more rovers.

Project Logs

Collapse logs

Rhys Mainwaring’s ROS Melodic Software and Simulator for Sawppy
Roger • 01/31/2020 at 22:37 • 3 comments

When I created Sawppy, my first goal was to deliver something that could be fun for robotics enthusiasts to play with. The target demographics were high school students and up, which meant creating a software stack that is self-contained and focused enough to be easy to learn and modify.

To cater to Sawppy builders with ambition for more, one of the future to-do list was to write the necessary modules to drive Sawppy via open source Robot Operating System. (ROS) It is a platform with far more capability, with access to modules created by robotics researchers, but not easy for robotics beginners to pick up. I’ve played with ROS on-and-off since then, never quite reaching the level of proficiency I needed to make it happen.

So I was very excited to learn of Rhys Mainwaring’s Curio rover. Curio is a Sawppy sibling with largely the same body but running a completely different software stack built on ROS Melodic. Browsing the Curio code repository, I saw far more than just a set of nodes to run a the physical rover, it includes two significant contributions towards a smarter rover.

Curio Rover in Simulation
There’s a common problem with intelligent robotics research today: evolving machine learning algorithms require many iterations and it would take far too long to run them on physical robots. Even more so here because, true to their real-life counterparts, Sawppy and siblings are slow. Rhys has taken Sawppy’s CAD data and translated physical forms and all joint kinematics to the Gazebo robot simulator used by ROS researchers. Now it is possible to work on intelligent rovers in the virtual world before adapting lessons to the real world.

Rover Odometry
One of the challenges I recognized (but didn’t know how to solve) was calculating rover wheel odometry. The LX-16A servos used on Sawppy could return wheel position, but only within an approximately 240 degree arc out of the entire 360 degrees circle. Outside of that range, the position data is noisy and unreliable.

Rhys has managed to overcome this problem with an encoder filter that learned to recognize when the servo position data is unreliable. This forms the basis of a system to calculate odometry that works well with existing hardware and can be even faster with an additional Arduino.

ROS Software Stack For Sawppy
Several people have asked me for ROS software for Sawppy, and I’m glad Rhys stepped up to the challenge and contributed this work back to the community. I encourage all the Sawppy builders who wanted ROS to look over Rhys’ work and contribute if it is within your skills to do so. As a ROS beginner myself, I will be alongside you, learning from this project and trying to run it on my own rover.

https://github.com/srmainwaring/curio

(Cross-posted to NewScrewdriver.com)
Sawppy Builders (Page 2)
Roger • 08/23/2019 at 07:48 • 1 comment

This is the second page of Sawppy Builders, for Page 1 click here.

Steve (jetdillo)

I met Steve at Maker Faire Bay Area 2019 in May, where he showed me pictures of a few of his Sawppy parts. It is now August 2019 and his Sawppy is mechanically complete. Steve is a HomeBrew Robotics member like Marco, and the new rover is neon green to distinguish from Marco's neon yellow Sawppy.

In terms of modifications, Steve is adopting Marco's faster wheel drive motors, and instead of cutting drive shafts from metal Steve has printed his from NylonX. It'll be interesting to see if that material is strong enough for the job!

See more details at Steve's YASP (Yet Another Sawppy Project) page.

Leif Sorgule

Leif is teaching a robotics course for high school students and he thought Sawppy might be an interesting team project for the class. The class will start with the Arduino control option, given cost and learning resources available for Arduino. It'll be fun to see what the students dream up for their own Sawppy modifications.

Patrick Leiser
Patrick's Sawppy variant (named Swappy) made an appearance at the Rocklin Mini Maker Faire, representing the Sierra College Robotics Club. It might be the first of Sawppy's siblings to be chauffeured around in a Tesla Model 3, though this picture shows it doesn't quite fit in the frunk.
TeamSG Aussie Sawppy
Sawppy has a brother down under! This is a father-and-son team putting a rover together, and their chosen yellow-and-black color scheme looks very sharp.
... and hopefully more rovers to come!
Sawppy at Maker Faire Bay Area 2019
Roger • 07/28/2019 at 23:53 • 0 comments

I took some footage of Sawppy's adventures at Maker Faire Bay Area 2019 and assembled them into three videos.
It was raining at the event, so Sawppy needed to put on a raincoat before venturing outdoors:
It was the first time Sawppy attended a three-day long event and one of the steering servos failed on the third day.
After the event, Sawppy needed some cleaning and minor repairs.
Curiosity Rover 3D Resources
Roger • 06/25/2019 at 20:52 • 0 comments

Prompted by a question on the JPL Open Source Rover web forum, I compiled all the 3D resources I had collected on Mars rover Curiosity. This reference data helped Sawppy match Curiosity's overall proportions and suspension geometry, which was my goal of making a mechanically faithful motorized model. I stopped there, but others rover builders like @lmckeega are working to improve accuracy in appearance so I thought I'd share these resources to assist such efforts.

