Sawppy the Rover

Description

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!

Details

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.

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! 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.

Files

Sawppy V1 Schematic.png

Bare bones Sawppy version 1 schematic

Portable Network Graphics (PNG) - 192.78 kB - 03/13/2019 at 06:14

Preview

Download

Components

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.

Project Logs

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Sawppy Builders (Page 2)
Roger • 08/23/2019 at 07:48 • 1 comment

For Sawppy Builders 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.

... and more rovers still yet 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.
Instructions Posted For Running SGVHAK Rover Software on Sawppy
Roger • 03/31/2019 at 19:48 • 0 comments

I had always intended for Sawppy to be an adventure in building autonomous robots, but the Sawppy hardware I built and declared version 1.0 needed software of some sort in order to get up and running. Since I had code for SGVHAK Rover handy, I adapted it to control Sawppy as well. Both rover models had six wheel drive and four wheel steering resulting in large overlaps of functionality. I only had to write adapter code for it to communicate with Sawppy’s LewanSoul serial bus servos instead of SGVHAK Rover’s RoboClaw motor controllers.

At the time I was overly optimistic about how quickly I could get new software up and running on Sawppy. I didn’t climb the learning curve for ROS nearly as fast as I had hoped, requiring detours along the way to build learning robots like Phoebe. In the meantime Sawppy continued running on this “interim” software that threatens to become the permanent software with each passing day.

A symptom of optimism was my decision to not write very much documentation helping other Sawppy builders adapt SGVHAK rover software to run on their own rover. I thought I would have new software soon so why bother? At first this was not a problem – first three Sawppy builds I’m aware of were built by people who made modifications and used their own methods of rover control. (Two are writing their own software, the third was modified for standard remote control.)

But now I’m starting to receive queries from people who want to run SGVHAK rover code on their Sawppy rovers as well. While a talented few have been able to find their own way just by examining my Github repositories, it’s not very friendly to tell people “Go look at the code and figure it out.” I need to put in the time to write instructions for putting SGVHAK Rover software on Sawppy.

I’m happy to announce that this work is now complete and posted up on Sawppy’s build documentation repository. It walks through assigning unique IDs to LewanSoul serial bus servos, to which configuration files to edit, and which configuration files to just completely overwrite. I hope this will help more Sawppy builders get their rover up and running!
(Cross-posted to NewScrewdriver.com)

View all 39 project logs

Build Instructions

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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.

Discussions

Marco Walther wrote 10/16/2019 at 15:56

A little update on my Sawppy. I added the Intel RealSense T265/D435 cameras ( https://www.intelrealsense.com/depth-camera-d435/ https://www.intelrealsense.com/tracking-camera-t265/ )and I'm playing with ROS[1] on it now. I can drive it via ROS nodes and the rover behaves pretty much as before. I got both cameras to report in the correct frame yesterday. Now I have to get it to map some rooms;-)

https://www.bytesalad.org/~marco/sawppy_eyes.jpg

https://www.bytesalad.org/~marco/sawppy_rviz.jpg

https://github.com/mw46d/Sawppy_ROS

Are you sure? yes | no

Patrick wrote 10/13/2019 at 21:12

Swappy, my take on the Sawppy rover design, was a huge hit in the Mini Maker Faire Rocklin! Here's a photo of it at the event: http://www.patronics.org/swappy.html Unfortunately I was kept too busy answering questions to remember to take any other photos of it, but it was so much fun meeting other people interested in it, hopefully inspiring some to try similar projects on their own!

I did have a few repair sessions to retighten the set screws on the wheels, so I'll definitely be trying your suggestions of loctite and making bigger detents on the axels https://newscrewdriver.com/2018/06/20/improve-motor-shafts-with-larger-flatter-detents-and-apply-loctite-to-set-screws/

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Roger wrote 10/13/2019 at 21:35

Congratulations on a successful outing! I frequently find myself facing the same problem you encountered: have so much fun talking to people about the rover we forget to take pictures. But as far as problems go, that's a pretty good one to have, right?

I look forward to reading about your upcoming modification experiments.

