Pedal Boat Design

Discussion in 'Boat Design' started by BG_Geno, May 28, 2006.

  1. BG_Geno
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    BG_Geno Senior Member

    Whoops...forgot 2 things.

    First, this is the type of thing that helps designers Beppe...

    last, we need to call the test tank the Curtis Wet Wheel Lab in honor of our resident model builder/tinkerer and the data sets collected the Willoughby Wheel Data Base in honor of our resident grumpy mathematician =)

    I am willing to build the thing, and to test all your wheels, and to provide the plans and parts list for anyone wanting their own tanks...so come on Guys and help me figure out the details.

    G
     
  2. Guest625101138

    Guest625101138 Previous Member

    BG
    The problem with tank testing like this is that you only have the static condition. This is not too bad for the paddlewheel but there are still vectors involved with the wheel relative to the water when it is moving on a boat. For the shallow angles of immersion we are considering it is not too bad though. It would allow reasonable prediction of drag coefficients for different shaped blades. Actual rpm and power input would not be very meaningful but they can be determined more accurately from the data. You would only turn the wheel at slip velocity not the full design rpm. So say 20% of the design maximum velocity.


    Anything to do with a foil is a lot more complex in the static state. It is not completely wasted because you can do estimates for the thrust it should achieve in the static condition. It also lets you sort out the cam control in real load application.

    For your spiral blades you can see what I mean for aeration.

    The prop I am talking about is simply a vertical axis turbine set on its side. very similar to the Voith prop. There is a simulation of that prop on the page I linked to. It has the standard controls and you can see the way the foils are controlled to give the thrust. Basically a wide shallow prop.

    To understand the curve it is best to do a few diagrams showing blades spinning and water going by. You need to show the vectors and do the vector sum to get the angle of the blade. If you have not got it by my tomorrow I will do some diagrams. It will be much easier if you have a look at the Voith simulation. It is quite instructive.

    Rick W
     
  3. Guest625101138

    Guest625101138 Previous Member

    So lets say the test unit operates at 20rpm.

    A motor able to produce 100W and geared at maximum for 20rpm will be more than enough.

    The force you are interested in is no more than 100N. That is around 20lbf.

    It will be a good unit to test different blades. There will be differences on a boat but it will not be too dramatic.

    What you have to realise is that you are primarily determining the drag coefficients of different blades for the paddlewheels. You might want to have some way of measuring vertical forces as well or at least make observations concerning them. Just videoing tests can be very instructive.

    All the other types of concepts are more to get mechanisms that work and some static load conditions. The Wide/Shallow prop should be able to generate very high thrust at low speed and low power because it works on a large area.

    Most of the stuff I work on I do scale testing and then concept testing at a larger scale so having a means to do this is very useful. I used to use the bathtub for preliminary scale testing but that is very water wasteful and not a good thing in our water poor country.

    Rick W.
     
  4. BG_Geno
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    BG_Geno Senior Member

    Rick--

    I can't get the simulation to play on their site for some reason.

    Maybe the scale idea isn't worth it then. I have some pond master pumps that move a good deal of water that could reproduce a flow but I imagine the tank would have to be pretty long.

    It just seemed like a good way to get a database going and answer questions like cupped or bowl, pointed blades, angled, what angle etc.

    As for the data you provided for a motor...those values/terms are not something they list on most electric motors. What I was hoping for was a rating or size or w/e that is common on motors.

    If it doesn't provide accurate data though I guess we are back to a build it on the boat approach.
     
  5. clmanges
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    clmanges Senior Member

    BG,
    Motor data, as printed on the nameplate, may be insufficient and/or insufficiently accurate, but any motor can be checked; there are labs that do this work with calibrated instruments, prony brakes, etc. I don't know the cost of such testing. It may be possible to purchase a motor that is specially made and calibrated for scientific work. I've never actually heard of such a thing, but it seems logical to expect -- price is bound to be high if they do exist.

    Quarter-scale testing seems pretty reasonable to me, but getting dynamic flow conditions complicates the test tank -- as it needs to be much longer. Look up wind tunnel testing; university labs sometimes build their own. Construction is simple, but includes things like flow straighteners. Water testing is more involved than air. I think there is a description of one of the setups in one of Jones' papers; if not, just start following links and references from there and you'll see one soon enough. You only need the clear viewing windows in a small portion of it where the test object is. You could also include a dye-stream injector quite easily.

    As much as I'd be honored to have something named after me, I couldn't say that it's very appropriate; after all, I don't know the math or much of the physics, and I haven't even actually built anything like this yet. Thanks, though. Keep looking into it; you've got a good start.

