Vertically mounted solar panel

[andy]

Hi all, I am solving the last issue with my current boat design.

The question is how to deliver power to the actuator that is mounted on a free-rotating wingsail. I have three options:

1) Use a flexible cable inside the mast. I must take care not to overtwist the cable. A hall sensor would count the number of rotations of the wingsail. If the cable is twisted let's say 5 x 360 degrees, the algorithm would turn the boat 5 times until the cable is straight.

Pros: It's the easiest solution.

Cons: If the boat becomes uncontrollable during a storm, the cable may accidentally overtwist and break.

2) Use a slip ring

Pros: It solves the above problem with the flexible cable.

Cons: The slip ring must be IP68 waterproof and very reliable at the same time, which looks like a point of failure. The rotary seal would also add resistance (the wingsail is free-rotating and it must always turn in wind direction). It's likely that the rotary seal will fail after billions of small oscillations.

3) Use a separate power source inside the wingsail and control the actuator wirelessly – this is what I like the most. I realized that the actuator + electronics + wireless receiver inside the wingsail would consume max. 10mA on average, so I can use a lightweight battery. What I can't figure out is whether I can get enough power from a vertically mounted solar panel. The solar panel must be lightweight, and therefore as small as possible. However, I need a guaranteed uptime when the main battery has enough power for steering. Do you have any idea how much power I would get when compared to a horizontally mounted solar panel?

Pros: It solves all the problems.

Cons: It's complex, the wingsail becomes heavy, waterproof hatch for replacing the battery (yeah, "dangerous goods"), unknown solar power requirements

[Roger Llewellyn]

HI All,

 

Assuming you can make a sail light enough (then strong enough), how about putting a very small battery at the base and once a day (or when the battery is fully charged) chop the dc into an inverter and transfer the power by induction? Although there are losses in this? but it would be waterproof.

 

 

 

Just a thought?

Roger

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[andy]

I have been thinking about transferring power by induction, but then I have the same weight and complexity inside the wingsail as with the solar panels.

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[Dicks GMail]

A fourth option would be to mount the actuator  in the hull and link it to the control tab on the sail mechanically.  In a similar way that helicopters transfer control to the rotor blades via a swashplate. This could be installed at the base of the mast and transfer the actuator movement by push rod or Bowden cable to the control tab. I imagine the force required to operate the control tab are relatively small so it could be a single rod push action with a spring return. Or a double cable push pull as you did for you rudder last time I believe.

So it has some similarity to a slip ring, ie sliding surfaces or a simple thrust bearing, eg two disc with a captive marble between them, but your just transferring a low pressure push not establishing an electrical connection.  However as it would not involve any electrical connection more robust materials could be used.

This provides the benefit of all the electronics being within the hull and no complication of separate batteries, induction charging, electrical cables, etc., crossing the rotating ‘threshold’.

BTW what CAD system have you found useful for creating your drawing, is there a good cheap one around.

Cheers, Dick.

Sent from my iPhone

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[andy]

That's a really interesting idea. I am not sure I can design such a reliable mechanism, but I will think about it.  The force that controls the tail is relatively small, but in bad weather, the whole structure will be attacked by water.

Another issue may be the not-so-obvious turning effect of the mechanical connection. On my previous small-scale prototype, where tail control was purely mechanical and based on a UK patent, I have run into issues that the mechanical connection between the hull and the sailwing caused the hull to turn into the wind, because the wind force is also acting on the tail. Another similar idea was patented by a US company, but they have abandoned it. These ideas fail when the wind is too strong.

Therefore, I think it's best to avoid any mechanical connection between the hull and the wingsail.

A good CAD software is expensive. I use Inventor.

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[andy]

Therefore, I think it's best to avoid any mechanical connection between the hull and the wingsail. - here I mean any other connection than the rotary connection.