Are you sure? yes | no

Marco Walther wrote 10/16/2019 at 15:44

I was thinking about the Mini Maker Faire Rocklin;-) But we had fun with a High Altitude Balloon launch & recovery on that Saturday;-)

Too much fun and too little time:-(

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Patrick wrote 10/07/2019 at 23:00

I've finally just about finished my Sawppy rover, (mine's nicknamed Swappy), after finally fixing an insideous electrical glitch that kept killing the Teensy Microcontrollers (I'm also using @Marco Walther's design for the wheel driving). Everything's functional except 2 of the steering motors (the connectors for making a longer cable are in shipping now), but it works well enough to drive even without the other motors.

I'm also experimenting with allowing it to be controlled over long ranges over the cellular network! Photos and/or videos coming soon, it's difficult to film it and drive at the same time, and waiting on finishing the last two steering motors.

I'm so thrilled with it so far, thanks so much for inspiring me with Sawppy at Maker Faire Bay Area @Roger!

Are you sure? yes | no

Steve wrote 08/12/2019 at 01:22

I finally have my Sawppy built and am starting on the electronics and compute build-out.
It has a body, now it needs a brain:
https://drive.google.com/file/d/1DdWZY4xo6N1cITnRVAw_B5MOwnU0gL9O/view?usp=sharing

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Roger wrote 08/12/2019 at 03:21

It looks great! I love the green color, the picture makes it look translucent like Jade. Are you using @Marco Walther design for wheel drive actuators? Looking forward to seeing it run.

Are you sure? yes | no

Steve wrote 08/12/2019 at 04:19

Yes, I'm using the same DC motors he is. Probably the biggest challenge so far has been the holes for the heat-inserts. All the models I printed out, the holes were too big and the inserts were pulled out under tension or they just didn't seat correctly to begin with..So I've made them smaller with OpenSCAD.

Also, I've printed out the axles and drive shafts using NylonX at 100% infill.
We'll see if that holds up. So far the Rocker and Bogie shafts are all bearing the weight fine and the set-screws seem to bite into the shafts nicely.

Are you sure? yes | no

Marco Walther wrote 08/12/2019 at 05:56

I can't see a reply link on Steve's last comment:-( Not sure, the longer heat inserts worked well for me. https://www.mcmaster.com/94180a333

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Marco Walther wrote 04/22/2019 at 04:15

A little night excursion into the backyard;-) https://www.youtube.com/watch?v=rvCmtjlanaQ

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Roger wrote 04/23/2019 at 19:11

Wow, how are the bright yellow pieces glowing like that? Are they UV-reactive and you installed UV LEDs on board?

Are you sure? yes | no

Marco Walther wrote 04/23/2019 at 19:56

The filament (and paint) are UV-reactive, yes. But I just had an external UV CFL (normally used for Halloween;-) for illumination. I do have UV LEDs (from other projects), but since most events are during daylight, I did not see the need to add them to my rovers;-)

Still without Sawppy, but my rovers plot to take over the world;-) https://www.bytesalad.org/~marco/RoversPlotToTakeOverTheWorld.jpg

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Marco Walther wrote 04/21/2019 at 22:52

I never posted in this thread:-( I do have built a Sawppy as well and I'm very happy with it;-)

https://cdn.hackaday.io/images/original//2983811547403540755.jpg (Sawppy on a planet far far away;-)

In the meantime, I replaced the drive servos with 25D geared motors with encoders. That should help with switching the software to a more ROS-based setup.

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Roger wrote 04/21/2019 at 23:14

Welcome to the public discussions Marco! I think your motor replacement project holds a lot of promise, looking forward to hearing how ROS integration works out.

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Marco Walther wrote 04/22/2019 at 03:10

It might just have to wait until after MakerFaire Bay-Area. I'm kind of busy into then.

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lmckeega wrote 04/21/2019 at 05:05

Hi Roger. I just finished the initial build of my version of Sawppy. I am still working on the electronics and have designed a PC board to mount everything. I started a project page at https://hackaday.io/project/165094 and will document some things that I am doing differently.

