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Gizmo
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Posted: 29 March 2009 at 8:56am | IP Logged Quote Gizmo

Well this is my first go at making a turbine with the extruded PVC blades.

I bought 3 lengths of 1 inch (25.4mm) steel exhaust pipe at 1300mm long, and 3 lengths of 22mm steel rod at 400mm long. The 22mm rod is a neat fit into the exhaust pipe ( id of 22.2mm ), and will strenghten the root end of the blade.
First I drilled 3 8mm holes into the exhasut pipe at 50mm, 200mm and 350mm from the end. These are so I can plug weld the tube and rod together.

I then tapped the 22mm rods into place.

and welded around the end and 3 plug holes. I also welded a nut as shown, you will see that this is used for later.

The plug welds were ground back and the whole thing painted with zinc coat.
Next day, I cut 3 lengths of the PVC blade, each one 1150mm long. These were slid over the steel tubes and pop rivited in place with 5 rivits each, 3 on front and 2 at back.

I used a wide head rivit, though I could have used normal rivits, just more of them.

The end caps/winglets were glued in place with liquid nails. I also screwed in a couple of small self tapping screws into the winglets incase the glue didn't hold. I figure if the winglet falls off, the open end of the blade would make a hell of a whistling noise as the turbine spun around, so I wanted to make sure this wouldnt happen.
I put the turbine together and did a quick test for balance, it was spot on.
Next day, fitted the new turbine to the 2 stator F&P windmill.

I've used this hub before when testing the fibreglass blades.

This is what the nuts were for. They stop the blades sliding out if the U-bolts work loose, and there is a security cable there, just in case.

And finally up in the air.

Initially I set the blades at 5deg, but after looking at Royal Fabrication's site where they tested similar blades, I changed this to 10deg to keep the RPM down.

The turbine starts up easily, and so far they have been silent. Will post more in a couple of days.

Glenn

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Posted: 05 April 2009 at 7:12am | IP Logged Quote Gizmo

This weekend I took the windmill down for some work. It had developed a squeek, one of the F&P hubs was rubbing against the stator, a bit of a problem with dual stator conversions, and I also wanted to paint the blades.

I did manage to record some video of it running today, the wind has been non-existant the last week, I've only seen the mill running a couple of times. The video can bee seen here....
http://www.youtube.com/watch?v=tWnAopJj4Qk
You'll notice there is only light wind, but I was still getting 1 to 2 amps during the day. If you listen you can hear the stator squeek.

One big plus, the turbine runs silent. I even unloaded it to let it speed up and I could barley hear it.

Glenn

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Posted: 05 April 2009 at 8:52pm | IP Logged Quote brucedownunder2

Hi Crew, Yes, I've noticed that the "scratching" sound is prevelant in the dual set-up.
I'm wondering if it's because we are bolting the mill down on the plastic hub portion of the rotor,just guessing.

I generally take the rotor off and look around the magnets and the ends of the stator fingers for rubbing brightness,then gently grind these off --but,, you have to mark the position of the rotor BEFORE removing it ,,so you can re-install at that same location.

The humm you hear is different,it's not rubbing,it's the harmomics from certain rotors and at certain rpm,generally on the start and before stopping.

Have fun, Bruce

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Posted: 06 April 2009 at 2:00am | IP Logged Quote vasi

I'm curious to see if non-twisted blades performs better in low wind areas...

And what happens in a storm...

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Posted: 25 April 2009 at 4:01pm | IP Logged Quote domwild

Glenn,

Are you using an angle measuring dial, cost app. $38 for your setting of the pitch?

Thanks.


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Posted: 25 April 2009 at 4:06pm | IP Logged Quote domwild

And another thing: Would it be worthwhile to stick with 25.4 mm stainless steel and no internal rod to reduce the inertia of the assembly? A six metre length of 1.2 mm wall thickness is about $48 or $8 per metre.

Regards,


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Posted: 25 April 2009 at 6:49pm | IP Logged Quote Gizmo

Hi Dom

I made my own angle dial from a protractor, length of flat bar and a weight.



With the turbine mounted on the windmill or a stand, I first check the angle of the hub itself, just in case its not straight up and down. If its out, I'll add its reading to the readings at the blades. Then I rotate the turbine to get each blade level in turn, and use the dial to take a reading from the underside of the blades. If you put a straight edge under the blade, the reading is 3.2 degrees from the blades 0 angle of attack. So if I want a 10 degree angle of attack, I back off the U bolts and turn the blade to 13.2 degrees.


Yes stainless is better than mild steel for the tube, it wont rust. But you MUST still use the solid rod from the blade root to at least 200 to 300mm into the blade itself. There is a lot of force at the root of the blade, where the 1 inch tube mounts to your hub. Stick a 1 meter length of 1 inch tube in a vice at one end, and stand on it about half way along. It will break. This is the same sort of force the blade can expierence in a storm. Timber blades will bend and recover to absorb the strain, but when they break they shatter into smaller bits. These PVC blades wont bend and recover, they will just bend and break off, and stay in one piece as they head towards your house. So we need to make them strong where they are going to break, at the blade mount. The rod also means the U-bolts wont crush the tube and work loose.

The extra inertia from the extra weight would have very very little effect on the turbines performance, the hub itself is way heavier. Its just not worth making a weak blade for an extra watt or two on a gusty day.

Glenn

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Posted: 26 April 2009 at 6:40pm | IP Logged Quote domwild

Thanks, Glenn. Clever design of yours of the protractor!



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Posted: 28 April 2009 at 12:49pm | IP Logged Quote domwild

Glenn,

1. The sequence of building intrigues me. Can you pop rivet the prop to the 25.4 mm tube AFTER the 22mm rod has been inserted? Is there enough gap between round and tube to allow for a rivet head to be formed?

2. Six mm mild steel for the hub parts; is four or five mm good enough for a single F&P or not?

3. Any changes to your existing DFX files for the extruded blades or is this the final design?

4. What sort of software allows me to view the unzipped version of those DFX files? Is it free for download?

Regards,



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Posted: 28 April 2009 at 1:09pm | IP Logged Quote Gizmo

Hi Dom

1. Yes, its a blind hole. The rivet grabs the side wall of the hole instead of the back ( inside surface ) of the tube, it will hold just fine. The rivets main job is to stop the blade rotating around or sliding off the tube, there is no force trying to pull the rivet out.

2. Depends on how big your turbine is. A small turbine under 2 meters might get away with 4mm. Flat steel bends easier than box section or anything triangulated, so you need to go a bit thicker.

3, Not sure what DXF files you mean. The Hub?

4. Any CAD file can open a DXF file. A laser/waterjet shop will have the software. A free CAD file is CadStd http://www.cadstd.com/

Glenn

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Posted: 29 April 2009 at 8:31pm | IP Logged Quote domwild

Thanks, Glenn. Yes, I mean the zipped Smartdrive DXF file listed on the page with the link to order form; or is it on the order form?

Have just ordered the blades.

Thanks.


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Posted: 03 May 2009 at 2:11pm | IP Logged Quote domwild

Glenn,

Measuring the internal dia. of the short sample sent to me from the US I noticed it has an ID of 23mm max. When it is expanded to 25.4mm after pushing the exhaust pipe in, doesn't it mess up the profile? Does it go in easily enough?

Thanks.


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