[Ryan McKay]

Andy,

I've been pondering your question independently for some time now and have designed a relatively simple mechanism to actuate the wingsail 'tail' from inside the hull. I've attached a screenshot of a concept I built in Solidworks. It is based around using two concentric shafts; one for the wing (green) and one for the tail (red). The shafts are fixed relative to each other through the gear train (green shaft -> large green gear -> brown double ended gear -> purple gear -> blue double ended gear -> large red gear -> red shaft. The wing and tail are free to spin as a unit relative to the hull, (minus any seal friction), so the 'turning effect' you mention should be minimized. The purple gear is fixed to the hull, but free to rotate. Similarly, the shaft of the brown gear is also fixed to the hull, and is also free to rotate around that shaft.

The tail is actuated by moving the blue gear relative to the brown gear. In my model, this is accomplished by a linear actuator (modeled as a grey rectangular link). 

A video of the mechanism swinging freely relative to the "hull" (aka grey square) is shown here: https://drive.google.com/file/d/1Xcljj1ju6lnUNSSJkwZQEz8e0lUEH2je/view?usp=sharing

This model is entirely conceptual and not optimized at all. The ratios of the gear teeth will determine how much travel you can get out of a system like this. I'd be more than willing to help flesh out this design, if desired. I also have a home machine shop, if you want help with fabrication...?

Ryan

[Dicks GMail]

Here’s a scruffy hand drawing of how my suggestion could be implemented. 

In addition to the basic idea I also tried to illustrate how a watertight barrier could be achieved between the hull and the mast by using a diaphragm. I might have over complicated the drawing with the orange bits in the process. 

It assumes that the base of the mast could be raised enough to provide access by a pushrod linked to the servo or actuator. May be the base of the mast could be raised on a small platform.

As this idea only involves a single push rod positioned at the masts axis and the connection between the fixed part and the rotating part being via a a single point at the top and bottom of the small ball in line with the central axis I don’t think it could induce any turning motion. The guide sleeve would need to be a little longer than I drew it to ensure the push rod only moves in line with the axis.

In principle it’s pretty much the same as the control rod connection you find in any model RC plane except for a gap in the rod bridged by a small ball held between two small shallow cups, and the addition if a return spring to keep the gap closed.

Cheers, Dick.

Sent from my iPhone

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[Anna Friebe]

Hi,

Yes, this is an interesting question. 

We went with a mechanical solution. An actuator is mounted below the wingsail. The vertical movement of the actuator is translated mechanically via an inner mast part and ball bearings to a vertical movement on the outside of the main wing. This vertical movement is then translated to angular control of the servo wing through a connecting rod.

However I am not convinced that this is an ideal solution for the worst Atlantic storms.

/Anna

[andy]

I have read all the valuable comments and comparing it with my third solution (separate power source), I realized that all the other ideas involve increased mechanical complexity. Without a thorough testing, mechanical design skills and a good choice of materials, I think there is an increased risk in ocean conditions. The solution with a separate power source and solar panels involve only electrical complexity which I am more confident with, i.e. less moving parts is always preferable. The beauty of it is that I don't need to waterproof the mast - the mast can be just inserted in aluminum tube through the hull. Waterproofing the actuator is another story, but it's easier to waterproof a smaller moving part that actually moves only once per hour.

I think that 3W+3W solar panels on both sides of the wingsail should be more than enough. I can design the electronics with a power consumption up to 6.5 mA (that's 38 times less than the peak output of a single panel) and the wireless communication can be robust enough if I use a simple RF receiver without a fancy protocol.

[Dicks GMail]

(Resent as first time only CC group and so it’s not included on forum.)

A fourth option would be to mount the actuator  in the hull and link it to the control tab on the sail mechanically.  In a similar way that helicopters transfer control to the rotor blades via a swashplate. This could be installed at the base of the mast and transfer the actuator movement by push rod or Bowden cable to the control tab. I imagine the force required to operate the control tab are relatively small so it could be a single rod push action with a spring return. Or a double cable push pull as you did for you rudder last time I believe.

So it has some similarity to a slip ring, ie sliding surfaces or a simple thrust bearing, eg two disc with a captive marble between them, but your just transferring a low pressure push not establishing an electrical connection.  However as it would not involve any electrical connection more robust materials could be used.

This provides the benefit of all the electronics being within the hull and no complication of separate batteries, induction charging, electrical cables, etc., crossing the rotating ‘threshold’.