    What really shocks me is that we've suddenly outrun Rick's ability to provide quick answers! Give him a few hours or so, though . . . :D
     
  6. BG_Geno
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    BG_Geno Senior Member

    He did answer lol. You must have cross posted.

    As for a motor, I was hoping to use a stepper, like a Nema 8 or maybe Nema 11 because I could hook it up to a controller and then use my PC to set very precise output. Those steppers have something like 1.8 degree steps and you can control the pulse length between steps for nearly infinite output control. Great torque too.

    Like these:

    http://www.anaheimautomation.com/hightorquesteppermotors.htm

    i already have the controller and the power supply. Software too. You could even simulate different loading conditions.

    Rick said it wouldn't be totally worthless, but not an overly accurate method either. The up side would have been being able to build a 1/4 scale wheel in 2-3 hours and for 5-10 bucks. If it's not what you need though, cheap and easy isn't a bargain ;)
     
  7. clmanges
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    clmanges Senior Member

    Well, I was just about to say that you could use any old motor; just hook a watt-meter to it and measure the load, but it looks like you've already got better stuff.
    I still think it's a good idea; some information is better than none, and can point the direction for more in-depth testing -- of course, that means a full-scale test tank for the more promising possiblities . . . you might wind up becoming your own research facility!
     
  8. BG_Geno
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    BG_Geno Senior Member

    Well, if nothing else...weeding out the misses lol.
     
  9. alexlebrit
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    alexlebrit Senior Member

    Rick, I'm having a hugely difficult time picturing what you're talking about, but the nearest I can get is some kind of foiled horizontal corkscrew? Is that it? Is it vaguely like an Archimedes pump but foiled?

    And has anyone contemplated a good old fashioned archimedes pump at all?
     
  10. clmanges
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    clmanges Senior Member

    Alex, it's all there on the Voith site.

    BG, it's too bad you can't get the Voith sim to work for you, it's fun. Odd thing; the rotational speed control doesn't seem to do much.

    The mechanism they use is more complicated than you'd need for a paddlewheel configuration, since you could eliminate the elements needed for "steering." It's all beyond me, so far, though, so I don't know just how it would be set up. Looks very promising, though.
     
  11. BG_Geno
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    BG_Geno Senior Member

    I got the site to work rick...I have to say, I am not sure why their airfoil works vertically, but the helix one wouldn't horizontally?

    If I were to take a cross section of a blade every 60 degrees say on the helix...it looks to be in about the same position as theirs pretty much. The spiral I designed twists as well as the helix in case that was not apparent in the drawings...they are small and lack a lot of detail at that size.

    I understand that they don't have a hinge point, but it "seems" like the radial "climb" does similar. If you were to just see the airfoil in a cross sectional slice as it climbed, and froze it every inch of progression radially AND with the twist...it really does mimic their feathering vertical prop...not as dramatically when they are really cranking over of course, but their mid range.

    Anyway...check your mail in about 1.5 hours. Your package will be done then.
     
  12. BG_Geno
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    BG_Geno Senior Member

    Curtis...It may be simpler without the steering but its still going to be just as hard and just as heavy as a feathering paddle wheel...and that's worked so well for us so far lol. They have a cam like action going on too.
     
  13. clmanges
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    clmanges Senior Member

    Yeah, as near as I can tell, it's ALL cam action. The mechanism would require a good deal of precision, but I'm thinking that for an HPB, it could be made of GRP instead of metal. It only needs the cams at the drive end, the non-driven end needs only a free-turning disk with a simple bearing for each blade.
     
  14. beppe
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    beppe Junior Member

    invention vs. innovation

    No doubt, BG, no doubt. I'm looking in amazement at this collective development propelled by collective intelligence going on in your thread, possibly leading to the 'invention' of your boat in the form of a prototype.
    The Open Waterbike project is not about invention, but innovation. It's the successive step, in short the successfull diffusion of invention. We are working on different links of the same concept. Invention is the fuel of innovation, but invention alone is not enough. Many a great PPB 'inventions' failed as innovations, from early attempts in the 19th century to the Sea Saber back in the seventies to the Wavebike. There are reasons to believe that The Open Waterbike project could be a new approach to PPBs innovation. Excuse me for this detour in your thread, prompted by your comment...
    Believe it or not, i'm proud and honoured to be a member of Human Powered Vehicle Association, and to give my humble contribution to its ideals and dreams; even you don't believe in The Open Waterbike concept please give it a chance: we are on the same side.
    Beppe
     

  15. BG_Geno
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    BG_Geno Senior Member

    I don't discount your approach Beppe. Just not a good fit for me on tis particular boat. Or maybe this boat isn't a good fit as its a paddle wheel etc.

    We need as many irons in the fire as we can get =).
     
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