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DaveP68
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Posted: 15 June 2018 at 10:34am | IP Logged Quote DaveP68

*** ding ding *** nothing about winning here in my view. Concentrate on that outer 3rd of the blades when it comes to all of the above...

Edited by DaveP68 on 15 June 2018 at 10:36am


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Posted: 15 June 2018 at 10:49am | IP Logged Quote Warpspeed

Oh I think a successful project can be viewed as a personal win.

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Posted: 15 June 2018 at 11:07am | IP Logged Quote Madness

This Calculator from Warlock Engineering is very comprehensive and should give you correct angles and cross section.

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Posted: 15 June 2018 at 1:24pm | IP Logged Quote yahoo2

BarkyJ wrote:

@Yahoo2 do you happen to have a picture of what you did with the whipper snapper cord? Really curious to see.





no photos. Usually the line would be forward of the arrow I have marked. I would superglue it on, test it, when we were happy with the diameter of the filament and the position add a bit of filler and tape it down.

It is kind of hard to explain, you are trying to max the lift and minimize the drag, sometimes a very thin layer of turbulent air gives a lower drag number than trying to "stick" a laminar flow right to the tail. Think golf ball, car rear boot lip, vortex generators.

The shape of the leading edge dictates the % split of air going over and under the blade, plus the natural turbulence in the air the wind turbine is running in plus the load on the generator slowing the rpm, that all changes the position of the line.
I had prop tape with me most times because insect impacts would damage the edge of some blades and it was a quick fix.

I might have a photo of a really nice Chinese blade with the line molded in, it is probably archived, I am not keen to dig it out unless you really need it.


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DaveP68
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Posted: 15 June 2018 at 5:45pm | IP Logged Quote DaveP68

Can anyone shed light on blade weight to help out James?

Most of what I've posted over the last 2 days mostly reflates to this important fact.

A "personal win" for me if we want to focus on these (not my intention) is how accurate my guess of 5 kg's was for the blade weight, as it ending up being 4.5 kg's.

At a current "per blade" weight of 4.5 kg's the Centrifugal force acting on the hub will be 1887 kg's at 500 RPM. That's A LOT of force!!

If the blades go into runaway and they reach 750 RPM that force "per blade" goes up to 4250 kg's!! At 1000 RPM it climes to a whopping 7550 kg's and that's "PER BLADE"!!

Blot them down carefully, as a blade coming off has the potential to travel some distance before it comes to a sudden stop! Heaven forbid through the windscreen of unsuspecting car travelling nearby...

My intention here is not to scare James at all as I'm right behind him. Everyone to date has made equally valued contributions.

Just hoping someone out there can give some advice on this one as I could be over thinking this one and James will be fine with what he's put together so far.
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BarkyJ
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Posted: 15 June 2018 at 7:05pm | IP Logged Quote BarkyJ

Yep those are certainly scary numbers.

500RPM already scares me a bit, so I likely won't let it get even that speed, to start with at least. I will just turn it out of the wind earlier with my turret control. But yes, if that fails for whatever reason and things go pear-shaped, it's certainly something to be well aware of and figure out what to do about.

Each blade is bolted with 3 bolts in a triangle pattern, to the main steel hub, as well as having steel runners going out 400mm or so, so there are 7 bolts in total. At this stage they are 8mm, is what the plan is for.

I do need to think of a backup plan if the motor fails and what to do to get the windmill out of the wind and disabled, in case of an emergency.

The plan though is to turn it out of the wind as the speed increases, so I can then run it at say 20 degrees or 45 degrees etc to the wind, as I see fit, or 90 degrees if required. Leaving it up to the mercy of self direction by tail/wind does scare me, but at the same time relying on mechanical also is also somewhat scary. I have more thinking to do, but I am still going with a motor driven turret, and no tail.

At least so far.
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Posted: 15 June 2018 at 9:34pm | IP Logged Quote Madness

Are you calculating the centrifugal force at the tip? It will much less as you get closer to the centre.

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Posted: 15 June 2018 at 10:20pm | IP Logged Quote yahoo2

I think it is more likely to flutter and flex the blade close to the root above the clamp plates which could form a crack.

If the turbine will hold with the phases shorted it should be fine.

the general direction of the wind doesn't change much, it should be quite easy to park it out of the wind.

my rough calculations at 70 m/s (250 kph and 445 rpm) tip speed on a 3 m diameter fan spreading the 4.5 kg evenly gives me 7300 newtons per blade (740 Kg roughly) I could well be wrong, its been a while since I had to do any of this stuff.

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DaveP68
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Posted: 16 June 2018 at 8:16am | IP Logged Quote DaveP68

Yes Yahoo2's numbers are closer to the mark as missed some minor details, it's still 1000 kg's of blade force at 500 RPM! That's a lot of force in the grander scheme of things...

As I stated before profiling the Airfoil shape of the blades trailing edge more on the outer half section will get the weight down in the region that matters most.