BTW what CAD system have you found useful for creating your drawing, is there a good cheap one around.

Cheers, Dick.

Sent from my iPhone

On 23 Jan 2018, at 09:20, andy <andrej...@gmail.com> wrote:

[Dicks GMail]

(Resent as first time only CC group and so it’s not included on forum.)

Here’s a scruffy hand drawing of how my suggestion could be implemented. 

In addition to the basic idea I also tried to illustrate how a watertight barrier could be achieved between the hull and the mast by using a diaphragm. I might have over complicated the drawing with the orange bits in the process. 

It assumes that the base of the mast could be raised enough to provide access by a pushrod linked to the servo or actuator. May be the base of the mast could be raised on a small platform.

As this idea only involves a single push rod positioned at the masts axis and the connection between the fixed part and the rotating part being via a a single point at the top and bottom of the small ball in line with the central axis I don’t think it could induce any turning motion. The guide sleeve would need to be a little longer than I drew it to ensure the push rod only moves in line with the axis.

In principle it’s pretty much the same as the control rod connection you find in any model RC plane except for a gap in the rod bridged by a small ball held between two small shallow cups, and the addition if a return spring to keep the gap closed.

Cheers, Dick.

Sent from my iPhone

On 23 Jan 2018, at 11:53, andy <andrej...@gmail.com> wrote:

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[philip...@gmail.com]

I think that your approach of putting everything in the sail makes the sealing easier, and sealing would be the most likely failure over a long time in ocean conditions. Any complexity in the radio communications can be debugged in the warm of you house, which is much preferable!

I tried a wingsail instead of a proper sail, with very disappointing results. Basically, it was much worse: the boat barely moved, it was much heaver (not least because you need to counter balance everything so it doesn't drop down to the downwind side of the boat as it heels), and more likely to be damaged by the sea. I used a mechanical cam between the steering foil and the hull, so that when the boat was on the port tack the sail was angled to propel the boat forwards, then as the boat swung past the wind (in a tack for example), the sail moved to the opposite offset, which is what you need to move forwards again. Mechanically this looked OK, in that the small foil changed angle as the sail rotated, in the correct way: and going straight into the wind, or downwind the main foil was straight into the wind. It also removed the need for anything electrical on the sail, or a link from the hull, or the boat controller knowing where the wind is.

However, the resulting propulsion force (the lift component) was very poor. I think the main reason for this is the difficulty in keeping the mainsail (foil) at the correct angle relative to the wind. I was aiming for about 8degrees angle of attack, as it is between zero (no lift) and a stalled wing (not much force, and lots of drag). I'm not sure why it was so bad, but possibly because the wind is turbulent right down at sea level, or because the main wing causes turbulence which then affects the steering foil. You may need dual steering foils to keep them out of the wake of the main foil (But even this didn't help me.) I gave up, and now have several aerofoils lying round the garage waiting for another project. Real fabric sails were much, much better and seem to cope with real wind conditions more successfully.

I suggest looking up the Ivor Bittle website. (https://www.ivorbittle.com/) who has tried out wings on model boats. He had more success than me, and has useful links to additional information.

Phil

On Wednesday, 24 January 2018 08:21:47 UTC, andy wrote:

[Robin Lovelock]

I've enjoyed reading these posts. I recommend playing the last of the videos from my "Snoopy" page on the right: the early "experimental" years from 2008 to 2011. In my humble opinion, any significant design development takes a LOT of time doing testing, rather than coming up with design solutions, or even building prototypes. We did not start discovering important things until we started 24/7 tests on a lake.  Play the video on the right :-)

Robin

www.gpss.co.uk

from "Snoopy" on www.gpss.co.uk/autop.htm .....

