| T O P I C R E V I E W |
| Tim L |
Posted - 13/05/2008 : 17:35:44
OK, I got worried about my wooden 9ft prop (with reason too - after the gales earlier on I took a look and the blades were split along their length, not good at all for 600 RPM potential javelins) so I sent off to CMSMagnetics in Texas for a set of 10ft 6in reinforced fibreglass blades plus hub.
They arrived a couple of weeks ago and, while my friendly local engineering shop is making an adaptor to fit the very substantial hub to my Renewable Components-sourced 1KW stepper motor, have taken a gander at the blades themselves.
While they all balance at the same half-way point, the blades weigh 3042, 3055 and 3020 grams - advice please - should I shave the heavier ones down, while still keeping the same half-way balance point of course, or is that weight variation within normal vibration limits when the prop is dong a few hundred RPM? My inclination is to shave them, but they are sold as "balanced" and I'd rather not mess with them if I can help it - too much chance of inadvertently knackering them.
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| 15 L A T E S T R E P L I E S (Newest First) |
| Tim L |
Posted - 27/05/2008 : 11:41:48
Hi gholt
Thanks for the interest and the compliment!
The blades are very substantial and as Ghurd pointed out the difference is only about 1% so it might not matter too much, but I'm a bit of a worrier with big weights and high RPM, especially in my current urban setting.
The motor is one of the few that Renewable Components were selling off cheap (I got mine for £47), the ones that are said to cog badly, and yes it does cog a bit - but not enough to stop my very first attempt with wooden blades from packing a big punch, OK it took a gale to do it but it utterly overwhelmed my 2 little parallel 12V car batteries and 300W of divert load and poked to 30V and nearly 30A at one point.
It was a bit of a concern - the batteries were getting warm and going "blup....blup...blup". I hadn't expected that, the batts are only there to clamp the voltage, everything extra once they were charged was supposed to be eaten by the test divert load (of a couple of cheap 3KW electric radiators in parallel). It's now set for 24V so the divert load should have twice the capacity, and I've also now got a 24V 1KW inverter wired up and ready to go if the low voltage dumps can't eat all the power.
It's all a temporary setup, when I move I'll either make the divert from a couple of 600W 24V immersion heater elements in the hot water tank, or modify my 1KW inverter to soft-start and run a standard domestic immersion heater off it.
I'd like to think that the cogging effect will mean I don't wear out the bearings (Gordon at Renewable Components said though that the bearings were standard and easily replaced if necessary) by idly spinning in faint winds that wouldn't get it up to charging speed anyway, and that when a good wind comes along they'll start spinning like they did before.
The blades are supposed to be able to deliver well over a kilowatt - hitting 1KW at 18mph and peaking at 1.8KW, though what with the motor cogging and my low tower in dirty air I'm not too worried about that, especially as the TSR drops from 10 unloaded to 6 under heavy load; if all goes well, after I've moved and when this motor wears out I'll go for one of Gordon's 2.2KW units - both the axle and prop mountings look exactly the same as my motor so with any luck it would be a straight swap-out.
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| gholt |
Posted - 27/05/2008 : 03:55:06
Hello Tim L,
Your photos and blog are very interesting. I've been considering a set of these blades myself, although I'm a bit surprised at the differing weights and the approach they used to "balance" them. I'm glad you brought this up. If I do make this purchase, I'll approach the balancing by the addition of surface coatings as previously mentioned in this thread, and make the hub mounting lengths all the same.
Tell us more about this 1KW stepper motor. What's it's origin?
I liked your mobile RE cart concept - pretty sweet little setup.
G. |
| Tim L |
Posted - 26/05/2008 : 14:32:09
Aha.
The 3 Hub mounting points for this 10ft 6in prop were not all exactly the same distance from the shaft. Magnifique! - they are sold as balanced - looks like the hub is part of it.
No.2 is 1mm further out than no.1 and the no.3 is 1.5mm further out than no.1. So I mounted the 3055g blade at position 1, 3042g blade at position 2 and 3020g blade at position 3.
I think I've got it!
I reinstated the 4 inch fencepost tower made of 2 posts. Bottom one carries all the crossbracing, top one is fixed to bottom one with two big 20mm (yes, shipbuilding-size 20mm diameter) x 220mm high tensile bolts with load-spreading washers. Using the bottom bolt as the pivot and fitting the winch to the top of the base fencepost let me crank it all up pretty easily, despite the weight.
Genny fixed pointing West; now all I need are some Westerlies.
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| gholt |
Posted - 16/05/2008 : 05:20:01
Hello Tim L,
The prop can be suspended in two orientations for balancing, either in the vertical or horizontal planes. Typically the blades are mounted on their hub as described by Ben above prior to attempting any balancing act. Personally, I like the horizontal suspension on a suitable cord through the hub central shaft hole. When suspended in this manner the blades talk to you very readily about which one is light or heavy.
