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#Post#: 110--------------------------------------------------
Re: Seagull DIY Discussion
By: ldissing Date: July 15, 2013, 1:14 pm
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Why would steel rods be a very bad choice? Too much weight?
BTW, I'm not modifying the design because I don't like to follow
directions, I "think" I'm doing it out of necessity. But, I
haven't drilled the holes in the ribs yet, so I am open to doing
it the right way. How straight do the dowels need to be? 1/8
inch out of straight is fine, or perfectly straight?
@crazyguy:
Nice looking picture there, is that balsa wood? If it isn't,
isn't that going to add a lot of extra weight?
#Post#: 112--------------------------------------------------
Re: Seagull DIY Discussion
By: ldissing Date: July 17, 2013, 12:25 pm
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I figured metal dowels might be a little heavy...I finally found
4 perfectly straight wooden dowels and two that are off a tiny
bit but not much.
I've never worked with the fiberglass resin...will try it out.
Don't have all that much to do.
I understand the mounting issue, but not the concentration of
magnetic flux on the opposing side but I'm no expert on
windmills. I've never seen it explained anywhere. Some folks
use two rotors with opposing magnet poles on the rotors which
would make for a strong magnetic flux though the coils and
possibly metal on the outside, but I am just having issues
finding out "why" on the web.
Thanks,
Leroy
#Post#: 114--------------------------------------------------
Rotor plates
By: ldissing Date: July 17, 2013, 1:42 pm
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That is the explanation I was looking for. Thanks. Not sure
I believe it 100%, but I had not seen it anywhere and I'd been
looking pretty hard for it.
Thanks again.
Leroy
#Post#: 116--------------------------------------------------
Re: Seagull DIY Discussion
By: lynx wind Date: July 17, 2013, 9:52 pm
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Very good conversation. I'll butt in just a little.
A dual magnet plate would increase voltage about 3x, but is much
more complex. What I have found with this type of VAWT is that
the turbine will spin up to provide the voltage you need. If
there is 12 watts for this size turbine in a given wind, the
turbine will run up to an rpm where it outputs as much as it
can. I find that at the lower end of the power curve this is
30-35% of the power in the wind (which is quite good).
If you go to the trouble and expense of making a dual magnet
rotor the turbine will just run slower and still output the
same.
So, for simplicity I suggest the single plate rotor. And yes
the steel backing plate concentrates the field better through
the coils.
The wood dowels? They really don't do very much. They really
just serve as hard points to handle the stress and torque at
high speeds. The dowel between the rotor and tip is just there
and does little. The major stress is taken at the
rotor/dowel/rib/skin join. Maybe a 1/4 of that stress is
carried at the blade tip/dowel/rib/skin join. The torque and
outward stress is transferred down the brace to the rotor.
The dowels also help the blades resist the yaw they can
experience at high speed, (where the upper tip starts leading
ahead of the lower tip) This can setup a nasty vibration.
So if you use steel rods, you just add weight, slowing the
responsiveness of the turbine. Don't skimp on the bracing. I
now use stainless steel straps that are 7/16" wide x 22 gauge.
I also run a stud 1.5" down the dowel and epoxy it in. Then put
a lockwasher and nut on to hold the brace.
On the production Gulls I use fiberglass rods with stainless
studs epoxied in 2".
#Post#: 117--------------------------------------------------
Re: Seagull DIY Discussion
By: ldissing Date: July 18, 2013, 6:00 am
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Believe me...you are NOT butting in.
Thank you for your insights.
Leroy
#Post#: 120--------------------------------------------------
Re: Seagull DIY Discussion
By: ldissing Date: July 20, 2013, 9:07 am
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I do believe the design allows for modification fairly easily.
I happen to have NIB that are 2.5" diameter and 1/2 inch thick.
I also have 12 NIBs that are 1/2 X 1/2 X 2. I WAS going to
use 15" round plywood and put 6 of these on the rotor (made that
for the magnets already), but have decided to do it closer to
the intended design. I have read quite a bit about 3 phase and
single phase that I decided this was too big a modification.
Even if I did do it, it may not have worked very well and I
don't want to waste those bigger magnets. Besides, if I were
going to do a 3 phase design, I'd have needed more magnets.