The inner half of the blades can still have plenty of meat on them to maintain strength.
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BarkyJ
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Posted: 24 June 2018 at 7:57pm | IP Logged Quote BarkyJ

Evening All

Bit of an update. I have been pretty busy with work lately so not as far forward as I would like, but such is life.

I think I have the blades to an OK point to start playing with them now. They are all basically the same weight and shape, and once I mount them on the hub I will balance them to get them OK relative to each other and the mounting. This should happen in the next week or so.

Got the plate cut for the blades to bolt to, and the arms which bolt behind the blades, along with the thinner arms which bolt to the front on the blades. These arms all both to the central plate too, sandwiching the blades and go up about 400mm from the centre up each blade.

I got ring cut which will be welded to the bottom of the turrets pipe, which will have a 32T cog bolted to it. On the main pole, the motor will bolt to this, for rotating the turret, linked with a chain on the cogs. On the cog are 2 geartooth sensors, to allow quadrature like data to come off the teeth as the motor turns, to let me track exact position and direction of turn of the turret. Cables for the motor and sensors will enter the main pole, and run down to the controller along with the 2x 3 phase cables from the dual stators.

The geartooth sensors will track the position of the turret using the teeth on the cog, so my controller should always know where it is pointing, within a few degrees. If for some reason the turret moves without being driven (such as if the wind overpowers the motor brake - which hopefully won't happen), then the controller will still know where it is, and move it back accordingly. Still to implement all this stuff, but this is the idea. I am still toying with the idea of also putting up an electronic compass, so I can know where North is etc.

There will be 3 wires running up the pole into the turret which will connect to the RPS sensor also. I might run 4, so I can have a 2nd RPS sensor reading coming down too, so I can attempt to alarm if one of the sensors fails etc.

I hope to get the main pole in the next week, will get a 6m length, 1m will go into the ground into a formed hole in a slab of concrete, then 2.5m above the ground there will be a hinge for lowering the top half down to ground level. Then the top 2.5m will be above that obviously, with the turret on it. Just below blade level, I will put in some eyelets for the supporting cables, which will go out to support the whole thing. I will figure something out for raising it up again, like a smaller pole welded to the outside of the top section, so its possible to pull the top up vertical from the ground. Nothing new here.

I designed a PCB and got my first 'production version' of my controller built. I am using a 32bit 120Mhz controller now, well overkill, but will give me plenty of options and allow it to drive all the gear I have in my head for the future. Still testing the hardware, but so far so good.

I have a wind position sensor and wind direction sensor on its way, they should be here this week, which talk to the controller over RS485 comms. These will be mounted nearby and provide data to the controller as to the wind direction and speed, and allow my controller to position the turret using the motor system, into the wind, or at X degrees to the wind, or out of the wind when really windy, etc etc.

Being able to control the turret will also allow me to park it to allow it to be in the right position for lowering the windmill using the hinged pole, so the blades are in a favourable position.

I still have some thinking to do for 'what if' situations, but those will come in time.

I was just driving up the main road towards my house, which you can see partially from the main road, and just realised the place I am going to be putting the windmill is very visible from the main road. Just curious about regulation requirements here in New Zealand - does anyone know. Do you need to do something to get approval, or do you just go for it? This is not going into the grid, its an isolated system.

Cheers
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Posted: 24 June 2018 at 8:15pm | IP Logged Quote Warpspeed

BarkyJ wrote:
I am still toying with the idea of also putting up an electronic compass, so I can know where North is etc.
Cheers

The idea of an electronic compass had crossed my mind, but all those spinning magnets up there might confuse it a bit. But it might still work well enough to be useful.

An incremental encoder can certainly get lost due to any power outage, so it probably does need some automatic self correcting mechanism. The usual way is to have a third sensor that just resets the incremental position counter to some known specific reference direction. Could be due north, but it really does not matter.

If it gets lost, as soon as the third sensor produces a pulse, which it will do eventually, it resets everything to that exact known direction and its then corrected.

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BarkyJ
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Posted: 26 June 2018 at 3:13pm | IP Logged Quote BarkyJ

Yep, had thought of another sensor to reset everything, but it could be days for that to happen depending on the wind, so that is where the idea of the compass came in.

Noise is a factor for that which I have considered also. However, if noise is an issue then I could time samples to happen when there is no/low wind, and reset things then.

Anyway, there will be something to reset the quadrature to a known location, yep.

I may even get it to home periodically, say once a day, when wind is low. Dunno. Lots of possibilities.

The controller and motor etc will be on a 24V battery arrangement, and I have 20W of solar which will be keeping that charged. Ill monitor how that goes over the first few days and just ensure the solar is more than enough to keep it topped up, so hopefully power outages will be few and far between.
With the motor only doing small movements say once a minute, and it will only be on for < 5 seconds I would imagine, the power draw should not be that high at all. Motors will be PWM'ed to adjust the speed, so I will be able to tune in the appropriate speed to move the turret.

Cheers
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