Torque Sensing Variable Pitch Hub Designs

[clintonbriley]

Lately I've developed an interest in (passive) variable pitch hub governors. 
Most of these are actuated via centrifugal force as a result of change in
rpm and I like those designs for their specific merits, but I am
primarily interested in a design that can regulate torque without regard
to rpm.  From what I gather this type of governor would not be of
much value for an axial flux wind turbine, but it could be very useful
for a "constant speed" (asynchronous generator) wind turbine with an oversized
rotor for a given generator size.  The only torque based design I've been able
to find which might perform this task (on an up-wind rotor) was patented in 1925 in an
effort to regulate voltage......  http://www.freepatentsonline.com/1533467.pdf
Are any of you aware of any other passive vari-pitch designs which are torque
sensing/regulating?
Thanks,
Clint

[Harold in CR]

 The unit I first built, in the '70's, had that Centrifugal Governor system. I had several failures of the joining coupler, from the Gearbox to the Alternator. I had a total of 15' blade span, and, when the coupling broke down, the prop would run at a pretty much steady speed, judging by the whooshing sound. I guessed, and used Field Tiller Springs, one on each blade. I cut off about4 coils and bent the last coil to form the right angle needed to connect to the hub ring or Eyebolt.

  I watched the output of the machine, once I get the coupler thing engineered correctly, and would climb the tower, pull the machine out of the wind, and tie a blade to the tower. Then I would adjust the tension on the springs counting the turns, until I finally had the machine actually stall at 127 volts AC, maximum RPM's.

  This one I am building is smaller, and the springs will be lighter tension.

  Guess this long writeup is saying, I believe if you get the nearly correct tension springs, and fine tune the governor, you will have that steady Torque, at whatever the STEADY wind speed might be. That wind speed is where you might have the most trouble. It is always varying.

  Hope this might give you an idea of what I found.

[clintonbriley]

Thanks for the input Harold, but the hub governor I have in mind would regulate torque at a fixed rpm.  So there would
be almost zero variance in centrifugal force.
Clint

[clintonbriley]

Here is a basic sketch of a torque governing hub idea that I think might work. 


So do you think it could work?
Clint

[Harold in CR]

 I could be wrong, but, the way you drew that, one blade would twist one way, the other blade the opposite way

 The original Jacobs Flyball Governor had one weight and 1 set of gears for each of 3 blades.

 Might be redundant, but, what about a Hydraulic pump hooked to the blade. Hydraulic speed control governor to a motor that drives the generator ??  That would give you absolute control, above a minimal wind speed ?? Just rig up a small reservoir and put it in the tower, out of the way ??  I always wanted to try that kind of set up.

 Just make the blade bigger, to allow for the Hydraulic bits ??

  I could never understand when most people are splitting hairs on refining a system. If it takes a tad more to accomplish something, Build the Blade a tad larger to compensate   Maybe it's just me ??

 I'm tired from sawing logs all day, so, I will have to go back and read your original post, to see what you are trying to do.

[clintonbriley]

Hey Harold, the gears mesh exactly the same way as the jacobs flyball governor, although they are set up differently to create a
var-pitch hub controlled by torque rather than rpm.  On the jacobs fly-ball hub, the job of the center gear is to allow the
moving weights (fly-balls) to pitch the blades and keep them synchronized.  On my proposed hub, the center gear actually drives
the main shaft as well as pitching the blades and keeping them in sync.  On a grid connected turbine with an asynchronous generator,
the generator will regulate the speed as long as the input torque is kept within a given range.  The large commercial turbines mostly
rely on active pitch control which is computer controlled, and the smaller commercial turbines typically use a blade which is designed
to limit torque with passive stall design.  The passive stall blades are a great solution because they require no extra moving parts, but
the blade needs to be perfectly matched to the generator and as I understand it can be very difficult to design with lots of trial
and error involved in perfecting a blade for a specific generator/drivetrain combo.   To make a turbine more feasible for a low wind
area, it would be desirable to put a much larger than normal blade set for a given generator.  The problem is that it becomes more
difficult to shape the blade so as not to overpower the comparatively small generator when winds are good.   If this hub were
to perform as hoped, it would make it easier to use a larger set of blades while making the turbine more efficient in lower
speed winds.  One side benefit of this hub design is that when the brake is engaged, the rotor blades would immediately pitch to
feather (until coming to a stop) reducing the load on the brake when winds are high.  I must confess that one design that I've
had in mind for this hub design is the breezy 5.5 and since I don't live in a great wind area, if I were to build one, I'd
like to use a much larger rotor than would be considered standard.

