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16 footer update
By Hilltopgrange, Section Wind Posted on Sun Jun 21, 2009 at 10:55:01 PM MST
Magnets with a capital T part 2

Hi Guys,
time for a progress report on the 16 foot turbine I am currently playing with. My last post on this machine can be found here http://www.fieldlines.com/story/2009/5/23/135436/243 Magnets with a capital T
Well a lot has happened since the last posting. the metal work is now complete and ready to go on the tower, just waiting for the wind to stop blowing

The yaw tube was originally a hydraulic cylinder removed from an old JCB and the stub axle and flange are from the front axle on an old series Land Rover. I try to recycle as much as possible from my ever growing junk pile

The tail boom is 8ft long and follows the design from the Dans book for the 17 footer, the alternator is tilted back 5deg again all pretty standard stuff. I did however deviate from the design with the offset, I decided to go with a full 6% 11.5 inches. I pondered hard over the offset I studied many old posts on the subject I eventually decided that to much is better than to little and went with the full 6%. I may need to play with the tail angle/area to track the wind correctly and also with the weight to control the furling point. One other change to the design is a positive tail stop with a rubber bumper, this stop is made from 1.5 inch box section, it will also serve as a lifting point for hoisting up the tower but its main purpose is to prevent a blade strike when fully furled.

The trickiest bit to figure was the tail vane area as there are so many variables and conflicting examples so I decided to just guestimate it and tweak it later. I settled on a vane 6ft x 4ft of ½"ply
The stator is 3 phase 48v each coil has 40 turns of 2 in hand 1.6mm, I connected a set of bridge rectifiers and spun her up ,cut in at 48v was 109 rpm , right on target for a 16ft prop.

The tower this machine is going to sit on is currently flying a 12 footer it's the one behind the house
The 12ft machine is coming down and I will be fitting a new section that will give the tower an extra 10ft and anchor points for additional guys. The new section is 4" dia heavy wall galv tube it is 20ft long but 10ft will be inserted into the tower, the end of the tube is plated with ½" plate and it will have a ½" thick brass disc/washer as a bearing. I have also installed grease nipples on all the moving parts

The turbine at the front of the house is a 10 footer on a 35ft tower it and its tower are moving down the hill to run the lights and pumps for the Polly tunnel and garden features. I will then build a new 60ft free standing tower for the 12 ft machine it will be sited in place of the old 10 footer.... I think ...or at least that is the plan.
So that's the progress so far, all we need now is some decent weather!
Russell

16 footer update | 11 comments (11 topical)

Re: 16 footer update (3.00 / 0) (#1)
by SparWeb on Mon Jun 22, 2009 at 01:20:24 PM MST

What a beautiful place to live, if a bit challenging for wind power. A 60foot tower could turn the 12-foot windmill into a better performer than the 17-foot mill!

I have tried compiling a comparison of windmills with an eye to comparing proportions, just to see if relative proportions of diameter/offset/tail length/tail size can be used consistently, and what happens if they are not. The 6'x4' tail sounds like a good start. You have slightly more offset than needed, by my calculations, too, so I agree with your conservative estimate.

Do you mind if I add info from your postings to my list?

Does the upper arm or lower arm of the tail strike the bumper first?
Steven Fahey

Re: 16 footer update (3.00 / 0) (#2)
by SDSUMetalHead on Mon Jun 22, 2009 at 01:33:14 PM MST

SparWeb...do you have your findings posted somewhere. I would be very interested in seeing the results. Great looking stuff Russell! I am extremely jealous.
SDSU MetalHead
[ Parent ]

Re: 16 footer update (3.00 / 0) (#3)
by SparWeb on Mon Jun 22, 2009 at 01:36:22 PM MST

Looks like you're on-line as I'm typing, here.
Still saving the spreadsheet...

Steven Fahey
[ Parent ]

Re: 16 footer update (3.00 / 0) (#4)
by SparWeb on Mon Jun 22, 2009 at 01:46:00 PM MST

Here it is:

http://www3.telus.net/faheydumas/Wind_Turbine/Forum/Wind_Turbine_Comparison.htm
Steven Fahey
[ Parent ]

Re: 16 footer update (3.00 / 0) (#7)
by dlenox on Tue Jun 23, 2009 at 02:00:45 PM MST

Russell,

I would be very interested to know how this offset works for you.

I have a 17'er and am currently using 9-1/2" offset and have considered adding about 1-1/2 to 2" which you are in the ballpark with.

What sort of air gap do you have between the magnet surfaces?

