Electronic Foil Control Systems.

[BalticBandit]

My next step is to use a vertical accelerometer to detect short term height changes and the wand to provide long term reference.This is not as easy as it sounds. changes in pitch, heel forward and lateral acceleration affect the vertical acceleration reading. The double integration rapidly generates significant errors.

have you considered looking at the various 3D "air mouse" products? They have done much of the work disambiguating this into inputs that convert to USB data.

Will the LEDs be confused by water on the lens?

I honestly don't know. I suspect it would depend on the way the lens system is designed.

My preferred method of non contact height measurement is to look at the capacitance between an area on the bottom of the hull and the water.
Clive.

DAMN that's clever! I really really like that.

 

[Doug Lord]

Clive ,if you haven't already you might be interested in looking at this:

United States Patent 3704442

"Abstract:

A method for detecting the relative position of a gaseous-liquid interface with respect to a datum point and an apparatus embodying the same for use in hydrofoil height sensors. A transmitter situated on the watercraft's hull directs an ultrasonic signal at the water surface. A portion of that signal is transmitted through the surface and refracted thereby to an ultrasonic receiver preferably situated on the hydrofoil. Evaluation of the transmission time of the ultrasonic signal from the transmitter to the receiver yields significant information concerning the relative position of the water surface with respect to either the hull or the hydrofoil. Factors for successful implementation of this technique are discussed in detail, and reference is made to a specific embodiment of a detector for transmission times. "

 

[Christian]

My next step is to use a vertical accelerometer to detect short term height changes and the wand to provide long term reference.This is not as easy as it sounds. changes in pitch, heel forward and lateral acceleration affect the vertical acceleration reading. The double integration rapidly generates significant errors.

Will the LEDs be confused by water on the lens?

My preferred method of non contact height measurement is to look at the capacitance between an area on the bottom of the hull and the water.

 

Clive.

Sounds like worth while checking out. You might find, though, that the capacitance is going to be highly affected by the relative humidity and the amount of spray in the air between hull and water - and in the case of spray it will probably also be affected by the salinity of the spray. It may be a minor influence - I don't know.

 

[the_skiff_devil]

Couldn't you mount a little generator between the foils like the 747s have for when they lose power, because when your not moving your not going to need much electricity, and its not stored power because your using wind power to generate it, and your wont have to lugg one of those heavy batteries around. It would have to be dectachable so that you wouldn't need a massive trolley. Also you wouldn't be limited be battery life, in case you have to launch at like 8am, then get postponed for like 8 hours. See rendering.

Nice rendering kid

Good enough an idea kid but a small masthead wind generator or a solar panel would be better simply because it's out of the way of the free flow around the foils... rudder vent is bad enough without a prop out in front of it curling the flow up before it hits the rudder!

Re: Bungee storing energy... well, in that case every shock-cord take up on every dinghy on earth causes them to fail rule 52 since they use the stored energy of the shock-cord to clean up the boat which assists in reducing the cleanup work the skipper has to do, allowing the skipper to concentrate on driving the boat harder and improving speed. I won't even start on spring-loaded cam cleats... Yeah, we'll let those slip.

Chris Miller had a good idea with the resistance of a metal strip being used to detect the water level - I think that if a metal strip were used to sense for an average flying height and a bow-mounted wand to detect waves were combined it would give a pretty reasonable pitch controlling system... but I'm not sure if it'd be enough to overcome the natural lag from the foils. Basically, it'd need to be fast enough to predict a wave coming or leaving by a couple of tenths of a second abd have the main foil adjusted to suit before the wave encounters the foil... while electronics are good enough to do that I don't think there are lightweight servos that are quite up to the job of constantly moving the flap for a long period of time.

 

[Sailingkid]

Thanks! Since you liked them so much :lol: , heres another one using ur idea, and my idea, using the sail as a solar panel.

