Power Furling

[kitestrings]

I replaced the dyneema line recently on our furling actuator.  It had gotten chafed where it was rubbed on the sharp sides of the pivoting sheave.  I also noticed that UV and weather also were starting to effect flexibility some, though this was a lesser concern.


I also replaced the pivoting pulley, but I have not been happy with the nylon sheave for this application.  It's just not quite heavy enough for the long-haul.  You can see where it had worn, and elongated the hole considerably.  I've fitted the one I replaced with a steel sheave that has a bearing.  This one is rated for about 600# IIRC.


I still need to cut the bolt to length.  I was trying to keep the smooth shank of the bolt in contact with the inner race, rather than the treaded portion, thus the longer bolt.


The pull is hardest right near the end of the motion, when it is nearly fully furled, and this is where it tends to rub.  I since have filed the sharp edges of the pulley housing.  And, when we're furled and riding out a rough storm, or just no longer needing the power, the wind is constantly working the tension on the line.

It was beautiful weather when I replaced the line.  Here is a pic from this morning.  We just got a late snow that's dropped a couple inches so far.


Now I just have to swap them out.  For anyone not familiar, here is a thread on the power furling.  It has worked really, really well for us:
https://www.fieldlines.com/index.php/topic,149230.msg1040709.html#msg1040709

[SparWeb]

I wouldn't want to climb a tower in that weather!

That looks like  the kind of sheave that allows you to tighten the bolt to proper torque because it runs on a bearing.

That's a textbook example of stress creep, in the plastic ID.

Is there a 50/50 solution, where you can get a nylon/delrin sheave with a mounted bearing in it?  That would be gentler on the dyneema line, and avoid the stress creep problem.  Not that I think that galvanized steel sheave won't be OK, but comparing the wear on the line VS. the nylon sheave, which one wears out faster?

[kitestrings]

Yes, so this one was the closest stock size that I could find, without having something custom made.  They (Block Division is the source) also allow you to spec the bushing ID, which was a plus in this case.  The sheave is cold-rolled bar stock that's zinc electro plated.  I think this will work fine, even as is, but I'm wondering if priming and painting might be good to do?

I put washer/shims to allow the bolt to be tightened against the inner bushing.

Stress creep.  It vaguely registers from "Statics and Strengths of Materials" with Professor Levine (1979?).  Question: on CU/AL electrical compression terminations, they talk about "cold-flow", I think it is called.  As I understand it, ideally you want to recheck/torque as things continue to form/deform for a bit.  Is this the same thing, or unique to wire; perhaps only stranded wire?

The line wear is almost entirely from the stamped housing of the pivoting pulley assembly.  When the line is pulled to the side, it can rub a bit, as the thing pivots around.  I think this has largely solved by just a bit of hand filing to round out those edges.

[Mary B]

Stress creep in wire was a problem with aluminum, quite a few trailer houses burned down before they banned the use of it to wire them.

[SparWeb]

The line wear is almost entirely from the stamped housing of the pivoting pulley assembly. 

OK>  wear on the dyneema line has nothing to do with the wear in the throat of the sheave.  Then your problem is solved.

You guessed right. Stress creep is probably the same thing as (or very similar to) cold flow that you referred to.  Can happen in tension or compression.  The material "flows" very slowly, over the course of hours/days/months into a new shape while the stress is maintained.  In your case, the ID of the nylon sheave seems to have been given a permanent set after tension stayed on the cord for a long time, and probably on a hot day.  Exactly what your prof. was talking about.

[SparWeb]

If you were to do it again, would you choose to put the furling cable through the center of the mast? 
Or would you consider the external "clutch" style now?

[kitestrings]

"Clutch style", please explain, I guess I don't recall seeing this (or I've forgotten).

I don't think I'd hesitate to do it this way again.  All things considered, it is pretty simple and dependable.  Periodically we have to untwist the cable, and line, but it is easy to do - I probably do it every couple months or so...

I think bigrockcandy was considering a similar, but wireless approach.  This might be an improvement.  I suppose a wireless control might also allow the actuator to be integrated where the pull line could be eliminated.  The trade off IMO is that anytime you put something up on the tower that could go on the ground, or in the house, you may have solved one problem, but created others.

PhilM on The Back Shed had a pretty slick funnel-shaped rope guide for a manual furling line on one of his turbines.

[kitestrings]

re: AL wire.  I had thought much of the issue was linked to incompatible terminations.  Is that not true?  They sure use a lot of AL wire in other applications (URD, transmission, etc.).

[Mary B]

Yes it was AL to Brass or copper terminations that were failing, getting hot, and starting manufactured homes on fire. This was before the use of antioxidant pastes and recommendations to re-torque terminals every year which in a house could be an expensive cost(pull out every outlet and light socket and switch to tighten screws...) and many homeowners were not capable of it and they couldn't afford to hire someone so fires would still happen.