Dan Lenox

[ Parent ]

Re: 16 footer update (3.00 / 0) (#9)
by Hilltopgrange on Tue Jun 23, 2009 at 06:27:52 PM MST

Hi Dan,
no problem I will post updates with the results good or bad lol.
The stator is 1/2 with a 1/16 clearance each side giving a total of 5/8. My magnets are the standard 2x1x1/2 with 2 per pole mounted in a T shape. I am in a very high wind area and my machines take a real beating so if it fails to furl it will self destruct. I have had a few problems with furling in the past so this time I decided to go with extra offset and furl to the other side as is the latest trend. We will soon see if it works or not.
Regards Russell

[ Parent ]

Re: 16 footer update (3.00 / 0) (#10)
by Dave B on Tue Jun 23, 2009 at 06:57:36 PM MST

Russell,

What direction will your blades turn when looking from upwind directly at your blade face ? A couple of comments for what it's worth. 1/16" from your magnets to stator is close (in my opinion) for 16' blades. Rotors do flex, stator mounts do flex while wild forces are exerted when yawing at speed and under load. Especially hard on the machine flexing parts is slamming hard to the home stop from fully furled with a reverse wind direction. After a time there will also be some wear in your bearing(s) besides. If you fully furl at a low enough RPM you may not experience any problems for quite a while. Just some thoughts after tearing mine completly down after a year. Good luck with your machine, it looks great. Dave B.

[ Parent ]

Re: 16 footer update (3.00 / 0) (#11)
by Hilltopgrange on Tue Jun 23, 2009 at 07:22:52 PM MST

Hi Dave
I haven`t carved the blades yet but they will be CW rotation. I can add another 1/16 -1/18 of clearance on the final assembly better safe than sorry!

I hope you get yours back up in the air asap

Thanks for the advice

Regards Russell

[ Parent ]

Re: 16 footer update (3.00 / 0) (#5)
by Hilltopgrange on Mon Jun 22, 2009 at 04:04:02 PM MST

Hi Steven thanks for the comments. You can use the details as you wish,thanks for asking some folk just take lol. If you need any more info just let me know.

The tail stop is at the same angle as the tail so that both tubes of the tail strike the bumper together.

The forecast is looking good for Wednesday and Thursday so I hope to get raised!

Thanks again guys for the comments

Russell

[ Parent ]

Re: 16 footer update (3.00 / 0) (#6)
by Ungrounded Lightning Rod on Mon Jun 22, 2009 at 09:11:49 PM MST

That thin piece of rubber strikes me as having very little give to absorb the energy of a swinging boom. I'd find two of the pointy bumpers that are used on automotive suspensions that are about an inch high and decelerate the boom over much of that inch. That will keep it from kinking if the wind suddenly whips around.

Similarly, I'd put a bumper for full-extension on the other side of the boom, rather than relying on the hinge cutaway:

- Look at the distance out from the pivot to the center of the tail vane. Call this "A".
- Look at the distance from the center of the tail pivot to the area where the cutaway strikes the supporting plate. Call this "B".
- Figure the side force on that tail vane when the wind is trying to yaw the mill after a sudden shift. Call this f.

The force big "F" on the hinge cutaway is F = f * A / B.

Now think about the hammering when you're furled in a storm and an eddy makes the wind at the tail suddenly shift, blowing the folded tail suddenly out toward that fully-extended stop. The tail gets moving along fast, with all the mass of that boom and the vane moving. And it all comes down on that cutaway with that A/B multiplier for the inertia of the vane and 1/2 A/B for the inertia of the tail boom. Ouch!

I know people have gotten away with this in the past. But I'd really rather have the boom come down on another energy-absorbing bumper a foot or two out from the hinge than come down on that cutaway.

Re: 16 footer update (3.00 / 0) (#8)
by Hilltopgrange on Tue Jun 23, 2009 at 06:12:38 PM MST

Hi ULR thanks for your comments,
you have raised a couple of interesting points! I share your concerns about the cut out tail stop as is "normally" used. I used very heavy walled tube on the cut out tube and reinforced it as is the norm but I still feel it is a problem waiting to happen. This is the 7th machine I have built and I have never had one break yet but they do show signs of wear after time. The tail assembly is just one large heavy lever bearing down with considerable force on a very small area at, some point something is going to give.

I think I have some land rover axle bump stops tucked away somewhere that I could possibly use, I will have a rummage tomorrow and see what I can find. It actually did occur to me when I was fitting the fully furled stop but I decided to keep it simple (unusual for me) and follow the herd lol. I also considered a simple chain from the outer most edge of the alternator H section to the middle of the tail boom but decided against it just in case the chain was to break at the tail thus allowing the chain to get into the blades.

The rubber bump strip that is already fitted is more substantial than it looks in the pic it is almost ½ thick with a hollow section and is surprisingly effective, I think it should be ok as it doesn't get hit with the same sort of violence as the cut out stop. If It does fail its an easy fix or mod compared to the cut out.

Thanks again for your input and the heads up I will let you know how it works out

Regards Russell

[ Parent ]

16 footer update | 11 comments (11 topical)

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