Snoopy on BBCTV in 2012... the full story... 2014 & Snoopy boat history... 2015 Atlantic Attempt - Why Brighton ? ... Early experimental "work" :-) 

[Anna Friebe]

Hi all,

This is also a nice mechanical solution (although patented).

http://www.sailwings.net/tl2.html

Cheers,

Anna

[philip...@gmail.com]

I did discover this (but had forgotten where I'd seen it) after I'd worked out how to do my design (because up until I worked out how to do it I didn't know what to search for!). It is pretty similar to my concept. I think the part that is patented is the option to change the angle of attack of the sail by moving the cam, to change its eccentricity. Its a nice idea, but the boat isn't exactly racing around the lake. The main difference between this and mine is that the sailwings uses a round cam, which doesn't give a constant angle of attack at different sailing directions. I used a non-round shape that gives a more constant angle of attack over a reasonable range of sailing direction. Since the sail wings is assuming an operator, they can adjust the angle of attack as the boat changes direction. I wanted mine to be autonomous and not need any intelligent control.

It is also interesting to see that on the latest Americas Cup boats, the mainsail is hinged in the middle (more or less) so that a non-symmetrical aerofoil can be generated. The sail direction is then set by one of the crew to get the correct angle of attack. Although it seems to take a lot of power to get the boat to work.

So aerofoil sailing boats can be made to work, perhaps its just me that can't! But then again, look at the ratio of sail sailing boats, to aerofoil ones, and I'm not alone.

[Robin Lovelock]

I just LOVE Phil's radical suggestion that old fashioned sails might still be popular for good reason - I certainly agree :-)

I've just added this picture to Snoopy's "Design" page. After checking that earlier old video on youtube, I was taken to one of the Austria meet in 2008, and I got a glance of my wife and I in the crowd, with me wearing a cowboy hat. Maybe I can find the old VHS tape of video shot there, including the stay in Vienna and our visit to the "Singing Toilets" at Opera Tube Station :-)

Robin

www.gpss.co.uk

from "Design" page on www.gpss.co.uk/rbdesign.htm >>>>>

Summary of design used in Snoopy's 2012, 2013, 2014, 2015, 2016, 2017 and 2018 boats ...

Experimental prototypes first sailed, on Bray Lake, in 2008, but it was not until 2012, that we had settled on the current design, used in all our Atlantic attempts so far:

• Small 4 ft / 1.2m long fibreglass marblehead hull, filled with foam: small enough to fit in back of an estate car: permits frequent tests, then a shore-to-shore Atlantic attempt.
• 3 ft / 1m high sails - strengthened standard International One Metre (IOM) #3 storm sails: small enough to function in winds of 35mph+ and survive much stronger gales.
• no sail winch servo: sails are set for sailing close to wind, with booms typically 30 degrees from centre line: less things to fail; less risk of wind damage.
• four independent electronic sub-systems, for autopilot, SPOT tracking, GPS-logging, and navigation light.
  • Autopilot based on BR-355 GPS, Picaxe 8M2 computer, rudder AS-17 servo, powered by duplicated NiMHd batteries & 130x130mm solar panels.
  • SPOT tracker was based on modified SPOT Messenger 1, with Picaxe based timer, batteries, and 130x130mm solar panel. Now SPOT Trace.
  • GPS logger (Needed to comply with Microtransat rules) based on GT-20 I-GotU logger, powered by small 100x50mm solar panel.
  • Navigation lamp (now optional) based on solar powered garden light.
• All electronics, in own waterproof containers, within the "lunchbox" at rear, above the deck.
• Rudder shaft comes up into the "lunchbox", to be driven by the rudder servo, controlled by the autopilot.

When testing on Bray Lake, additional equipment is added "just for test". e.g. the Text-To-Speech (TTS) module, which speaks text sent it by the Picaxe based autopilot, the FM transmitter, with it's microphone, that relays the speech to a transister radio on the shore; the Mobius video camera, that records the sound, together with video from the deck, showing behaviour of the boat, including steering and wind in it's sails. This extra equipment is removed for 24/7 testing, and the eventual Atlantic attempt(s).

All products used within a boat will have undergone months, sometimes years, of experimental test, before weeks or months of 24/7 test, before an Atlantic attempt. Please do not confuse what we are doing experimentally, for possible use in future boats, with our "current design" above. e.g. experiments with boat 6 to test things like compass-based steering, use of wind direction sensors, etc.