 

[BalticBandit]

Clive ,if you haven't already you might be interested in looking at this:
United States Patent 3704442

"Abstract:

A method for detecting the relative position of a gaseous-liquid interface with respect to a datum point and an apparatus embodying the same for use in hydrofoil height sensors. A transmitter situated on the watercraft's hull directs an ultrasonic signal at the water surface. A portion of that signal is transmitted through the surface and refracted thereby to an ultrasonic receiver preferably situated on the hydrofoil. Evaluation of the transmission time of the ultrasonic signal from the transmitter to the receiver yields significant information concerning the relative position of the water surface with respect to either the hull or the hydrofoil. Factors for successful implementation of this technique are discussed in detail, and reference is made to a specific embodiment of a detector for transmission times. "

Not a valid patent as it fails the "prior art" test. I read your patents Doug, you fluffed the "prior art" part and therefore jeopardized the validity of the patents themselves. I assume that you wrote them yourself without consulting a real patent atty. Too bad. A good one might have made you some money.

Couldn't you mount a little generator between the foils like the 747s have for when they lose power, because when your not moving your not going to need much electricity

This would generate drag and turbulence. So that means you would have to tow it aft of the stern to preclude it being a ventilation inducer (remember just the wand itself can induce ventilation) And it generates a fair amount of drag. Lastly in a crash, the last thing I want is a spinning prop at the end of a fairly heavy metal can (the generator) whiplashing at me from behind the boat.

Note the Solar panel sail (setting aside the weight issues), is not "action of the wind and water" As for shock cords. I suspect that if you had bungees attached to the boom that allowed you to pump the main based on stored energy, you would fail 52, though the arguement could be made that the energy put into the bungee comes from the "natural action of the wind and water". the gotcha on electronic systems is that the energy is coming from a pregenerated form (except for SailingKids taffrail generator idea)

Nice thinking though - out of the box.

I suspect it would be simpler to hvae a separate "EC" class at big regattaes with tinkerers sailing the ECs starting with everyone else, but getting scored separately. You'd want to start them with everyone else just so that you can start to get a feel for how they are doing compared to manual control boats.

 

[Sailingkid]

Don't finns have thick bungee going from the bow to the end of the boom then back up to the mast then back to the bow to help pull the boom out to assist pumping?

 

[Doug Lord]

Clive, I have a couple of questions: if I understand your system correctly your wand operates a pot sending a signal to your electronics. Does that mean that the sometimes rapid wand movement (that on a "normal" foiler would also move the flap up and down rapidly) is not transmitted to the rudder foil flap? In other words the rudder foil flap would not move as rapidly as the wand-is that correct?

Do you think a future version of your system would benefit from simultaneous control of both the main foil and rudder foil?

 

[Doug Lord]

For those interested in Clive Everest's electronic foil control system here is some of the amazing background of the man himself by Andy Rice in 2004:

=====================

Clive Everest has also been inspired to draw the lines for his own foiling machine. Best known as the designer of successful singlehanded classes, the RS600 trapeze boat and the RS300 hiking dinghy, Everest is an unreformed speed junkie. He has raced International 14s, 18-foot Skiffs and most recently an A-Class catamaran. He also has a history in Moths, including designing the world championship-winning Moth of the early 90s and finishing second in his own right as a sailor. He was also part of a pioneering group who experimented with foiling over a decade ago. “I was involved with Moths when we were experimenting with a tri-foil arrangement, but then the class banned it,” he says. “These days at 13 stone I’m too heavy to campaign a Moth competitively; you’ve got to be about 10 stone and I think the weights might come down even further with the foils. But I was totally inspired by what Rohan Veal was doing so I decided to design my own boat, with no rules or restrictions to worry about.”

His own RS300 design, itself a derivative of the Moth, has proven fast and easily driven in light winds so Everest took this as the basis of his new foiler. “The only time the hull’s going to be in the water is in light winds, so the RS300 seemed like a good place to start.” Because Everest only expects to be sitting on the water in conditions of 7 knots or less, he has had the top 150mm of freeboard chopped off the RS300 hull to save weight, and has commissioned Richard Woof of RMW Marine boatbuilders to construct the hull of carbon.

