A Panemone (Drag-Type Windmill)
This project has been through 4 revisions so far, with 3 actual constructions
completed. Each of the three has been blown apart by the wind, but the
latest one has been standing (and turning) for more than 12 months.
A "PANEMONE" is defined as a device which derives its energy from the wind
in such a way that the wind-catching vanes move IN THE SAME DIRECTION as the
thrusting force of the wind (this is called "DRAG"). This is in contrast to the motion of
a propellor, whose blades move AT 90 DEGREES to the thrust of the wind
(this is called "LIFT").
The only problem is that most panemones, when they are turning, have some component of
DRAG, as well as some component of LIFT. So, a rather better definition of a Panemone
is: The axis of rotation is at 90 degrees to the direction of the wind. (The rotating
shaft lies ACROSS the wind, whereas with a propellor, for instance, the shaft points
directly INTO the wind.)
You can see from the diagram above, that the wind will push against the
panels when they present themselves across the wind, and the panemone will
rotate in the direction shown. When a panel reaches the furthest downwind
point, it will "jibe" like the sail of a boat when it turns across the
wind. Then, on the "upwind" beat, the panel will remain feathered into the
wind, until it reaches the most upwind position again. Then the panel stops
feathering, because it reaches the stop peg which forces it to present
itself across the wind again for the next "downwind" beat.... (and so on).
My panemone has FOUR arms, and looks like a cross between a rotary
clothes-line and a
square-rigged sailing boat. My daughter Jean has painted the panels
in wonderful psychedelic blue, purple, red and yellow swirling patterns,
(blue/purple on one side, red/yellow on the other) - and they make a
striking display when the wind blows them round and round....
I had thought that this design was unique, until one day I was browsing
in the Massey Uni library, and found that the Chinese have been building
panemones very like my one since about 800 AD.... (for pumping water).
Oh, well - I guess a Good Idea is one which gets re-discovered many times!
One of my favourite pastimes is to sit on a deckchair by the windmill
with a cold glass of homebrew in my hand, in a stiff breeze....
The entire structure is supported by a central steel pole (3.5m tall)
eight guy-wires staked firmly into the ground. The pole rests on the top
of a fence-post driven all the way into the ground.
The top of the pole is capped with a steel washer, which has a 16mm steel
rod through it. This supports a conical thrust bearing (from a motor
car hub), which in turn supports the entire rotating structure.
Most of the central support structure is made of 100 x 50 framing timber,
and each pair of arms is made from four lengths of the same timber, 6m long.
(Two lengths to support the top and two lengths to support the bottom of
each panel.) Everything is nailed together as shown in the diagram.
Each of the four panels is made of 75 x 25 timber for the frame, and a sheet
of 3-ply (which has been painted wonderfully as you can see from the
photos.) Each panel is 1.2m high by 2.4 m long.
The panels are fixed to the arms by a steel rod and bearings as shown, and
they swing freely until they stop against the flexible plastic stop pegs.
The stop pegs hold the panel into the wind in a moderate to strong wind, but
allow the panel to "break away" when the wind is too severe. The panel then
feathers, to prevent damage to the structure. (Neat, hey?)
I haven't connected the windmill to any power generating sytem yet,
but I've got a couple of ideas about how to do this.
I have a permanent magnet washing machine motor (just like the one I used
for my pelton wheel - see that project), which works as a generator nicely.
The generator needs to spin at around 400 revs per minute, and since the
windmill goes round at a stately 4 revs per minute, I need a pully and belt
system which steps up the rotational speed by 100 times!
I hope to do this with two steps of 10:1 each (which makes 100:1). But
I'll write more about this here, when I've done it.
After my panemone had been working for a year or so, we had a VERY strong wind (which
blew down lots of old trees in the district and did a lot of damage to buildings and
powerlines), and my poor panemone couldn't cope. The panels all feathered, just like
they were supposed to do, but then they began to oscillate madly from side to side,
the whole structure weaving crazily as if it had a life of its own! Then a guy-wire
snapped, and it was all over...
A couple of homebrews later, a new idea and a new panemone rose from the ashes
This one is a HORIZONTAL AXIS Panemone. It looks like a ferris wheel, or perhaps an
upside down paddle-steamer :)
The idea is to place a wind-shield around the base of the structure, so that the wind
only blows on the TOP HALF of the machine, and blows the paddles round. Our wind almost
always comes from the North-East, so the panemone faces that way.
I've built the paddles from blue tarpaulins which will tear off in a very strong wind.
This hasn't happened yet!
I'll put more pictures up here when I've built the wind-shield....
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