It's much easier/safer to add weight than to remove it. In your case we're talking about 35 grams to be added to the lightest blade and it might surprise you to know this is just a few brush strokes of epoxy enamel. One of the advantages of this approach is not adding materials that can fly off later as shrapnel and then you're not knowing when the unit will shake itself into oblivion. Adding weight with this approach is safer especially for fiberglass because you'll not be endangering the fiberglass material by cutting into it's surface and the addition of the covering coat merely serves to protect it further rather than to open up the surface of the fiberglass to induced weathering - if we can call it that.
Let us know of your process and how it turns out for you, I'm sure we're all ears ...
G. |
| Tim L |
Posted - 15/05/2008 : 16:37:06
Got the adaptor today, and am now all set to redo the tower, slap it together, and winch it up. Probably this weekend, if it's not raining too hard.
The engineering shop has done a very good job.
The original genny fitting is rather soft alloy, they recreated it in steel, with a big 30mm dia bolt poking out, and counterbored to make a location for the hub prong which slides into the counterbore to take the weight. There's a transverse hole to take a spring pin (though I might use a bolt instead) to transmit the torque, and the nut at the end is safetied with a split pin.
The hub had a tapered hole down the centre and a UNC or UNF thread at the end, they cut the thread off, bored the hole out and fitted a length of steel tube in there with a flat on the prong so it only slides into the adaptor one way.
Have added a pic to my blog at www.mostlydiywindturbine.blogspot.com if anyone's interested.
You'll have gathered by now that I'm a great fan of Victorian overengineering....
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| Tim L |
Posted - 15/05/2008 : 10:58:02
Indeed it is, holding bottle of champagne in hand - but also wearing tin helmet and kevlar jockstrap as well, just in case.
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| gotwind |
Posted - 14/05/2008 : 22:34:25
As advised by ghurd and Hef above,
It's a case of 'suck it and see'
Ben. |
| Hefhoover |
Posted - 14/05/2008 : 21:14:34
Are you a man or a mouse? Do like Donnie did and stick it on an outboard lathe at 800rpm, that'll tell you how good the balance is!!
(I'd have loved to see that......on video!) Hef ;-) |
| ghurd |
Posted - 14/05/2008 : 20:49:43
You think WAY too much! I mean that in a good way.
I used to do that too, but I gave up.
IE: One blade is too heavy. Remove it from the hub, etc. Lighten it by 33% of what you spent a month calculating it was too heavy by.
Then replace it and find out it is now 80% lighter than you calculated it was too heavy by.
Repeat, until my blades were all saw dust in the skip.
The act of removing and replacing a single blade, "only dicking with one variable at a time", changes every other variable.
Yes, that 230RPM is barely turning and "super~slow". Until you stand near it!
10 foot 6" and 230RPM is... frankly... "Pee your/my/their pants" frightening!
If the fence post tower has a slight extension that is not as solid as granite, an imbalance should be easy to see (maybe even hear) at maybe 60 or 90 RPM.
I expect it will have vibrations due to cleaner wind on the top half.
Isn't minced carp a delicacy in some regions?
Maybe it could be approved as a "wind powered food processor"? 
(google "opel 92 pound carp" and it seems reasonable!)
You are planning every detail. I am sure you will be completely happy, with a tweak or 2... Everything needs a tweak.
G-
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| Tim L |
Posted - 14/05/2008 : 19:33:37
Thanks Ghurd
Hoo boy, am looking forward to flying the thing. On the sound engineering principle of only dicking with one variable at a time, I may well revert to the tried and tested fencepost tower and see how that does with the new prop, rather than change both prop and tower at the same time.
Hope it won't be too slow though, I need 230 RPM to get to 24V, but one of the major factors in my choosing this prop is the TSR of 10 unloaded ranging down to 6 heavy load. it's got to be better than my own crappy wooden effort.
My concern about the proposed UK planning regs is that the planners might not have a brain cell and even if the tower is under 11m, and mine will only be 6 or at most 7 m, might still require 36ft clear space. My tower is 4m away from my Western boundary, where all the big winds come from - I did that so even if it does fall over in a gale, it wouldn't go into next door. In fact it's placed so it would fall straight into the 16ft by 8ft concrete Koi pond and mince the fish......which is preferable to mincing a downwind neighbour, even my own drugtastic tosser of a neighbour.
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| ghurd |
Posted - 14/05/2008 : 18:54:19
I sure wouldn't worry about it much at this point.
I'd be thrilled with about 1%!
By the time they get cleaned up they will change anyway. Bit extra sanding on the heavy one?
Then paint can change it a bit more. Maybe a hair extra paint on the light ones?
Aluminum tape on the leading edges? Maybe 2 layers thick on the light one?
Then the hub (always my problem), and adaptor.
What if the blade holes are a 1/10mm one direction, and the shaft hole is 1/10mm the other direction? Or if one hole is 1/10 of a degree off from where it should be.
Same with the adaptor.
I bet this will fix it...
Something that big and slow will be easy to tell if it isn't balanced.
If it isn't balanced at the end, switch 2 blades. Still not balanced? Switch 2 blades, including the one that was not switched the first time. Then the one that wasn't switched the 2nd time. (PITA, but it works Very well for me)
Might google 'balancing a ceiling fan' or something like that for better instructions.
Might have to rotate the adaptor related to the hub?
I don't think it will be any problem.