Most say single phase designs are not very good, and we ARE
wasting some space on the stator by not having the coils bump up
against each other, but maybe this was intended. Since it is
possible to change out the rotor and stator, I will try this at
another time.
So, I've opted for putting two of those 1/2" magnets together
and creating a 1" magnet but they are twice as thick as the
design calls for which is 1/4". I don't know if that will
cause any significant problems as long as the metal plate is
3"16" to 3/8" thick. I'd prefer not to have to go buy more
magnets, but I probably should given they are $30 on the Lynx
web site. Again...it is add a "little" more weight, but I'd
like to get something working fairly quickly.
When building the airfoils, it does not say to put the dowels
through the rib formers while gluing? I assume you would do
this, but I could be mistaken. Would like that clarification
as I am ready to form those airfoils.
@crazyguy
I don't think you needed saving as he agreed with everything you
said for the most part. Heavier rotor requires more wind,
lighter requires less.
Thanks,
Leroy
#Post#: 121--------------------------------------------------
Re: Seagull DIY Discussion
By: lynx wind Date: July 20, 2013, 12:33 pm
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Yes, it is true that 3 phase is more efficient than single phase
in generator design (especially in instances where you will use
the DC directly). But this Seagull 75 is a special case where
we intentionally want to pulse charge our battery with spikey
voltage. With three phase you need to hit a cut-in rpm and at
that point the voltage is so smooth that the turbine will stall
at that rpm until there is more wind. With single phase even
though a volt meter will read 7-8 volts you are getting 13-14
volt peaks.
With this type of VAWT it will spin up to the point where it
will match the power in the wind.
So while it is common to state that 3 phase is better, single
phase is better in this design to keep cost down, simplify, and
allow the turbine to turn through a much wider speed range.
I found it awkward to glue the rib formers in place with the
dowels in. Much better to focus on getting the airfoil rolled,
smooth and square. Use a fast set epoxy to glue the ribs on the
poster board. You can staple the TE while the epoxy sets. When
all the blades are done you can slide the dowels in.
Keep in mind that fiberglassing the blades with a fillet to the
rotor provides little strength compared to the bracing. The
fillet is more for looks and smoothness. You could actually
delete the fillet and just resin the blades separate it is so
unimportant. The braces are key to success.
#Post#: 122--------------------------------------------------
Airfoil
By: ldissing Date: July 20, 2013, 2:20 pm
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I'm surprised that you found it easier...but to each his own.
I left the dowels in and found that to be much easier for me.
I did forget the 1.5 inch stud (as you called it I believe)
which would allow for placing a bolt in the top of the airfoil
for the strap, Ill just have to put wood screws in I guess.
Only two airfoils are complete and I don't have the materiel to
do any more right now, so I guess I'll chance it with the rest.
However, I do not have the straps at this time, but I will get
some.
I'm surprised those straps don't have some weird vibration when
going around in the wind, but I will use them and see how it
goes.
Thanks,
Leroy
#Post#: 123--------------------------------------------------
Re: Seagull DIY Discussion
By: lynx wind Date: July 20, 2013, 3:38 pm
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Very little happens inside the turbine. It is quite calm. Most
of the wind is compressed around the perimeter. That's why the
straps don't bother anything inside or flutter. You will notice
this turbine is very quiet, silent.
For fun, when you get this going put some telltales inside and
on the blades. Colored ribbon or string.
The blades are always attempting to run perpendicular to the
axis, but they can't. This is the force turning the rotor. The
most force is into the wind at the windward side. Once the
turbine gets past tsr 1, the whole perimeter is powering the
rotor. You'll notice a slight shudder right at tsr 1 before the
turbine goes to higher speed. The design is such that we don't
want to start charging until we are past tsr 1. Tsr 1.5-2.25 is
the power band.
#Post#: 124--------------------------------------------------
Re: Seagull DIY Discussion
By: ldissing Date: July 20, 2013, 9:31 pm
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All airfoils finiised....just need the rotor and the
stator/coils and I'm off. Will let you know.
Finally doing something worth while, I hope.
Leroy
P.S. I was trained in "college" as an EE, but that does not
"mean" anything. I do know something about circuits and will
show you an additional circuit when I have the time that may be
useful for this application. Not needing batteries is a "big"
deal. Your circuit will work, but there maybe a simpler circuit
you can utilize for the GTI.
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