• CAD update and some notes about building with 3D-printed parts.

    Steve10/01/2019 at 05:08 0 comments

    I pushed up a bunch of changes to my fork of the Sawppy Repo, that, among other things, include a good number of the models I had to rework because of issues with the heat-insert holes on things like the Steering Knuckle assembly, wheel hubs, etc. being too big. This is not at all a slam on Roger or the work he's done, it's just the current reality of building things with parts made by a printer that doesn't cost as much or more than a new late-model car.

    If you are going to be building something like a Sawppy be prepared to budget for failures, even if the print completes successfully. Things may just not fit right and post-processing may or may not help and you might have to resort to other methods to resolve the situation.  For the Steering Knuckles that provide corner-steering for the rover, I did not re-print them but instead went with #6-32 inserts instead of the 3mm that are used elsewhere in the model.  I would allot a whole extra spool for these sort of problems because printing them out at full-size in your final material is really the only way to figure it out. Resist the temptation to print out things in super-cheap PLA for fit-and-finish because it's going to flow and expand and contract differently than PETG.

    Anyway, that's more of a ramble than I'd planned on about all this.


  • 6 Wheels rolling!

    Steve09/28/2019 at 07:41 0 comments

    I got all the motor pods connected and running tonight. There's a bit of precession going on with a couple of them and I'm not exactly sure what's going on with that. It  could be a wheel or axle that is not mounted entirely flush against a hub or mount or something. I'm going to take them off this weekend and investigate. The important bit though is that I can command each motor pod individually and that all the time I've put into wiring and mapping out the pins and terminals and everything has paid off.  I flipped the switch this afternoon and all the wheels started rolling in the same direction at the same speed, first time off, which is HUGE.

    I'm using 3 LM298N dual motor controllers, hooked up to an Arduino MEGA 2560 via screw-terminal shield.
    That will ultimately be connected to a Pi or maybe even a Jetson that is running ROS.

    For now though, I'm pretty psyched that I've gotten this far. Teleop control is just around the corner,  hopefully sometime in the next week or so, after I get the precession issues sorted.

  • Motor test

    Steve09/26/2019 at 20:52 0 comments

    This is a test of one of the motors after I'd printed out the housing, shafts, etc. and screwed everything down. Mostly I was just going through the full sub-assembly here, checking out how it all moved once assembled. The bracket/housing here is printed in a red PLA because I wanted to save the nicer, slightly more spendy PETG for the actual model vs. using it on a test-stand that would probably get tossed or might break or need another round of CAD & printing if things didn't fit exactly right.


    I generally keep a couple spools of bargain-basement PLA on hand for just this sort of thing. I get the super-cheap $9.99 whatever-Amazon-throws-at-me or what Matterhackers has on clearance and then print all my test-fit parts with that, saving the more expensive stuff for the final print when I'm sure all the fit-and-finish has been worked out.

    Google Drive is being annoying about inlining videos that I've uploaded there. The inFrame method I've used before to include a link to a video I've uploaded to drive doesn't seem to work anymore. So you'll just have to check it out here:

    On-bench motor test



    (If somebody has figured out the current way to inline display videos from Google Drive or something this isn't YouTube/Vimeo, please comment below.
    Thanks!

  • "in media res..."

    Steve09/22/2019 at 20:33 0 comments

    I'm posting this actually quite a ways into the project. I started working on it around March-ish 2019, about the time that the final collapse of TheShop.build(nee' TechShop) happened and I lost access to a metal shop within a reasonable drive of SF.

    So, here we are. My as-yet-unnamed SAWPPY-alike has now been moved to Circuit Launch in Oakland, CA. where I am one of their Roboticists in Residence, focusing on rovers and off-road, ruggedized robots.

    Anyway, here are a few random pics of my build process. My rover was printed on a Raise3D N2+. The wheels are PETG-CF from Matterhackers. The drive axles and steering shafts are NylonX(About which I'll write more later) . The rest of it is printed in PETG from a variety of suppliers.

    All great projects start out on the kitchen table:

    The all-important mechanical "backpack test", when it was still occupying whatever random corner in our apartment I could put it in that night.

    I spent (and am just now finishing) a LOT of time on the wiring. I've built enough robots of significant size to know that organizing and "dressing" your cable runs will save a lot of debug time later.


    Anyway, this is kind of where we are right now. I'm expecting to wrap up the wiring in the next couple days and start some motor tests followed by actual roving Real Soon Now.