Remember that the biggest challenge to a robot boat crossing the Atlantic is reliability: maybe the most useful thing to remember is "KISS" - Keep it Simple, Stupid :-)

On Tuesday, 23 January 2018 09:20:11 UTC, andy wrote:

[Peter van den Brand]

I have also built a similar boat with a wingsail. My experience is
similar to Philip's: my boat wouldn't really sail well. And the moments
that it did sail reasonably were just by chance probably, when the wind
would briefly hit the wing at the correct angle and it would then just
drift for a little while until it stopped again.

I actually put two wings on a single boat. They can rotate completely
freely, and I had installed 360 degree rotation sensors on both. Data
logging from those sensors showed that the difference in angles between
the main wings would range from -20 to +20 degrees. The histogram of
this difference looked a bit bell shaped. That difference should have
been as close to zero as possible whenever the wind is blowing. So I
concluded that the tail wings were unable to keep the main wings at a
nice 8 degree angle to the wind.

Before I built the actual wing, I made a prototype. I put the base on
the ground and held the top part in my hand. I could really feel the
wing generating a lot of lift. However, that prototype was a lot lighter
than the eventual wing. It was just foam and some pieces of wood to keep
the tail and main wing together. No fiberglass, no parts to control the
angle, no counter weight, etc. I 3-D printed a lot of parts, and it
turned out they added a lot of weight. Two wings are heavier than one
wing with twice the surface area. And, I tried to make the counter
weight as light as possible by mounting it far in front of the wing.
That turned out to be a mistake. It's better to have a bigger weight
closer to the mast, because that will reduce *inertia*. The goal is not
the smallest weight, but the smallest rotational inertia.

Because my wings had too much inertia, they needed to much wind to
actually align themselves properly. I estimated that they need wind
force 5-6 to start working, but that hardly happens where I live so I
have not really seen them working well.

My mechanism to control the angle between the tail and main wing was
quite a simple mechanical system. There's a rod attached to the tail
wing, sticking out towards the mast. If you move this rod towards or
away from the mast, then the tail wing rotates left or right (relative
of the main wing). This rod is can slide over a ring that is placed on
the deck around the mast. That ring is not perfectly round, but as the
whole wing moves freely around the mast, it pushes that rod further or
closer to the mast, depending on the position of the wing. At a given
apparent wind angle, the angle between the tail and main wing would
always be the same, so there is no control possible (nor needed). I
figured that if I want to reduce power, I could simply steer more into
the wind.

I still think a wing sail is a very elegant solution. It's just that my
execution was lacking. And I never found the time to try to build
another wing.

Regards,
Peter

[andy]

I have tested the concept with this model boat and it worked surprisingly well:

https://www.youtube.com/watch?v=raJ1yxpB4lI

[andy]

This is the UK patent I was referring to a few posts back. This idea fails in a strong wind, because the hull has a tendency to move upwind as the wind acts on the tail and the force transfers through the mechanism. After a lot of testing, I have abandoned it and now I am going to use an actuator mounted directly on the sailwing.

[andy]

This is my explanation that I have also sent to the patent owner:

"Unfortunately, I have to abandon this system in favor of an actuator. I am going to explain the issue here. I made a video where the boat is sailing very well in a wind of 4-7 knots. But if the wind is strong enough (> 12 knots), the boat has a strong tendency to stay upwind and it's nearly impossible to turn it with just a rudder. The boat can stay in such a position for hours regardless of what I do with the rudder. I have been doing a lot of experiments until I figured out the reason. It seems this is a fundamental property of the automatic control system. I will try to explain it shortly: when the boat is heading upwind, the tail and the wing are coplanar (at the relative angle of 0 degrees). When you turn the boat a little to the left or right, the angle between the tail and wing increases from zero to, let's say, 5 degrees. However, the wind acting on the wing and tail wants to decrease this angle back to 0 degrees. This action transfers to the control mechanism which includes the eccentric disc. Because the eccentric disc is firmly attached to the hull, the hull wants to turn back until it's pointing against the wind. In physical terms, the potential energy is the lowest when the boat is heading against the wind. To turn the boat, you must act against the wind forces. Specifically, the eccentric disc is acting against the sliding surface. And why this issue doesn't happen with an actuator - because unlike the eccentric disc, the actuator is not firmly attached to the hull, but it's attached to the wing."