To this hull Everest is attaching carbon trapezing racks for added leverage. The rudder and rudder box are standard 49er equipment, with the addition of a T-foil wing to the base of the rudder. The rig consists of a carbon mast and fully-battened Mylar sail. So far, the basic configuration differs very little from the Rohan Veal Moth, but where it differs is in Everest’s approach to the foil arrangement. “I have adopted a tri-foil arrangement similar to what you see on a commercial passenger-carrying hydrofoil ferry,” explains Everest. “We experimented with this set-up on the Moths 10 or 15 years ago but because the class banned it, Rohan has had to go for his more complex T-foil arrangement.”

Unlike the T-foil system, Everest’s tri-foil configuration has no moving parts and there is less tweaking and calibration involved as a result. The hull is supported on two carbon foils, one from each trapeze rack, angled at approximately 45 degrees underneath the centre of the hull, with the T-foil rudder providing a small element of lift at the transom. It will run closer to the surface and will provide a more stable ride than the high-flying Moth of Rohan Veal. It may look a little less spectacular but should prove equally fast, if not faster, with anticipated speeds of up to 25 knots. “I wanted something simple and maintenance free. I’ve got a young family and limited time to go sailing, so the tri-foil will just let me get on with the fun part,” explains Everest, who plans to club race his foiler during the summer in Chichester Harbour. “The aim is to give the fast twin-trapeze boats like the International 14s a good run for their money.”

Everest’s Achilles heel is going to be in the sub-foiling conditions when all that hydrofoil becomes added drag, but he has given himself a big rig and big foils to promote early foiling, at the expense of reduced top speed. And unlike the Moth, he has the added turbo of a small gennaker which he will hoist downwind in light to moderate conditions. “Because of the amount of apparent wind, the sail is very flat - more like a Code Zero than a gennaker. But once the wind is above a Force 3 to 4 I expect to be generating enough power around the course with just the mainsail.”

 

[Cheesy]

Hi Clive, if you don’t mind elaborating a bit more could you give us/me an idea of how you are using the gyro and accelerometer inputs.

On the height input a few years ago while I was at varsity there was a group developing thin film devices for measuring boundary layer thickness, it may be possible to use several devices like this on the foil strut to give incremental height steps, I’m guessing that by using the accelerometer and gyro you aren’t actually using the wand to control any pitching etc, just a heavily filtered input for the height control?

 

[clivee1]

The inputs to my electronics are the wand, A solid state gyro mounted in the pitch plane which measures the rate of pitch rotation, an accelerometer mounted in the pitch plane that will respond to changes in pitch and acceleration of the boat. This is used to provide a low frequency reference to the gyro. as it is safe to assume that the long term acceleration of the boat is zero, and a vertical accelerometer.

I have 2 nested control loops. I drive the rudder foil servo to try and achieve a target pitch based on the pitch measurement that comes from a hardware integration of the gyro out put and the pitch plane accelerometer, and the rate of change of pitch that comes directly from the gyro.

The target pitch is set by the height control loop as a function of the measured height from the wand and a software integration of the height.

I want to use the vertical accelerometer to measure the vertical velocity and acceleration to provide phase advance to the height control loop. I also want to double integrate the acceleration to generate a second height reading that will allow me to separate the vertical motion of the boat from the contours of the waves.

My initial attempts to do this have not worked as small changes in heel and pitch change the measured vertical acceleration and the double integration rapidly produces significant height errors. Whilst I can correct for the error due to pitch I need to measure heel to compensate for that, This is my next step.

Both control loops have non linear gain functions so that when running close to target setup they do not respond significantly to small deviations however the responce gets much more agressive if the boat is seriously out of shape.

Regarding the question as to whether a second servo on the main foil flap would be beneficial:

Undoubtedly the height control could be improved and in no way would it be diminished. However in the horizontal plane we do not need a rudder and a centreboard trim tab to steer our boats so why should we in the vertical plane.

Also it would duplicate a relatively expensive and vulnerable part of the system.

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.

I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

I must reiterate that I feel that I have made the first step and do not for one second want to think that I am any were near what will be achieved.

I liked the analogy of the Wright brothers 26S flight.

Clive.

 

[atypicalguy]

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

I must reiterate that I feel that I have made the first step and do not for one second want to think that I am any were near what will be achieved.

I liked the analogy of the Wright brothers 26S flight.

Clive.