My plan is to add detail to the body to make the rover look as accurate as possible to the Curiosity rover.

I took the rover 'off roading' today. There is a video of the trip at the link above.

Many thanks for your work on this project. Without your work and sharing, I would not have been able to complete a project like this.

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Roger wrote 04/21/2019 at 23:13

Congratulations on getting your Sawppy up and running! It's always a lot of fun for me to see one running around, climbing over things. I look forward to seeing your enhancements to make your rover look more like the real rover Curiosity.

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W. James Dittmar wrote 04/20/2019 at 10:00

+1 I just built this as well. Great job on this project Roger.

Here is a link to a video I made of it: https://www.youtube.com/watch?v=vTzPXhKfGCg

Couple of thoughts/questions:

1. What is the purpose of the differential brace? I can't seem to figure out what it is supposed to do. It is a big part so I decided not to print it. It seems like everything works without it.

2. If you are scared of using hand power tools to cut steel at home (like I am) you can use a hacksaw to cut the steel bars. It takes about five minutes to cut through a bar. On a related note, you can also use a hacksaw to cut the grooves for the retaining clips. Just put the shaft in a vice, do a couple swipes perpendicular to the vice with the hacksaw, then rotate the shaft a couple millimeters and repeat.

3. You used a cheap 3D printer (about $200). I also took this approach and bought a used Ultimaker Original for about $300. It looks like you ended up spending another $100 to upgrade the hot end. I spent hours and hours fiddling around with the printing settings, making adjustments in the model, filing / sanding / hammering parts to get them to fit together well. Amidst all of this I purchased an MK3S kit for about $700. Everything printed perfectly with no changes in the settings and printed several times faster. You may want to point out that you may save a couple hundred dollars by getting a cheap 3D printer, but you are going to pay for it by fiddling around with your cheap printer for many hours. I also noticed that the better precision that you can get with the better 3D printers results in more structural integrity of the PLA. My parts were much stronger when I printed them with the exact same infill and the exact same model with the better printer. PLA is actually pretty strong and it should not fail at the loads it will be carrying in this thing. The only advantage of PETG would be that it is more resistant to heat.

Again, great work. I found this project because I was originally going to build the JPL open source rover, but then realized I didn't want to spend $5,000 to develop something that extremely over-engineered to drive around in my back yard :)

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Roger wrote 04/20/2019 at 20:43

I'm always happy to see more Sawppy rovers taking shape and running around. Thanks for sharing the video!

To answer your question: the differential brace helps distribute load along the length of the differential rod. If your Sawppy equipment bay is lightly loaded and/or well balanced, it would indeed work just fine without a brace. (Or if you use a very strong material for your differential rod.) But as you add to your rover, you'll start seeing the differential bar bending under load.

And thank you for sharing your tips about the hacksaw, plus additional confirmation that cheap 3D printers always end up demanding we spend more time to address their problems. There's no free lunch here, it's always a tradeoff.

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W. James Dittmar wrote 04/24/2019 at 11:51

Ah, ok that makes sense with the differential brace.

Side question: how did you learn to design this and your other projects? I would like to learn how to build these types of electromechanical systems. Do you have any formal background in mechanical engineering? Did you just kind of look at the JPL rover design, eyeball everything in CAD, test, and iterate? I am trying to figure out whether I would be able to build stuff like this with a top down approach (learning other people’s designs, building, experimenting), or whether I need to take some courses in mechanical engineering to have some formal background.

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Roger wrote 04/24/2019 at 19:03

I have no formal background in mechanical engineering, just experience gained from design, test, and iterate. While there's value in learning some lessons first hand vs. from a book, I'm sure a formal background would have cut down on the number of mistakes I've made. Fortunately for people like us, 3D printers have made mechanical design/test/iterate much faster and cheaper, letting us learn by doing without dying of old age or going bankrupt.

I would summary my position as this: formalized mechanical engineering background would be useful, but willingness to design/test/iterate is critical. Don't get discouraged when the first few attempts don't work, everybody goes through that. Learn something from the experience and try again.