Clint

[Ungrounded Lightning Rod]

With a constant mag field from permanent magnets, a torque-regulating hub would regulate output current, not voltage.

(This is probably just what you want in either a battery-charging or direct grid-feeding mill.  It amounts to furling - ideally just below long-term current limit.  Voltage is regulated by the grid or the batteries.)

[Perry1]

I have worked out a similar method to pitch the blades for a constant torque input that is very simple. As with all these 'variable pitch' threads, I worked it out but never built it, HA! It was more of a thought experiment I guess.
For me the kicker was that it eliminated the key function of overspeed protection. Perhaps you are thinking of torque limiting and a furling setup.
If I can ask, what is the functionality you are looking for and how much more efficient are you expecting the turbine to be in order to make up for all the added complexity? I don't really see the need for a variable pitch system on turbines of less than 100 kW. For our 'micro' sized turbines all the supposed perf gains can be had by adding half a foot to the blade length.

They are fun to think up though

Perry

[clintonbriley]

 Hey Perry, I'd love to see your design.  Do you have any sketches here on fieldlines?
 
I've played with some hub concepts which would combine torque governing with runaway
protection, but simple torque governing is all that is needed to solve the problems listed
previously.  I think it is quite likely that I am covering ground that has already been well
covered by others in the recent and/or distant past, but aside from the patent I listed in the
beginning of this thread, I have found no information of others as yet.
How much more efficient do I expect a turbine to be with this hub installed?  Well if it works
as desired, that would depend.  For starters it would depend on the wind speed in a
particular area and the design of the particular turbine.  It would depend on how much
you could increase the size of the rotor on a particular turbine.  No doubt there are situations
where this modification would not pay at all and there are others that it may increase
production by many fold.   
So Perry, lets see your version of the torque governing hub!
Clint

[Perry1]

Hey Clint,
there is a thread on here somewhere but no sketches or anything. I have it in CAD at home on my computer but nothing really special. It's pretty easy to describe. Imagine two discs one connected to the gen the other connected to a ring gear. The blade shafts have ponions on them that engage the ring turning the rotor disc moves the ring relative to the gen mounted plate. The two plates are connected with a torsion spring. Like a clock spring. As the gen loads up the blades move from bite to feather position.
I know, that's probably a terrible description. Once again, I couldn't make a case to take this any further. You suggested it could increase perf many fold. How so?

Perry

[clintonbriley]

Hey Perry, your description sounds a lot like the concept I sketched here.  You asked how performance might be increased
many fold.  For starters, if you can increase your swept area by a factor of 2 or 3 that would increase your potential power
from the wind by at least 2 or 3.  The example I was primarily thinking of is once again the prairie wind turbine (breezy 5.5).
One of the guys who is a member here has posted his experience with his breezy and with his being in a marginal wind
zone and the breezy really only working well in a med-high to a high wind zone, the winds were just shy of allowing his
turbine to kick in much of the time.  If a larger rotor allowed just a bit more power to be extracted from the wind, his
production would likely have gone up a lot since the average hours of producing electricity probably would have increased
significantly.  A good hub governor would also allow much more efficient blade profiles to be used than they currently use.
Tom made some really nice blades and they did improve the performance in lower winds, but they overpowered the
generator in just moderate winds requiring it to shut down.  So like I said, it depends.  Some turbine designs could
benefit greatly from a good hub of the sort we've been discussing.  The breezy design is great for high wind areas
and it can be built on a fairly modest budget.  If a much larger set of blades could be governed by the type of hub
we've been discussing, I think it could be a good low wind machine as well. 
So Perry, can you post a sketch of your hub so we can all see a little better how it works?
I'd also be interested in seeing how you also designed it to govern over speeding while unloaded as well.
Clint