The Wright Bros. patent was actually on a control system - many had flown before them, but no one had sustained it because they could not control the flight.

I have a similar speed-limited sensation on my moth, though I am not sure what the ultimate cause is. Getting rid of flaps is certainly a step in a good direction.

Pitching the rig seems a slow way to fly, but perhaps the impact is negligible at speed.

In terms of drag that second vertical strut must be adding significantly; surely with a bit more material in the foil this could be eliminated?

 

[SimonN]

Clive

Thanks for posting. As always, the stuff you do is very thought provoking!

For me, the biggest thing you raise is not actually the electronics but this

I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

While I might not be qualified, never mind more qualified, I would make the following observations. It has struck me that the top speed of Moths hasn't improved for the last (I think) 3 years. Some have put this down to inaccurate measring of that speed but if we look at the data and ignore the tails, I think that we do observe some sort of barrier. At the same time, the speed around the course has improved dramatically. I am prepared to accept that the textbooks are right, in no small part because those same text books are used to design large aicraft and they seem to work! Whether your theory is right s to what is acusing the problem I don't know, but I suspect that this is where the next big breakthrough will come from.

 

[JimC]

to help pull the boom out to assist pumping?

Mainly to avoid having to push the boom out by hand running square I believe.

 

[BalticBandit]

Undoubtedly the height control could be improved and in no way would it be diminished. However in the horizontal plane we do not need a rudder and a centreboard trim tab to steer our boats so why should we in the vertical plane.Also it would duplicate a relatively expensive and vulnerable part of the system.

I think the latter arguement is the stronger one. The horizontal plane analogy isn't as strong as in the horizontal plane we are primarily concerned with attack angle of the airfoil and are using the rudder to control AoA rather than trying to control lateral translation.

but the strongest arguement I think is

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

Seems to me then that if you were able to fly the whole foil (ala modern airplane Stabilizers) you would be able to have a clean structure AND have that control. But then you need more power, which argues for the approach you are using.

 

[BalticBandit]

Most importantly however: I found last year sailing with a mechanical system that I seemed to be hitting a hard wall regarding max speed. Contrary to all the text books the drag appears to be going up far faster than V^2.I have an unsubstantiated theory that around 18Kts we are starting to see true cavitation around unfair parts of the structure and that the size of the cavitation bubbles grows rapidly causing the rapid increase in drag.

I hope someone more qualified will comment.

By fixing the main foil flap and removing the push rod cut out I have the opportunity to make a significantly cleaner structure.

I must reiterate that I feel that I have made the first step and do not for one second want to think that I am any were near what will be achieved.

I liked the analogy of the Wright brothers 26S flight.

Clive.

Over in Sailing Anarchy forum someone just posted the announcement of a new breakthrough in fluid dynamics modelling

http://www.dailytech.com/article.aspx?newsid=13067 is the link to the story behind it. Potentially has dramatic impacts on foiling blades

 

[Sailingkid]

Mainly to avoid having to push the boom out by hand running square I believe.

Cool now i know why they have it!

 

[clivee1]

I have managed to get afloat again after a month of poor weather and other commitments.

Key change this time has been the addition of a data logging capability and the ability to send the servo to max to generate a disturbance to evaluate the control.

This data should allow me to now start optimizing the control.

First impressions are that the servo is responding far too much to chop but not actually managing to control the height that well.

I need to separate chop from height changes without adding a lag to the control loop.

The GPS logged 10 NM of sailing during an hour afloat with top speed of 17.1kts I did not push the speed as the control looked like it would become unstable at higher speeds.

 

[Cheesy]

would it be possible (or even feasable) to use a double differential of the vertical acceleration to calculate the change in height and then use the wand input peiodicly to define a start value for of the system ?

alternativly would a low pass filter be enough to eliminate most of the problem?

 

[clivee1]

I think that a double integration of the vertical acceleration with a slow (~5 seconds) convergence to the wand reading is what I will try next.

I think that simple filtering of the wand will reduce the control potential.

My previous experiments with a vertical accelerometer showed that I will need to compensate for pitch and heel.

My other thoughts were to use pitch and speed measurements to predict the rate of rise and an estimated height and steer this to converge with the actual wand reading.