Need your thoughts- Hobie Trifoiler/Dared Kiteboat/Self Design Frankenstien

Discussion in 'Boat Design' started by LeeDesign, Jul 11, 2018.

  1. MurphyLaw
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    MurphyLaw Senior Member

    Get hold of a Raspberry computer Raspberry Pi 3 Model B - Raspberry Pi https://www.raspberrypi.org/products/raspberry-pi-3-model-b/

    Check the projects they have on the Pi web site.

    Making an Autonomous Boat Using a Raspberry Pi (WiP) http://www.instructables.com/id/Making-an-autonomous-boat-with-a-Raspberry-Pi-a-/

    There is a module for measuring distance that you can plug in and there is lots of modules for controlling servos/motors/anything.

    All these modules only cost $50 dollars max and the computer is only a hundred dollars, you can also get waterproof casings etc.

    You could measure distance to the water just using infra red light, the more light reflected back the closer you are to the surface. You could use radio waves and capcitance a combination of them all would be very reliable.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    ================================
    Other than the AC 50 cats the best example of successful use of electronics in sailing (aside from many sailboats for disabled sailors) is the Super Foiler Trimaran:
    Super Foiler Grand Prix 2018-starts February https://www.boatdesign.net/threads/super-foiler-grand-prix-2018-starts-february.59736/ So far as I know, though, no electronic altitude control for small boats has worked-mainly due to spray interference......
     
  3. MurphyLaw
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    MurphyLaw Senior Member

    A good one to avoid interference, is to suspend a ping pong ball in a tube that is sealed from light to the side of the boat, when the hull rides high the ping pong ball sinks to the bottom of the tube, when it rides low the ping pong ball goes to the top of the tube. At the top of the tube you mount a LED and a receiver, when the ball is at the top it will reflect a lot of light, when it is at the bottom it wont reflect as much. As it uses light the response time will be rapid.

    Edit; you could have a pipe/hole running the length of the core of the foil, with a small floating ball in it which would be best. A foam ball covered in metallic silver paint, when the foil is at it's highest position the ball will be at the very top, making all the light reflect back, as the foil rises the ball will start to drop from this position and less light will be reflected back. You can encase the LED and receiver in clear epoxy resin and a shiny silver ball is a shiny silver ball, you would make the tolerances between the ball and the tube very large so it never gets stuck, you are not trying to seal water in or anything. This is the most bomb proof method I can think of, as it will be immune to sea conditions, because you are effectively measuring the pressure where the hole meets the sea at the bottom of the foil. Unless the very bottom of the foil leaves the water the reading will be accurate and not effected by what it happening on the surface. When the foil leaves the water the ball will be at the very bottom of the foil and stay there till the foil goes back in the water. The readings to the computer will decrease and decrease then stay at a max decreased value, then increase again until the foil is at it's correct position. You can accurately tell, when the foil is in the water, when it is not and when it is in the correct position. It wont be effected by dirt as it will quickly become obvious which is the maxed out reading and which is the minimum reading, so it would be simple to auto calibrate on the fly, if you sailed into muddy waters it would not effect the system. To service the system just clear pipe with hosepipe and water and wipe sensor head. Use a RED LED so the system is easy to check, look in hole, can you see red light?
     
    Last edited: Jul 17, 2018
  4. MurphyLaw
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    MurphyLaw Senior Member

    In fact this is the method I am going to use with mine, I am going to try with a bucket of water and a piece of PVC pipe and report back
     
  5. LeeDesign
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    LeeDesign Junior Member

    That seems fairly reasonable to me. Though if I were to do it for my project I would need fairly detailed step by step instructions to get it done. Im more mechanical then electrical.
     
  6. MurphyLaw
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    MurphyLaw Senior Member

    Something like this, the top of the tube must be ventilated to the atmosphere.

    [​IMG]

    If you use 2 pipes in each foil then by comparing the 2 readings you could even calculate pitch
     
  7. MurphyLaw
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    MurphyLaw Senior Member

    I really need to get going on my project, where about are you on yours, I have all the computer stuff and I just need a weight of craft to calculate the torque required for the servos, stepper motors are OK for light model stuff, but I doubt you will have enough torque for a human craft. The best best is servo motors because if it fails it will just stop moving and not suddenly move to a neutral position.

    You need to find out the torque required for the servo motors before going further, have you found this out ?

    Check this web site out they sell stepper motors and gearboxes etc with different torques that you can connect up to a Pi.

    Motors & Servos https://www.pishop.co.za/store/motors

    A motor to a gearbox is the best option IMO, the changes to the foil need to be 1. more lift 2. less lift and not a discrete position. that way you dont need to worry about loads on the craft.

    If you can find out what the toque requirements will be to move the foil then I can order some servos and start testing this end, or you can order a Pi computer and the same servos and work in parallel.

    That same company sells a positional sensor that can sense the pitch and roll of the boat, same as what they use for drones.

    GY-BNO055 9DOF 9-axis BNO055 Sensor https://www.pishop.co.za/store/sensors/gy-bno055-9dof-9-axis-bno055-sensor

    I am going to use one of those Pi computers connected to the inertia/position sensor and then a height above the water sensor to control the foils, I will be able to tell the exact position the boat is in, it's speed and acceleration, it's direction and the height above water.

    Other work to be done would be to experiment with tubes and balls in a pipe, the ball needs enough buoyancy so it doesn't bounce around on the surface, too light and too buoyant and it will jump up and down, too heavy or not enough buoyant enough and it will be too slow to react. How much weight it has will be like a shock absorber to sudden changes.

    The max size of the pipe will probably be 10mm less than the thickness of the foil, you do not want the hole to compromise the strength of the foil. Maybe start off with a 12mm pipe and a 10mm ball inside.

