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Row-bot

Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
edited 2016-06-23 13:44 in Robotics
This semester my students are designing model boats. As team projects they have been tasked with designing an RC paddlewheel catamaran. They have to design and loft the pontoons, make sure the volume displacement is adequate, align the center of gravity with the center of buoyancy, cut the hull, deck, fin, and paddlewheel pieces out on the laser cutter and assemble everything. At the end of the semester, they will race them in the local marina. Here's a video of the prototype I made as a feasibility study:



It uses a pair of Parallax continuous-rotation servos, and RC receiver, some gearing, and an aluminum shaft to drive the paddlewheels. Here's a photo of the innards of the sealed electronics box:

row-bot_gears.jpg

After doing this, I thought it might be fun to replace the paddlewheels with oars. Here's a video of the "Row-bot" in action:



The oars operate via a homemade ball-joint drive, illustrated here:

row-bot_ball_joint.JPG

I told the kids they could do a Row-bot in lieu of the paddlewheel variety, if they wanted to. It might be fun to pit paddlewheels against oars in the race. We'll see what they choose ...

-Phil
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Comments

  • ercoerco Posts: 20,244
    Sure sounds awesome, but I can't see either video, just white space.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2016-04-20 05:54
    Erco,

    Sorry, man. D*** forum software! I wish Parallax would prioritize fixing what's still broken after -- how many months has it been now?

    Here are the links:




    Please let me know if this works better.

    -Phil
  • Wow! that is the best Robo Platform ever, The kids are going to love it, Great design all around.
    Not sure which I would pick, The Row Bot for speed, or the Paddle Wheel for the coolness factor.
    I want to sign up for Phils class.

    I think if you eliminate a couple of paddles from your wheel, you could gain some speed. strange but true.
    At high speed, too many paddles will cavitate and slow the craft down, it's weird science, check it out.
    Angle of attack, depth of paddle, length of stroke, all kinds of engineering involved in a paddle wheel.
    Way more than I thought when I started messing with them.

    -Tommy
  • ercoerco Posts: 20,244
    Both are friggin' awesome! How nice that we both posted Paddlewheel bots just a few hours apart. One if by land, two if by sea!

    Like Tommy, I'd love to be in your class. For extra credit, I'd make a one servo/motor boat!
  • Thanks, guys!
    Ttailspin wrote:
    I think if you eliminate a couple of paddles from your wheel, you could gain some speed. Strange but true. At high speed, too many paddles will cavitate and slow the craft down, it's weird science, check it out. Angle of attack, depth of paddle, length of stroke, all kinds of engineering involved in a paddle wheel. Way more than I thought when I started messing with them.
    Interesting observation. I once tried to make an anemometer with six cups. It didn't work -- perhaps for the same reasons. I'll give it a try with fewer blades. The paddlewheels are super easy to make. They're just laser cut from doorskin and Gorilla-glued together, with a Delrin hub tacked on to mate with the shaft.

    -Phil

  • Row-bot rules the water! I could watch that all day haha.
  • I tried paddlewheels with four large blades instead of the twelve small ones in the original design, and the craft did move faster. Thanks again, Ttailspin, for the insight. 'Just in time, too, since I'll be addressing paddlewheels today in class.

    -Phil
  • W9GFOW9GFO Posts: 4,010
    I really like the rowing version. I do think a microswitch on each servo would be a huge improvement so that you can synchronize the strokes.
  • ercoerco Posts: 20,244
    Ttailspin wrote: »
    At high speed, too many paddles will cavitate and slow the craft down, it's weird science, check it out.
    Angle of attack, depth of paddle, length of stroke, all kinds of engineering involved in a paddle wheel.

    I'm sketching up a one-servo, non-cavitating silent magneto-hydrodynamic caterpillar drive catamaran right now.

  • W9GFOW9GFO Posts: 4,010
    erco wrote: »
    ...For extra credit, I'd make a one servo/motor boat!

    A Yuloh or sculling oar should work pretty well with a one servo boat.

  • > I told the kids they could do a Row-bot in lieu of the paddlewheel variety

    I predict that a lot of them will choose the row boat because it looks so much more interesting. e.g. if you took that and the paddlewheel to MakerFaire which one would people want to control?

    Nice job!
  • ercoerco Posts: 20,244
    KeithE wrote: »
    > I told the kids they could do a Row-bot in lieu of the paddlewheel variety

    I predict that a lot of them will choose the row boat because it looks so much more interesting.

    More interesting and also more work to construct. Many students are slackers (McFly!) and will choose the "least work" option.

  • One thing I forgot to mention is how the pontoons are built. They're lofted in RhinoCAD, which can unroll the developable hull surfaces, which are then laser-cut from a 1/16" single-ply veneer that I was able to score from EdenSaw. The hull is registered and shaped via slots and tabbed bulkheads cut from doorskin. Everything is held together with wire, hot-melt glue, and Super Glue.

    Normally, a model boat builder would then employ epoxy and phenolic powder to fill the external voids between hull pieces, add further coats of epoxy to seal everything, followed by several coats of varnish. This presents a problem for a classroom situation in terms of time and toxicity. So I came up with a quicker, safer way to seal the pontoons: skin-packing. You've probably experienced -- and cursed at -- products that are skin-packed. Basically a heated plastic film is sucked down over the product onto a porous card that's coated with a heat-sensitive glue. I have a friend who has one of those skin-pack machines and was able to get some of the glue that the film sticks to.

    Once the kids are done gluing their hulls, they will coat it with this glue, which is a totally benign, water-soluble product. When the glue dries, I'll take their hulls out to my friend's machine and seal them with the plastic film. BTW, this is the reason for using veneer instead of plywood. Veneer is porous, allowing the vacuum to pull though it; plywood is not.