3D web sites

My starting point was JPL's official open source rover website whose opening animation has a 3D model of Curiosity cruising on a simulated Mars surface. I tried to extract that 3D mesh without success.

On a similar front, we could see a 3D model of Curiosity in the "Experience Curiosity" website. It's possible this is using the exact same data set as the OSR, but still I'm not enough of a web developer to pull out the 3D data.

Finally we have a 3D model visible on Curiosity's mission site. Again it may or may not be the exact same one used in above two sites, but the difference here is that we have a "Download" button. Clicking that button results in a file named Curiosity_static.glb. My laptop running Windows 10 has a 3D Viewer app installed by default, which was able to view this file. I don't know what viewer software would be required for other platforms.

3D printing

A web search for "Curiosity 3D Model" and similar keywords would repeatedly lead me to a 3D-printable static model. Unfortunately, for my purposes this model is not useful. The geometry of this model were modified to be friendly to 3D printing and is not a faithful representation of Curiosity.

3D animation

However, on the same site, there are two Curiosity models for the free open source 3D animation program Blender. As far as I can tell, these two models have the same 3D data but with different textures. "Clean" is factory fresh Curiosity, and "Dirty" represents Curiosity after cruising on Mars for a while.

The advantage of these files is that suspension parts are separate elements that can be animated to show suspension articulation. I believe these files formed the basis for Gazebo simulation described here.

It also means we can split parts apart for a closer look. However, this file only has enough detail for animated graphics, it does not have enough detail for CNC machining. Much of the surface detail are represented by bitmap textures instead of 3D mesh data.

While there is not enough detail for building a high fidelity model, these files were the best resource I had to measure component sizes and their relative layouts. I was able to bring them up in Blender, switch to orthographic projection view, and get images of Curiosity free of perspective distortion. In case that's useful to anyone, and you don't want to install & run Blender just to obtain those images, here they are:

(Cross-posted to NewScrewdriver.com)
Wired Joystick Controller With Arduino
Roger • 05/24/2019 at 00:37 • 2 comments
As a presenter it was great to see the wealth of information provided by Maker Faire Bay Area organizers. It is clearly the compilation of many years of experience and lessons learned. One item caught my eye: anyone using wireless communication should have a contingency plan in case wireless fails.
I've definitely encountered this before with SGVHAK Rover and Sawppy on the standard 2.4GHz WiFi band. So far I've been able to avoid most problems by adding a dual-band router and moving up to the 5 GHz band, but in a large event like the flagship Maker Faire, even that might not be enough.
So as part of my Maker Faire prep work, I designed and built a wired joystick controller with an Arduino as the microprocessor. When active, it replaces the Raspberry Pi and wireless router on board Sawppy. This also serves as a lower-cost alternative to rover builders or those who like the thought of walking their rovers on a leash.
More resources:
- Arduino sketch is in the 'arduino_sawppy' directory of Sawppy's Github repository.
- 3D-printed enclosure Onshape CAD document.
- Build log entries:
  - Getting started with Arduino crash course.
  - Examining Arduino sample code by LewanSoul for LX-16A serial bus servos.
  - Putting Arduino joystick sample code together with LewanSoul sample code for joystick-based servo control.
  - Implementing the Ackermann steering calculation for rover corner wheel steering.
  - Switching to a compact Arduino Nano board to fit in handle.
  - Designing the 3D-printed enclosure.
  - Building Sawppy's onboard input jack.
  - Up and running and ready for Maker Faire!
Sawppy Will Be At Maker Faire Bay Area 2019
Roger • 05/10/2019 at 19:43 • 0 comments

I know I've said I wanted to keep my Hackaday.io project page focused on rover design and evolution and less on rover adventures in the wild... but I'm going to break my own rule for this one. I'm super excited to have been accepted as a maker presenting their project at Maker Faire Bay Area 2019. It's not just A maker faire... it is THE maker faire. Most of my travel logistics have been nailed down, it is happening!
Sawppy Builders (Page 1)
Roger • 05/07/2019 at 23:03 • 0 comments

I started my Sawppy project in March 2018. By May 2018 I had my first rolling chassis but it was fragile. Every time my rover broke, I learn a little more about mechanical design, and Sawppy improved over the following months. I also started writing assembly instructions and supporting documentation to help any other interested people build their own Sawppy, not knowing if anyone would take me up on my offer. It was extremely gratifying to see other people have indeed accepted my invitation!