[Perry1]

Hi Clint,
My idea was very much like your drawing. I would almost say exactly like your drawing. Problem is that this style of moderation does NOT address overspeed control. I guess it may in the form of if your generator is applying too much torque to the rotor the blades will feather but an induction machine like the Breezy wants a constant speed much more than constant torque applied to it.
The Breezy's blades are inefficient because they are designed to be. Aero braking is their main means of overspeed control. This takes the turbine into a higher wind regime but that's the tradeoffs of turbine design.

Perry

[tecker]

 I have a  washing machine clutch on the bench .It's centrifugal but I think it might make a good interface to a blade hub .I had it in mind for a steel core  a clutch is not much of a factor with a air core   

[clintonbriley]

For me the kicker was that it eliminated the key function of overspeed protection.

Hey Perry, I thought from your previous post that your design also employed overspeed protection.
So it's also just a torque governing hub like my sketch then?

I guess it may in the form of if your generator is applying too much torque to the rotor the blades will feather but an induction machine like the Breezy wants a constant speed much more than constant torque applied to it.

The asynchronous motor/generator is commonly refferred to as a constant speed generator.  In actuality
it's a constant "range of speed" generator.  Rotor slip is what allows an induction motor to function as a generator
and the rpm of the motor/generator will vary by a few percent of its rated speed between its minimum and
maximum generating capacity.  So the rpm is determined by the amount of torque driving the generator.
If the torque is too high, the rpm will be higher than the maximum allowed rpm limit for the
generator to make grid quality power and it will send lots of destructive harmonics to the grid.
I understand the power company doesn't like it very much when this happens :-).

The Breezy's blades are inefficient because they are designed to be.

Yup, and that's the price you pay for passive stall (or perhaps a less than optimally
efficient passive stall blade design...I don't pretend to know much about designing a
set of passive stall blades),  Which is why a torque governing hub (still making the
asumption it would work of course), would allow the use of more efficient blades with
a larger swept area. The blade diameter could be made quite a bit larger while still using
the same built-in gear ratio (14.55 to 1) by switching to a 3 blade or larger still by switching
to a 2 blade rotor.
Clint

[clintonbriley]

I have a  washing machine clutch on the bench .It's centrifugal but I think it might make a good interface to a blade hub .I had it in mind for a steel core  a clutch is not much of a factor with a air core

Hey Tecker, I'd like to see a picture or sketch of the part you are talking about.  Is that doable?
Or maybe you could describe it?
Clint

[clintonbriley]

With a constant mag field from permanent magnets, a torque-regulating hub would regulate output current, not voltage.

(This is probably just what you want in either a battery-charging or direct grid-feeding mill.  It amounts to furling - ideally just below long-term current limit.  Voltage is regulated by the grid or the batteries.)

Hey Ungrounded Lightning Rod ,
So I guess this hub would be universal then.  At least it could be if overspeed protection was also built into it. 
It could eliminate the need for a furling tail and allow the turbine to keep running in higher winds while protecting
itself from flying apart when spinning with no load. 
Realisticly though, for a conventional axial flux design, ***IF*** one were to employ a hub governor, is there any
advantage to a torque sensing/torque governing hub?  Or would a centrifugal type rpm limiting hub (like a jacobs
flyball hub) work equally as well in that situation?
Clint

[clintonbriley]

It just dawned on me that the basic sketch I posted earlier which illustrates a two blade
hub almost identical in fuction to one variation of a standard right angle gearbox.
So with just a little modification this could be used as the hub discussed in this thread.
At least it could be used to determine if the concept is viable or not.




Clint

[clintonbriley]

On my proposed hub, the center gear actually drives
the main shaft as well as pitching the blades and keeping them in sync.

My mistake, the spring is what drives the main shaft, at least until the upper
stop limit is reached, then it would be the hub that drives the shaft.

