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

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.

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.

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

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

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

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

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.

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.

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

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.

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.

+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 :)

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.

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. 

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/

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.

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

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

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

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?

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.

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!)

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.

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.

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!!

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

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?

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.

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

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.

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?

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

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

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

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.

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. 

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.

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.

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?

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.

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.

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

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!

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    

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.

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.

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!

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? 

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"

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