    So far, I've been happy with the results this process has yielded. The kids just need to make sure they employ enough bulkheads to keep the hull pieces from collapsing in the vacuum.

    -Phil
  • WhitWhit Posts: 4,191
    Unbelievable and absolutely incredible work Phil!
  • Now, If you really want top speed from your Paddle Wheel, You will need a state of the art "Feathering Paddle Wheel",

    It's an interesting mechanism, and Probably not difficult to build, if you have a little skill with a laser cutter... ;)

    Not that a "one-servo, non-cavitating silent magneto-hydrodynamic caterpillar drive", would be hard to build either, but
    You will probably want to have a Drill Press, and maybe some chisels, or at least a good hammer... Tool up! is my motto.

    -Tommy
  • ercoerco Posts: 20,244
    edited 2016-06-23 00:24
    This $2500 Hobie Mirage Eclipse is fabulous and overpriced. I really like the alternating 2-fin drive shown at 0:30 and 1:30. Looks & sounds efficient. Hmmm. Could there be a one-servo row-bot in the offing? :)



    The drive is sold at http://www.austinkayak.com/products/18199/Hobie-Mirage-Drive-GT-ST-Fins.html

    Edit: I see a bike-type chain there... in salt water?
    Photo attached next, cannot add here by edit.
  • ercoerco Posts: 20,244
    hobiedrive.jpg
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  • erco wrote: »
    Sure sounds awesome, but I can't see either video, just white space.


    My problem to, looks like a cool project Phil.
  • Not sure how I missed the first postings of this project. Excellent work Phil!!

    Stemming from your concept is a solution to one of my self-made idea challenges. I have always wanted to make a "hull adapter" that enables a Scribbler S2 to be used as the core of a watercraft. This way, a Scribbler and the Scribbler GUI can be used for a water robot. Your design would completely allow for that! Drop a scribbler into a waterproof enclosure and mate it's wheels to your sealed paddlewheel shafts and you are good to go!
  • Phil,
    Great project, how did the kids do? I am curious what did you use for the water sealed through hull fitting for your electronics box?
    Jim
  • RS_Jim,

    None of the kids opted for an oar-powered craft. Most used three- or four-blade paddlewheels. We held a five-team tournament at a local marina. Each race between two teams consisted of a round-trip from the starting line: a 30-yard straightaway, then around a dock piling, and back. It was windy, and the tide was receding, but the kids' crafts performed quite well, on the whole.

    One of the reasons for my insisting on a twin-hull design was to avoid stability issues, which went beyond the scope of the class. As a consequence, none of the resulting designs had roll-stability problems. However, one team chose to make their pontoons short and deep, which produced a pitch-stability issue so pronounced that their craft could flip upside-down and backstroke through the water.

    The shaft seals on the box consisted of laser-cut rubber washers squeezed between the black Delrin ring shown in one of the above photos and the housing, via six screws. It protected against incidental splashing but leaked a tiny bit when submersed by the upside-down craft.

    Here are some photos from the race:

    race3e.jpg
    race1e.jpg
    race2e.jpg

    -Phil
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  • RS_Jim,

    None of the kids opted for an oar-powered craft. Most used three- or four-blade paddlewheels. We held a five-team tournament at a local marina. Each race between two teams consisted of a round-trip from the starting line: a 30-yard straightaway, then around a dock piling, and back. It was windy, and the tide was receding, but the kids' crafts performed quite well, on the whole.

    One of the reasons for my insisting on a twin-hull design was to avoid stability issues, which went beyond the scope of the class. As a consequence, none of the resulting designs had roll-stability problems. However, one team chose to make their pontoons short and deep, which produced a pitch-stability issue so pronounced that their craft could flip upside-down and backstroke through the water.

    The shaft seals on the box consisted of laser-cut rubber washers squeezed between the black Delrin ring shown in one of the above photos and the housing, via six screws. It protected against incidental splashing but leaked a tiny bit when submersed by the upside-down craft.

    Here are some photos from the race:

    race3e.jpg
    race1e.jpg
    race2e.jpg

    -Phil

    That's quite inspiring, Phil. I wish I some kids around here would be in to the same. They all seem to be into air,(quads), instead of water.

  • Publison,
    Could it be that air is more redily available than water?
    Jim
  • Has anyone came up with a solution to waterproof a servo, such as a boot. I need something that doesn't take up much space, and the balloon idea just don't appeal to me.
  • ercoerco Posts: 20,244
    @Phipi: Would a watercraft that walks on water get an A in your class?

  • Totally!

    In fact, two of my students from last semester (brothers) own, with their dad (one of my T-bird sailboat partners), a small rowing/sailing dinghy named "Water Strider," named after this beastie:

    https://en.wikipedia.org/wiki/Gerridae

    One of the brothers loosely modeled his paddlemaran deck after said insect. But an actual robotic water strider would be very cool. (Now you're making me wish I were teaching again next school year, instead of taking a one-year break!)

    -Phil
  • @Phil Pilgrim, I have been unable to find suitable paddlewheels online for a project I've wanted to build. They would be perfect for lakes or ponds that have algae or reeds.
    Is there a document where I could get more details about how you built them?
  • Attached is the one my class used.

    It's not very detailed, though, because I wanted the students to be creative in their designs. Most used three- or four-bladed paddlewheels. And I think that's probably the most efficient design.

    -Phil
  • Attached is the one my class used.

    It's not very detailed, though, because I wanted the students to be creative in their designs. Most used three- or four-bladed paddlewheels. And I think that's probably the most efficient design.

    -Phil

    Thank you. I'm a big fan of drones which can move in any direction in any orientation. I'm trying to imagine a radio controlled floating watercraft with those capabilities. The 'ideal' craft would have those abilities even in a gently moving stream.
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