Rotor slip is what allows an induction motor to function as a generator
and the rpm of the motor/generator will vary by a few percent of its rated speed between its minimum and
maximum generating capacity.

The rotor slip is apparently closer to 1 percent than 3 percent of its rated speed, between min and max output.

[Ungrounded Lightning Rod]

I have a  washing machine clutch on the bench .It's centrifugal but I think it might make a good interface to a blade hub .I had it in mind for a steel core  a clutch is not much of a factor with a air core   

I'd expect it to have two issues:

 1) It's designed for a higher speed.  You'd have to replace the springs with something much lighter.

 2) It's designed for something that runs at essentially a constant speed, significantly above the clutch cut-in.  You'd have to check that the shoes are set up so the clutch "locks up" - the forces from friction as it engages causing it to tighten up, rather than slip as it engages until the speed is up further.  (I'd expect it to work that way but it's something to check.  If it doesn't it will quickly burn itself up in winds where it's JUST engaging.)

Of course the "motor" end has to be hooked to the blades, not the genny.  But you knew that.  B-)

[clintonbriley]

Some of the curtismachine gearboxes like the one in the illustration above have this gear
configuration available......


This one has four intermeshing gears.  Because there are several different optional gear
configurations and ratios for the same size case (STRAIGHT BEVEL 1:1, 1.35:1, 1.5:1),
it looks to me like it might be possible to use either the (1.35 to 1) gear sets or (1.5 to 1) gear sets
instead of the 1 to 1 ratio gears in this illustration to make a 4 blade variable pitch hub.
To do this would require some decent machining skills (and machines).  It would require
boring a hole through the case/box to install another (thru) shaft and installing bearing flanges
and another gear (for a total of 5 gears).  The larger gear would mount on the newly installed
thru shaft, and the smaller gears (4) would replace the four 1 to 1 ratio gears in the illustration.
Depending on how curtismachine builds these boxes, it may or may not be neccesary to do
additional machining to get the 4 gears (no longer intermeshing with one another) to mesh with
the newly installed larger gear. 

Ok, even I have to admit this is getting a little too complicated, but I thought the idea was
interesting enough to throw out there even if it isn't really practical.
The curtismachine site also says they can make any custom gearbox with angles other
than 90 degrees, so I'm sure they could build a more ideal 120 degree version for a 3 blade hub.
(For a slightly higher cost)..... ;-)
Clint

[Perry1]

Thus my original post.
About twice a year I get the variable pitch bug but sooner or later cooler heads prevail. Awesome on paper but never one built, at least by me and on a small scale.

Perry

[clintonbriley]

Yeah, I know what you mean Perry, I've had lots of false starts in the past too.  Mostly
because I wasn't aware that there were still more critical things of which I wasn't aware ;-)
I'm still working on some ideas though.  After looking at the possiblilty of incorporating this
design into a 2 blade teetering hub for several days, I decided that it couldn't be done.
But I was out cutting hay today and I came up with some new ideas that might just
pan out.  Hopefully I'll be posting a new design in the next couple of days.
Clint

[clintonbriley]

While looking online at some other 2 blade designs, I found the website for Wes wind turbines.  I was specifically looking
for 2 blade teeter type turbines to how they are built, but the Wes has what they refer to as a "flapping" system.
Frankly I don't quite understand the flapping concept.  It sounds like it's done partly as a fix for wind shading
at the tower, but I don't know how it would apply it at all to the vibration that teetering addresses.

The hub is a passive variable pitch design for a constant speed turbine, and it uses the same basic method of torque governing
as the hub I have been discussing here.  This further convinces me that the hub design I propose will work.