By the way, I have also tried it with a different shape that gives a constant angle of attack (generated in Python).

Actuator is the way to go.

[Anna Friebe]

Thanks Andy, sorry I didn't see that! Very interesting to hear of your experience!

/Anna

[philip...@gmail.com]

Although your boat suffered from this effect (heading up into wind) I don't think this is a necessary result of a mechanism to keep the main foil angled to the wind. If the main foil is pivoted on its centre of pressure, there shouldn't be any (significant) force required to get it to point at any angle relative to the wind. Therefore any force on the cam (and therefore torque on the hull) should be insignificant. You may also need the steering (elevator) foil to be pivoted on its centre of pressure, but the small force on the steering foil shouldn't be enough to turn the boat anyway. I think it is just as likely that the sail is mounted too far back on the hull and causing the boat to weather-vane into wind. I unfortunately achieved this effect by adding a second mast at the rear of my boat to try and steer automatically close-hauled, but instead it just went up into wind until it reached the edge of the pond. Just as you had, I didn't have any steering ability. My rigid aerofoil design didn't suffer from the heading up into wind effect, even in a reasonable wind (Force 4), it just didn't really go anywhere at all. 

I'm not saying that your approach of putting the actuator in the sail is wrong, and I agree that if you have an actuator to control the steering foil angle, it is probably easier if it is on the main foil. I just don't think that your boat heading into wind is a fundamental problem of the mechanical steering system.

As an aside, I'm a bit surprised at the heel angle of the boat in the video referenced above. It looks as if there is a lot of drag from the foil and looking at the speed of the boat, not a huge amount of lift. This implies that the foil is not really at the correct angle, and has probably stalled. I think this is the main problem of a symmetrical aerofoil: it only makes an efficient wing over a small range of angle of attack, so either you don' get any lift (thrust), or you get lots of drag (heeling force). I'm not sure why, but a sail seemed to do a better job in my experience.

In case it is any help, this page has a graph of lift and drag verses angle of attack for a symmetrical aerofoil It shows that stall is at about 16 degrees, which is why I aimed for an angle fo 8degrees. After 16degrees, the foils isn't really better than a flat plate. I haven't found any corresponding graphs for a sail though. http://www.aerospaceweb.org/question/airfoils/q0150b.shtml

Phil

[andy]

I believe the "small/insignificant force" you are referring to is actually large enough to turn the hull. When the boat is barely moving and the wind is strong (this combination may happen when tacking against the wind), the force needed to turn the boat is small as well. When the ocean wind is very strong, even the force needed to turn the tail becomes large (although much smaller than the force that would be needed to turn the wingsail without a tail).

The heeling angle you have seen in my video increases when the wind is blowing close to the bow or stern, because the lifting force that the wingsail produces is large. In this case, the lift (not drag) of the wingsail causes the boat to heel. If the wind is blowing to the port or starboard, there's barely any heel.

It looks like our confidence in the wingsail depends on our own experience which is different in some aspects. Based on my experiments with the prototype, I am confident in my current design and hopefully, it will be finished this summer.

[Dan Gurau]

Hi Andy

I just dismantled an old IP camera (it's a PTZ, it can rotate on 2 axis).

I noticed it has a bunch of wires for power & data going to the upper part.

However, you can rotate the upper part forever, there's no "wire" going up.

It seems to me this is what you need.

See attached.

Regards,

Dan

[andy]

I think it's this option from my first post:

2) Use a slip ring

Pros: It solves the above problem with the flexible cable.

Cons: The slip ring must be IP68 waterproof and very reliable at the same time, which looks like a point of failure. The rotary seal would also add resistance (the wingsail is free-rotating and it must always turn in wind direction). It's likely that the rotary seal will fail after billions of small oscillations.

I have just designed a wireless actuator controller and it works like a charm! I am going to use a separate power source inside the sailwing.