    Go make such a pipe and ball out of clear plastic and take to a swimming pool or bath and see what happens when you plunge it in and out of the water, what effect does the size of the ball have on how it behaves? maybe if you make it a tight fit, it will react more smoothly as you have made a shock absorber of the air passing by. I am certain there will be a pipe and ball size etc that will give you nice smooth readings.
     
    Last edited: Jul 17, 2018
  8. Doug Lord
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    Doug Lord Flight Ready

    I would think two pipes per foil in the water would be waaay more drag than a simple wand.......
     
  9. MurphyLaw
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    MurphyLaw Senior Member

    No there are no pipes in the water, the pipe is inside the keel, less drag than a wand, you put the pipes inside the keel when you make them, you need to use T-foils. the end of the pipe/hole is at the bottom of the T-foil keel. See the diagram I posted, that is looking side on at a T-foil.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    What would prevent the water in the pipes from being sucked out at speed?
     
  11. LeeDesign
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    LeeDesign Junior Member

    2 things I see so far that need to be addressed: with the sensor tube inside the mast the foil will be reacting to whatever conditions are already at the mast. This is opposed to a sensor that is in front of the mast, preparing the attitude of the boat to whats coming. (Imagine coming into or off of a wave)

    Second would be the point that Doug brings up. A venturi pump operates by using a high velocity stream of fluid (usually air or water) to accelerate a stationary fluid, creating a pumping effect. In this case the high velocity fluid would be the water moving past the boat, while the stationary fluid would be the water inside the tube. I see no way to keep it from being sucked out.


    Anyways, as far as your question goes as to where my project lays: It is still vaporware, just a model. However this week I am purchasing some materials to start construction. Its just 4'x8' by 1.5" foam, but its a start that doesn't cost much in the way of money. However I foresee construction going pretty quick.
     
  12. TrevorJack
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    TrevorJack New Member

    I've been using Glidefree foils (www.glidefree.com.au) on a Nacra 5.8 kite boat for a few years. Here's some recent video: . The Glidefree foils are symmetric (NACA 64012, I think. Perhaps Naca 64010). The full foil is rotated to manage AoA. AoA range is from about 2┬░ to 12┬░. Control is with a push rod which is not fixed to the lifting foil - so the foil can only lift upwards, it cannot lift downwards (as the "push rod" can't pull the foil up).

    Although they work reasonably well and are an easy retrofit option, that the heave sensor is at the foil is quite a problem in any chop. Not surprisingly, we climb over waves then, with 3m of bow/hull hanging over the wave in front of the main foils, end up diving into the troughs. I'll go back and read Doug's references to bow v near CoM sensing, but my understanding is that having the sensor as far forward as possible would be much better.

    Although I could install wands and the associated linkages, for a variety of reasons I'd prefer to use an electro mechanical system with bow sensors.
    LeeDesign, if you have very little boat in front of the main foils, sensing at those main foils may be OK. But from your comments, I'd do a lot more reading about pitch stability before finalising the design. Pitch stability requires the right relationship between position of CoM and relative lift from the main (forward) foils and elevator.

    If you were to use a sensor at the main foils, you could try a cheap laser range finder reflecting off the main foil (it won't reflect of the water surface). You would need the control algorithm to calculate height allowing for the refractive index of the water. That is, measured distance (without altering the range finder) would be greater when the boat was flying lower (or in Archimidean mode) as light speed in the water would be less than that in air (as assumed by the range finder).

    I'm interested in any suggestions for sensing height without using anything (eg the main foil) in the water. For example, I'd like to leave a through hull sounder installed in the hull. For non-foiling use it would not be in the way (you wouldn't know it was there). When foiling, I'd connect a battery and have a radio link to the actuator. This project (Flying over the water with ToughSonic®14 Ultrasonic Sensors https://senix.com/toughsonic14-ultrasonic-sensors-control-hydrofoiling/) in the Netherlands uses what looks like a good commercial sensor - but that's a little more expensive than I'd like to be forking out.
     
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  13. Doug Lord
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    Doug Lord Flight Ready

    Great post, Jack! I included comments from Tom Speer(pro forward wands) and Ron Price( pro-midship wands). In addition, almost every Moth is using forward mounted wands and the original Hobie Trifoiler used forward mounted "feelers" with an all moving board. In addition to Ron Price, designer of the Whisper, Dr. Sam Bradfield used mid-ship wands on his Rave, SKAT and Osprey. One of the keys to Bradfields and Prices system is the ability for the foils to develop downforce so that dual independent wands can develop RM for the boat. The key to midship wands is that the wand hits the water at the fore and aft CG of the boat and pitch control is 100% from the rudder T-foil. I find your description of the Glide Free system very interesting- especially the part about not developing downforce. Seems like that could be more of a cause of the behavior that you describe than the midship position?
    Anyway, thanks for the information on sensors-I've been wanting to look into that.
     
    Last edited: Jul 19, 2018
  14. LeeDesign
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    LeeDesign Junior Member

    Okay, here we go again.

    Current revision, shown without foils/linkages/wands (too tired right now).
    Free board is purposely very low, about 2 inches below the pilots butt, hopefully allowing the pilot to board a bit easier from the water while attached to his kite. This is also the reason for a single arm to each outrigger. Main hull is 9ft long, beam ditto, bouncy supplied with the water line 2 inches below the pilot is 190 lbs. In the side view, imagine the water line at the base of the pontoon. The model pilots positioning is a bit wonky, never mind that.

    Mini Tri.png mini tri side.png mini tri front.png

    Thoughts, everyone?
     

  15. Doug Lord
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    Doug Lord Flight Ready

    Assuming you have the CG correct(80% of load on the front foils, 20% on rudder foil-kite load led to position of CG) it is much better! Good Luck....
     
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