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