Yea. I make my own hubs.
No. I'm not good at getting the holes where they should be.
G-
PS- Might want to get it flying quick? Post some photos. Then "repair" things such balance as needed?
US would have grandfather laws about not making one be removed, if it is pre-existing.
Hmmm... 11M high, plus 1M radius (2M dia), equals 12M to the neighbor's dirt.
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| Tim L |
Posted - 14/05/2008 : 17:13:18
Capt
Good point about trying it out first! I found their balance points by laying them side by side on a wooden dowel and slowly rolling the dowel across the floor, and they all seesawed simultaneously. I did that 3 times and it was quite reproducible, but you're right, and I completely take your point about only needing a couple of mm difference.
they're pretty substantial pieces, and so's the steel hub, but they do need a bit of cleaning up. Take a look at www.mostlydiywindturbine.blogspot.com to see them.
Cost was $100 USD plus another $100 for shipping to UK (it apparently should have been more but they made a mistake on the shipping weight). CMS had tremendous trouble trying to change my GB £ cheque, their bank wanted to charge them over $50 to do it, so I found a way to pay in US$ instead. If you're looking to get a set, I strongly recommend you pay them in US$. It only took a few weeks for them to arrive.
So now the head unit will have 12Kg of stepper motor and mounting, a 4Kg hub, and another 9Kg of blades, a total of 25Kg or so. Though I've bought a little 400Kg winch to tilt the thing up, am starting to wonder whether the scaffolding pole is strong enough for the job - I might revert to making the tower from 4 inch fencepost. Last thing I want to happen is for the pole to bend in a gale and the spinning blades to smash themselves to pieces against it!.
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| Capt Slog |
Posted - 14/05/2008 : 11:37:02
If they are sold as balanced, don't do anything with them untill you can get them back on a hub and see them turning.
Whilst it's true that you would like to see them all the same weight it might not be a problem, it could be how that weight is distributed. I know you said that "they all balance at the same halfway point", but how accurate was that? You would only have to be out by a millimeter or two to compensate for the any uneven weight distribution.
I'm interested to know what you paid for them, delivery, how they look etc.
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| Tim L |
Posted - 13/05/2008 : 21:36:20
Ben
I wondered about adding weights to the hub but while that would balance the prop statically, wouldn't it throw off dynamic balance, in that the blade units as a whole - while they would weigh the same in total - would no longer balance at the same half-way point, and so have different angular momentum when rotating. I'll try balancing it statically as suggested and see how that does. If it then plays up when spinning, I reckon I might try some light glasspapering - the material to be removed would only be a few grams distributed equally along the whole blade length, and i might get away with it. As received, both the leading and training edges are a bit blunt and messy anyway, and the tips could do with some reshaping, and I had intended to clean up and sharpen them very slightly in any case. Depends on how much resin facing material there is to play with before I start sanding glass, I suppose. On the other hand, I would only need to take off a total of 22 and 35 grams of material from each blade - 11 1/2 g from windward and leeward sides on one blade, and 17 1/2 g from each side on the other blade, so it might not be a definite death sentence.
PS: the 10 ft 6 in I quoted is the prop diameter, not the length of each blade.
PPS: the latest I've seen on planning regs amendment proposals is that max dia is 2m, max height is 11m - hooray - but the sand in the gearbox is that the installation must be 12m away from the nearest boundary, and that knackers my back garden for a start. How many of us have a clear circle of 36ft to mount in?
Note: A YouTube Video Is Not Necessarily Proof Of Anything At All
www.youtube.com/watch?v=UpNp4l0qyY0 |
| gotwind |
Posted - 13/05/2008 : 20:44:42
Hi Tim.
Rather than removing material from the heavier blades, (it might be tricky with fibre glass anyway).
I would add weight to the lighter blades, in the form of weights attached to the hub bolts (very securly).
And balance whilst mounted vertically on a good bearing.
From Navitron site:
Balance the Blades -
There are various methods of balancing.
First attach the blades to the hub. Before tightening, whilst there is still some movement available, ensure that the tips of each blade is the same distance from the centre of the hub. Also ensure that the distance between each blade tip and the next is the same (This ensures that the blades are mounted at exactly 120degrees. Once the blades are aligned, tighten the bolts, taking care not to disturb the position of the blades whilst doing so. The blades can now be balanced by mounting the blades on the turbine in windless conditions (may need to be done indoors, if it is windy). Position one blade at the 3 o'clock position. Hang a suitable weight (eg bent piece of lead or a weight attached to a large hook) over the blade close to the hub. Unless the weight is particularly heavy, it should not move. Gradually move the weight outwards, until the blade just starts to move. Mark the position on the blade. Repeat for the other two blades. If the positions are all the same, then the hub is in balance. If one blade mark is further out from the hub than the others, then this blade is lighter, and more weight needs to be added. You can adjust the balance either by adding weight to the hub (e.g. sections of lead or steel secured by the bolts). Alternatively, you can bore holes in the tip of the blades or bore holes, and epoxy small roles of lead into the holes. Ensure that holes are sealed after use, to prevent water ingress into blade (which will cause blade to become out-of-balance).
Ben. |
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