For your amusement, here's a picture I took showing every... "lesson"... on my way to the version 1.0 rover you see on this project page. https://newscrewdriver.com/2018/07/16/road-to-sawppy-is-paved-with-plastic/

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Phillip wrote 04/11/2019 at 23:45

Add another SAWPPY to the list of functioning builds. Just finished assembling mine and other than a few typo's I made in the configs, it works fine.

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Roger wrote 04/12/2019 at 00:34

Great to hear! Do you have pictures to share? I'd like to see if I may.

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Phillip wrote 04/12/2019 at 00:48

https://photos.app.goo.gl/BBwUz1vXgLVmb3LeA

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Roger wrote 04/20/2019 at 20:21

Your Sawppy looks great, Phillip! I love the red & black color theme.

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lmckeega wrote 02/25/2019 at 03:37

Hi Roger,

I am really having a good time working on this project. Your work on it is very inspiring.

I think I have the electronics figured out but have a problem with programming.

I've loaded the program on a Raspberry Pi and it runs fine, but I am having trouble figuring out how to make it work with any motor except roboclaw. The way I read it, I need to change the config_roverchassis.json file to replace "robocloas" with "lewansoul". When I do this I get a 'unknown motor control type' error. I also tried to change it to 'adafruit_servo' with the same results. Can someone point me in the right direction?

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Roger wrote 02/25/2019 at 06:30

Which branch of SGVHAK_Rover repository are you in? The 'master' branch is focused on SGVHAK rover. Sawppy code like the LewanSoul support class lives in the 'development' branch. As for the JSON file itself, please see config_sawppy.json for example. On my Sawppy's local clone of the repository, config_sawppy.json is copied over config_roverchassis.json.

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Roger wrote 03/25/2019 at 07:28

FYI I have merged all changes from 'development' to 'master' branche in order to avoid any future confusion. I was also alerted to a problem with default config files published on Github, which I have just fixed. (Thanks Martin!)

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lmckeega wrote 02/14/2019 at 23:31

Hi Roger,

I am also a beginner to robotics and the Raspberry Pi. I would like to build a Sawppy Rover and have started some of the printing and purchasing. I don't have a problem with any of the printing or construction, but would like a little more information on how the electronics are configured. Could you include a list of the electronics boards/components that are required? I am a programmer, so feel that I can figure out the programming, but it is unclear what parts I need.

Thank you.

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Roger wrote 02/25/2019 at 06:34

Sorry I didn't see your question earlier. Judging by your follow-up question, you've figured it out but I'll post an answer for future readers: 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.

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jsa2010 wrote 02/25/2019 at 18:18

Thanks Roger this is exactly what I needed, perfect timing! I’m building Sawppy with my kids, and this was the only bit that I wasn’t quite sure of. We still have lots of printing and building ahead of us before we even get there. Thanks for an awesome project! The $ difference between JPL OSR and Sawppy is enabling our 3 kids (elementary, middle, and high schooler) to build and program this at home and really get excited about STEM, robotics and exploration. Thanks again!!

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Roger wrote 03/13/2019 at 06:23

I've also just posted a schematic for everyone to reference.

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aanandbajaj wrote 02/08/2019 at 23:41

Hello Roger,

I'm a beginner to robotics. Do you suggest I start with other smaller projects first before this one? Also, what resources would you recommend to someone who is new to this area?

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Roger wrote 02/11/2019 at 21:10

While I worked to make Sawppy as easy to build as I could, it is still a robot with a multi link suspension system and moving it requires coordinating ten motors. There are more beginner-friendly robots with just two motors driving wheels with no suspension.

That said, if simple robots are too boring to hold your interest, by all means dig into something challenging enough to motivate you. The "best" robot will be different for everyone. As long as you are learning as you go, because the learning is what matters.

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Bob wrote 11/29/2018 at 18:16

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

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.

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Bob wrote 11/29/2018 at 20:05

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

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

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

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Roger wrote 10/10/2018 at 00:55

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

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Bob wrote 10/10/2018 at 01:15

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.

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

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.

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Roger wrote 09/17/2018 at 20:06

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Sawppy the Rover

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