[SparWeb]

Deep deep rabbit hole there.  The terminations getting hot is just one step in the chain of events.  Once heated, the copper lug will return to its original size, within a few hundredths of a thousandth of an inch.  The aluminum, however, softened during the heating, flowed a little bit, so once it cools it's a few tenths of a thousandth of an inch smaller.  The clamping pressure lets off a bit.  Do that often enough (eg. air conditioner, refrigerator, stove power on/off cycle) and it's going to get looser every time.  Also, as it gets looser, the lower pressure allows the resistance in the connection to increase.  Higher resistance puts more heat in the connection, making it hotter the next time.  Slippery slope.

The clutch connection I referred to is the mechanical means to allow pulling on the cable but letting it turn freely at other times.  In that way, it's like the clutch in an auto, except it works in the opposite way.  The car's clutch is normally closed, the WT's clutch is normally open.  The car's clutch transmits torque, the WT's clutch transmits axial force. I've seen a variety of these actuators on wind turbines, and I put them in a general category that I refer to as the "clutch" style.  Thanks for referring to FillM's example of a cable up the center of the tube like yours.  I'd forgotten about that one, and you gave me a bit of a stroll down memory lane.  I'd contributed a bit to those discussion back in 2009/2010.  Ah, but I was so much older then.

Manual furling is a feature that I want, but I'm still trying to balance it with my other desires to have a very simple power cable. For now that means a pendant cable with no slip-rings, in my mind.  But I can't square that with a power furling cable that also passes through the inside of the tube - they would tangle.  So I am still considering the clutch style furling actuator that works as a sliding sleeve outside the tube.  If I decide I don't want that, then a cable actuator such as yours will be the order.

Another deep rabbit hole...  I'm thinking about the next tower I'm going to build.  I have had it with the tower I have.  The power cable is twisted up again so tightly that it will soon prevent yawing.  I made some fatal mistakes when I first built that tower and the fatal moment is almost here, and unavoidable.  Enough about my story.  If I want to tell it, I'll start a new post on the subject.  Right now I haven't even decided what to do.

[kitestrings]

Hmm.  Yes, it seems there are trade-offs with every choice.  Bigrockcandy has a furling design as you've described, with a sleeve on the outside of the tube.

One of the obstacles is that we have a tail where the default position is open, unfurled... but ideally, I suppose, the natural position, and fail-safe would be closed, furled, and we'd counteract that force only when we want to run.

I hope you are able to resolve the tower issue.

[bigrockcandymountain]

Yep I hope you try out the "pull to turn on" system.  I'm quite happy with my manual furling, but it definitely isn't perfect. 

I have been letting my turbine run in some pretty bad winds lately, just to see how it behaves.  It seems like it would survive prettt much anything.  I still like the option to shut it down though, just to be safe. 

I used aluminum cable for the underground run down the hill here.  I used the paste and torqued everything.  Maybe I should check stuff once in awhile.  I thought the problem with aluminum was all dissimilar metal corrosion.  Sounds like there is more to it than that. 

[kitestrings]

One more tweak


My grandfather always used to put a piece of leather over a latch or padlock.  It seemed to be pretty effect

[SparWeb]

Leather pants.   Very....  "Harley Davidson"

[Mary B]

Good leathers saved my butt when a friend laid her bike down to avoid a deer. Slid 75 feet. Beat hitting a deer at 60mph! Wore almost through to my hands, hip one side I was sliding on, and elbow one side wore through giving me a patch of road rash. She hollered going down and wham... sliding with one leg trapped under the bike. The saddle bags saved that leg because they took most of the damage. We were headed down to one of my fishing spots in the river valley late October... dumb buck was not watching anything but the doe who went across the road in front of him.

[SparWeb]

I hear enough stories about getting the bike laid down for a crash, but how often does that maneuver succeed?  Friend of mine who bikes a lot once told me "yeah it's a great theory".

[Mary B]

She told me to sit straight to the bike we are going down and she laid it over smooth. Drove the bike home, saddlebags, foot pegs got chewed is the worst damage. Her husband said it looked like a textbook maneuver. He was about 100 feet behind us so ad time to stop. Really narrow 2 lane blacktop that crosses the river near me.

She now has a tricked out Harley trike I have ridden a few times. Sweet ride!easier handling than a bike, especially since her husband builds hot rods and can't leave the bikes stock. Had the big 140hp motors... she has the same motor in the trike now and it moves. She tows a small ultralight camper with it to one of my fishing spots I took them to.

[Bruce S]

Having laid a few down myself. I can say it works.
I am a firm believer in leathers and boots! Right along with a full face helmet.
The wife found out when an old lady blew through a stop sign she didn't see I bought her a Harley full-face helmet when she got her first Twist-n-go and passed her license test.
 
I still have the ARMY boots that saved my ankles from laying down the Kow 650C in Großauheim in '77.

Cheers!

Bruce S