Electronic Foil Control

[Chris Ostlind]

I know that more than a few of you read the postings over at Sailing Anarchy regarding the world of all things foiling. But for those of you who do not, a fairly huge potential development was revealed today in the form of an electronic foil control system that is being developed by Clive Everest.

The SA threads from which the revelation took form are here:
http://tinyurl.com/4lzaso
http://tinyurl.com/4zzd3h
(these should work, but I'll check them anyway)

This thread is one of Doug Lord's topics regarding his penchant for midship wands. Other than the very few prototype craft, where one of these midship systems is actually installed, the foiling world has not adopted the ideology behind the system's use and instead, continues to use the bow mounted wand setup that you see on virtually all the Moths with foils.

Over the course of that thread, the idea was put forth as to the credibility of an electronic foil control system with lots of back and forth discussion related to the potential. This resulted, today, with the introduction by Clive Everest, of his developmental work in this very area of viable electronic control for foil surfaces while sailing.

The very end of the link shown above will point you to the work done by Clive in this regard, complete with the all-important photos to substantiate his claims. An open invitation to Clive has been given and I hope he makes a visit here to discuss his work in progress.

I'm not going to poach Clive's postings and images from SA in a wholesale fashion. Instead, I would prefer if he would join the group here and speak for himself as to his work, his purpose and where will he go from here.

Chris Ostlind
Lunada Design
www.lunadadesign.com

[tspeer]

Besides the wand, Clive includes an accelerometer and a rate gyro in his sensor suite. These additional sensors are probably the biggest benefit to electronic control over mechanical feedback.

The craft should fly over small waves without reacting to them, and only follow long wavelengths that have amplitudes higher than the flying height. So for high frequencies, it should fly level with regard to inertial space, and the accelerometer and rate gyro allow it to do this. For long wavelengths, it can respond to the wand, and doing this through pitch control is no problem if the long wave periods are slow enough.

One reason for using the front foil for active heave control is it effectively gives the front foil more heave stiffness than the rear foil, which provides stable pitch-heave coupling. But the dynamics of the craft can be augmented by the inertial sensors so that it can still be stable when controlled by the stern foil.

[RHough]

Originally Posted by tspeer

Besides the wand, Clive includes an accelerometer and a rate gyro in his sensor suite. These additional sensors are probably the biggest benefit to electronic control over mechanical feedback.

The craft should fly over small waves without reacting to them, and only follow long wavelengths that have amplitudes higher than the flying height. So for high frequencies, it should fly level with regard to inertial space, and the accelerometer and rate gyro allow it to do this. For long wavelengths, it can respond to the wand, and doing this through pitch control is no problem if the long wave periods are slow enough.

One reason for using the front foil for active heave control is it effectively gives the front foil more heave stiffness than the rear foil, which provides stable pitch-heave coupling. But the dynamics of the craft can be augmented by the inertial sensors so that it can still be stable when controlled by the stern foil.

Thanks Tom, that completes the picture for me. A rule 52 not a sailboat anymore solution.

[Fanie]

Chris, your link is not working.

[foilman24]

so here is the skinny on this:

(posted by Clive Everest on SA) I have a foiler that is flying under full electronic control.
The boat is considerably bigger than a Moth.
At 195 lbs I am significantly heavier than a sensible weight for a Moth, though I did sail Moths competitively some 20 years ago.
The boat is 4.5m long 3.2m wing span and 12.5m2 sail area, It is about 55kg fully rigged. It has similar sail carrying ability and sail area to weight to a Moth.
The boat was flying last year under mechanical control how ever there are inherent limitations in the standard control system that the Moth sailors hide with a lot of skill and practice.
It had always been my plan to develop electronic control for this boat.
The boat now uses an RS600FF main foil with the flap glued solid.
Control is through a smaller balanced rudder foil using a Hitec HRS5995TG RC servo.
I have now had 5 or 6 hours of electronically controlled flight with no servo failures, once I had worked out how to stop water ingress.
Initial attempts to put a second servo to control the main foil flap did result in failure of the servo under static load.
The core elements of the control unit are a dsPIC30F6012A processor, ADXRS300 solid state gyro, LIS2L02AL solid state accelerometer for DC pitch measurement. The control unit has a 2x20 character display for diagnostics, a keypad that allows me to adjust key control parameters whilst afloat, and 2M of NVRAM for data logging.
Height is still measured with a wand that is connected to a POT.
The unit is powered by two 7.4V 4.2AH Li Ion Batteries. I think that I seriously over estimated the battery requirement as it is still virtually fully charged after 2 hours afloat.
The entire electronics package including batteries and servo weights 900g. It could be less with reduced battery and no display or keypad.
The system is still in early stages of development, though last weekend I did line up against Si Payne, and whilst he was faster upwind and down the difference was not that significant.When I had a mechanical linkage (when the pic was taken) the twin dagger boards allowed a single higher aspect main foil to be used without the weekness of the T joint. It also allowed thewhole foil to articulate and be controlled by the wand and not just the trailing edge flap giving greater control authority but more drag around the joints.
Also any control system that exclusively controls the main foil cannot provide an effective reactive torque to gusts on a high rig. Hence the wild course sailed by Moths downwind in windy weather.
I now have a fixed main T foil and a controlled foil on the rudder.
Controlling through the rudder foil does generate new problems due to the extra lag in the control loop. It is akin to reversing a trailer rather than pulling it.

[Chris Ostlind]

The links have been fixed in the first post.

Thanks for the heads-up Fanie

Chris

[waynemarlow]

There seems much debate on the need for some sort of foil pitch adjustment on the front T foil and the need for also a control on the rear foil, that aren't we simply creating problems for ourselves. From where I sit once the hull is airborne you don't want the front foil to be doing anything apart from being as neutral ( horizontally ) as possible, it is irrelavent if the hull goes up and down height wise in respect to the water as it has no contact with the water with the foil taking all the loading. A 1 metre long foil in a technical sense should be able to deal with a say 900mm swell. Anyway over that sort of swell height you simply are not going to be able to practically sail ( try taking a ride in a rib at 20knots in a 1 metre swell ).

Having watched a couple of Moths at our club foiling they are creating so much lift that the foil is being almost exposed rather than where I would have though with just enough lift to keep the hull out.