The website is here... http://wes18.com/index/47/rotor
It has a youtube video showing the passive pitching mechanism in motion.
Does anyone care to comment on the flapping thing?
Thanks,
Clint

[clintonbriley]

Ok, it took me while to understand the flapping thing.  In theory a teetering 2 blade hub puts almost no cantilevered load on its
shaft.  In actual practice springs, shock absorbers, and rubber bumpers will deliver some of this cantilevered type of load
to the shaft, but as long as the blades don't teeter past their allowed range of motion, the applied force is kept extremely low.
   Because movement of one blade on the "flapping" blade hub causes the blade opposing it to move in the opposite direction
than a teetering hub would, I initially thought the cantilevered force delivered to the shaft would be even greater than that seen
using a fixed 2 blade hub.  I understand now that is not the case.  The force applied to the shaft by the flapping blades is
significantly greater than that of a teetering hub, but the overall levels of force are still much lower than they would be on
a fixed hub.
Clint

[clintonbriley]

Here is a revamped version of my basic hub design to integrate it into a teetering hub design.
Here's the sketch:



This uses a standard gearbox for the blade pitching.  In this version the gearbox would be
pretty small and mounted in a larger welded steel hub.
By partially decoupling the gearbox shaft from the input to the 90 degree gearbox, a fly weight
assembly, (also partially decoupled from the gearbox) can be made to add unloaded
overspeeding protection as well.  By partially decoupled I mean using plates with min/max stops
so that they will only move the pitching gearbox input shaft in one direction and another spring at
the gearbox will be responsible for returning the pitching gearbox input shaft to a normal running
pitch position.
Clint

[clintonbriley]

I don't know how I missed this posting by methanolcat made in 2007, but here is a link to that post
in which he has posted several pictures of a torque sensing pitch governing hub.
Very cool.
http://fieldlines.com/board/index.php/topic,140114.0.html

Clint

[don1]

Clinton,

  They already exist. Air craft use a variable pitch propeller.   Only they call it a constant speed prop. It is operated using the oil pressure from the engine through a governor.  It might be worth a look see to study how they work and maybe you can adapt some already made engineering to you hub.
   In as much as I am a proponent of the KISS method it is good to see others doing there best to get turbines under reliable control.
   Lord knows there are a lot of governing devices out there and most of them are high maintenance. or very expensive.
   A couple of years ago at the renewable energy fair near Amhurst WI   I saw a system where on a down wind machine they had the blades mounted on rubber bars and the theory was the rubber was strong enough to hold the blades in place until the wind velocity increased and then the blades would bend down wind. Now that is KISS if I ever saw it.   Anyone know of this machine and how it faired out?
  Best of luck and have fun playing with it.  don.

[clintonbriley]

Hey Don, I agree that keeping it as simple as possible is a good idea.  I've looked at a few
patents relating to airplane props and one or two of helicopter rotors, but the best info
I've found so far have been in the designs made specifically for wind tubines.  The only torque
governing hub I've found so far in commercial use is the WES rotor hub that I listed a link
to earlier in this thread.  It's about as simple as you can make for a flapping two blade wind
turbine.  I'm not keen on making a flapping rotor hub and while I seriously considered
making a pitch controlled two blade teetering hub, I've read too many articles that indicate
teetering blade concept can be a finicky system to design and it might take more trial and
error than it would be worth for me.  The pictures that methanolcat posted in 2007 shows
a hub that is actually quite similar in function to the WES rotor hub with the exception that
it's a fixed blade design and the blades pitch to stall instead of feather.  For the moment, a
three blade pitch to feather torque governing hub is my goal.  If I can make it work, overspeed
protection can be built in to it later.  The basic concept is simple enough, combine the
appropriate aspects of a Jacobs flyball hub with the WES rotor hub and keep it as simple and
easy to make as possible while also keeping the weight within reason.  I haven't seen the
downwind turbine with rubber mounted blades, it sounds interesting.  I'd be interested as well
to know if it worked out in the long term.  If you find out, be sure and post.
Thanks,
Clint

[don1]

Clint,

    I will be sure to post any info I may find on the rubber mounted blades.
    I don;t remember if there was also a metal hinge in that system but if not I can't see how good blade pitch would be maintained with just the rubber part.   Once again good luck with your project.   don.

[wdyasq]

I'm pretty sure the 'rubber mounted blades' on a downwind machine is a "Proven" brand machine.

I collected a few of the patents on Variable-pitch wind machines here:

http://www.anotherpower.com/gallery/Variable-Pitch

Ron