This post recognizes those who have embarked on their own Sawppy adventures, roughly in the order of when I learned about their efforts. Sometimes I learn about their ambitions before they got started, sometimes I learn about it only after their rover had been completed. Given this, it is likely there are other Sawppy builders out there I don't know about at all! But that's fine, I just love the fact there are more Sawppy rovers running around.

I used to list a few Sawppy builders in my main project description page, but the list has grown too long to fit in that space. I'm going to track Sawppy builds on this project log entry, editing it as I go to add more rovers as they come online. I don't know if there'll ever be a day when even this is too unwieldy to track all the Sawppy builds out there... but as far as problems go, that's one I would be very happy to have.

To everyone who decided my project was worth your own time and money and effort to build: Thank you.

Roger

Daniel Perron

Daniel was one of the first to jump in and start exploring the information I had released. Daniel also helped spread the word of Sawppy via comments on various web page comments about JPL's Open Source Rover, and for that I'm grateful.

I designed Sawppy to use Misumi aluminum extrusions because I saw Misumi had distributors worldwide. Unfortunately my hope of easy availability turned out to be wrong in Canada. But makers are problem solvers! Daniel redesigned his Sawppy to use wooden beams instead.

Quinn Morley

Quinn is a person who thinks big. Quinn has been working to scale up Sawppy's design, making modifications as needed, for a much larger rover. This picture shows one of his big wheels next to a standard sized Sawppy wheel. This rover will be a mobile testbed for his project developing deep ice drilling techniques.

Bob Krause, Inventor Studios

Bob leads a FIRST Robotics team and they have their own version of Sawppy's CAD file filled with their improvements for a better fit with what they want their rover to do. They can't use their rover in an actual FIRST competition because I didn't design Sawppy around competition rules. However, the team members are thinking about using Sawppy's construction technique for their future projects. All of this makes me extremely happy.

Chris Dakin

Sawppy has a sibling in the UK! During Sawppy's evolution I had to adjust various pieces and occasionally aluminum extrusion lengths. This resulted in some recuts and some unnecessary (in hindsight) waste. When I documented their final dimensions, I thought it was possible someone could cut all the required pieces out of two extrusion beams at the 2 meter standard length sold by Misumi. Thanks to the build log for Chris' Sawppy, I saw this hypothesis has been proven.

Marco Walther

Marco has lots of robot building experience and wanted to add a Sawppy to his robot army. I received many helpful pieces of feedback about my posted instructions for Sawppy, pointing out where I could...
Read more »
Magnetically Attached Flag Pole
Roger • 04/09/2019 at 21:56 • 0 comments

One of the problems I didn’t foresee in designing Sawppy was that some children might see a fun challenge in doing running jumps over my rover. I first saw this unwelcome behavior when I brought Sawppy to Long Beach, and I knew it’d only be a matter of time before a child would misjudge their jump and smash Sawppy into a pile of broken rover pieces.

Clearly I need to find some way to discourage this behavior, but I also can’t do anything that physically harms misbehaving children. This eliminates straightforward solutions such as a Samurai blade pointing straight up. I would also like this countermeasure to be stealthy and not call attention to its anti-jump purpose otherwise some would see it as a challenge.

The answer came while preparing for this year’s Southern California Linux Expo (SCaLE 17x). I was scheduled to host the Hackaday x Tindie Birds of a Feather meetup, and I was also slated to co-present a talk with Lan Dang. For publicity purposes I decided Sawppy can be a rolling billboard, as SCaLE is exactly the right audience of people who would pay attention to a 3D-printed rover running about. I pulled out a yardstick I had on hand and started planning how to use it as a flag pole, and I immediately knew I had my anti-jumpover countermeasure as well. Two birds, one stone.
As previously mentioned, I didn’t want this flag pole to be too rigidly attached. If someone bumps my sign, or if someone decides to try jumping over my rover anyway, the flag pole must break away cleanly without damaging the person or the rover. For SCaLE I used a zip tie that was arranged so there is tension holding the yardstick flag pole in place, but pops free when stressed.

This mostly worked, but as it was built on a balance of opposing forces, it was finicky to reinstall. At Caltech Science for March, a curious toddler yanked off the flag pole and the toddler’s supervising elderly adult tried to reinstall the pole. But grandpa had no idea what he was doing, blindly stabbing inside Sawppy’s equipment bay with the yardstick applying more force as he grew more agitated. After two attempts at saying “Don’t worry, I’ll put it back myself” while I watched in horror at Sawppy electronics getting pummeled, I forcibly grabbed the yardstick from his hands in order to save Sawppy from being stabbed to death.

Clearly, a better solution must be found.

In preparation for Sawppy’s appearance at Yuri’s Night, I decided to try a magnetic mounting system. Originally rejected because I thought it wouldn’t be strong enough, I thought it was worth a second look. I had a stack of these powerful little magnets and a single pair wasn’t able to hold the pole. But four pairs of them might be strong enough for the task.

For this test, four magnets were held on to chassis beam via packing tape. Two on upper beam, two lower.
Matching sets were held to yard stick flag pole with more tape.
With updated camera mast and flag pole mount, Sawppy was ready for its next public appearance at Yuri’s Night Los Angeles! That event got crowded at times and there were a few accidental bumps that triggered a clean separation followed by quick re-installation. And while this adult-focused event had few children about, there were plenty of drunken misbehaving adults. The flagpole did not discourage all misguided behavior, but it has worked well enough to become a permanent fixture of my future Sawppy public appearances.
(Cross-posted to NewScrewdriver.com)
New Camera Mast for Kinect V1
Roger • 04/08/2019 at 19:12 • 0 comments
When Sawppy first started running around, I wanted something to sit atop a camera mast where the real rover has a camera and sensor array. It is the anthropomorphic head of the rover and it looks slightly wrong without one. (Like a chicken running around without its head.) The first iteration of camera mast sensor array enlisted a standard USB webcam sitting alongside a Google AIY Vision kit. It was mostly for appearance because there wasn’t much software behind it.

The webcam was fun for entertaining children and occasional longer distance driving, but not immediately useful for autonomy. The AIY Vision box is optimized for classification tasks. I thought there might exist code useful for robotic visual localization but if it’s out there I have yet to find it.

The most promising tool at hand for rover localization is my Kinect sensor bar running RTAB-Map or some similar software. So Sawppy will inch towards autonomy by getting a camera mast upgrade to my Kinect V1 sensor bar and see if we can integrate that into rover systems in a useful way.

I went looking for a good way to mount a Kinect bar to Sawppy. I disassembled its base looking for a good mounting mechanism, but there weren’t convenient existing fasteners for me to use and there weren’t good places for me to drill and tap new ones. It was surprisingly crowded in there! I knew there was a motor for up/down tilt but I underestimated size of the motor gearbox inside.

I then reassembled the base and went with plan B: a simple flat platform for attaching my Kinect sensor bar with double-sided foam tape.

Kinect sits slightly offset camera mast center for two reasons.
1. The Kinect sensor bar is very wide and if mounted centrally it overhangs to the right. I worry about it hitting obstacles so I wanted to bring it closer to the middle.
2. By offsetting sideways, I could expose the top of the pipe used as camera mast and run Kinect’s wire down the middle for cleaner wire management.
At the moment this Kinect is no more functional for autonomy than the previous configuration… in fact, for its first public appearance at Yuri’s Night 2019 it is not even electrically connected to anything. It’s just a matter of taking one step at a time.
(Cross-posted to NewScrewdriver.com)
Yuri’s Night LA 2019
Roger • 04/08/2019 at 00:35 • 0 comments

I'm happy to see interest in Sawppy continue to grow and my little rover now has something of a publicity appearance schedule. Summaries of the past few appearances have been cross-posted on my personal blog as well as this project page, but going forward I think I should keep this project page focused on technical evolution and skip the non-technical stuff.
As the first implementation of this new policy, here's the summary for Sawppy's attendance at Yuri's Night Los Angeles 2019. Anyone who's interested can follow the link to read more, others can skip this log entry without having to do a lot of scrolling.