Yaw bearing tower stub question.

[fabricator]

Hello all, I am building a seventeen foot machine, I lasered out my rotors and got

my wheel hub, I had to turn the back of the hub to get it running true, but now it

runs nice and straight.

I'm kinda thinking ahead here and contemplating using a tapered roller bearing on

the top and bottom of the tower stub with the races in the yaw tube, it will be a

little more expense and more work but it seems like it would be worth it, any

opinions would be greatly appreciated.

[cdog]

I used 2 flange bearings, look at my pics,

Cdog.

[Watt]

Is this the picture?  http://www.otherpower.com/images/scimages/4506/DSC01807.JPG

[TomW]

I will just mention that folks have reported issues with furling on machines using bearings rather than tube over tube for a yaw "bearing".

Something to do with how the bearings are too easy to move and affecting how it yaws and furls.

Just tossing that out. I read it here more than once.

Might warrant a bit of research before you commit in hardware.

Maybe someone with direct experience of it will respond.

Tom

[ghurd]

From much smaller, non-furling, not high in clean wind, windmills,

If it seeks / hunts the wind too easy the power seems to go down.

The blades slow down as it turns and wiggles about.

I would not want mine to yaw too easy, but 17'is a monster and I would want something to tame the wear on the pipes.  

Maybe tapered roller bearings full of heavy grease?  Just conjecture.

G-

[BruceDownunder]

From experience, I'm sort with Tom on the bearings system. I think you can get too much movement in a yaw system ,sort of defeats the purpose of keeping the face of the mill into the wind .. I use a tube over tube system with grease --seems to get sticky over aperiod of time and slow the yaw'ing down a bit . The wind direction MAY appear to be shifting ,but ,really, it's sort of fairly constant most times and a slower Yawing may have it's advantages...

Open for discussion!!!

Bruce

[SparWeb]

A seventeen-foot diameter mill will have larger tubes in the tower stub and the yaw mount than what I've shown for my 8-footer, but this should give you the idea.

[BruceDownunder]

Nice description ,Steven.

I really envy you guys taht can use that drawing thingo--could you post a site to something simple that even I could learn ??.

I replied to a post recently about bearings in Yaw movements. I'm sort of ,of the opinion that pipe over pipe with a bottom collar is ok ,,..My experience is that I don't want the mill to be wandering about too often ,,as my feeling is the wind will return in a few seconds anyhow ..

But,hey nice drawing,thanks

Bruce.

[Flux]

As someone brought up in an engineering background I tend to over engineer things but there are times when simplicity can be better.

The pipe on pipe scheme works well enough at least for smaller machines and the frictional damping does indeed seem to be a real advantage.

I have never been happy with taking the weight of the machine on bits of steel trying to cut into the top of a pipe so I have no experience of that and I don't intend to try it but although I use a thrust or taper bearing to support the weight I am reasonably happy to use pipe on pipe for the rest. In fact I do much as Sparweb has shown with a plastic sleeve rather than steel on steel but I just use a short bit at the bottom.

I have only built one machine with bearings alone with no sleeve bits and that one has slip rings so that I could use a control rope down the centre for a special furling scheme and shut down and I didn't want wires in the way. I wouldn't attempt slip rings without an engineered bearing scheme. That one does waggle in turbulent winds more than the ones with a more damped sleeve bearing set up but it is not an issue.

All commercial machines use bearings ( most have to for slip rings) and it would be a doubtful thing to sell commercially with crude yaw schemes but for home build you are probably best off doing what you are comfortable with.

My feeling is that a bearing to support the weight but with pipe on pipe for some damping is likely a good compromise.

Flux

[fabricator]

Thanks for the great replies, that drawing was exactly what I had sketched up, Flux, that seems like a reasonable compromise.

[fabricator]

Thanks for the great drawing, that is pretty much exactly what I had in mind.

[TheCasualTraveler]

Has anyone tried something like this,

     Shove a wad of greased cloth into the upper/ outer pipe so it sits at the top. Then roll in a single steel ball, small enough to fit inside the larger pipe but to small to drop thru the lower pipe. You would have a big single ball bearing that the machine could pivot on. I have been eying up those shiny balls in my pinball machine and thinking.

[TheCasualTraveler]

tch, should say "too large to fall thru the lower pipe."

[bobshau]

Nice drawing.

I use a greased brass plate instead of the tapered roller bearing to take the weight of my 20' machine. The rest of the bearing is pipe in pipe. This arrangement seems to provide adequate rotation in low winds but enough damping to provide minimal hunting during turbulent winds. Inspection after 1 year of service shows little, if any, wear on the brass.

Another factor is the size and length of the tail. It should be sized to provide a moment sufficient to hold the blades square to the wind with a 10 to 15 degree angle of attack on the tail fin. If this is accomplished, then the frictional counter moment from the bearing will be minimal.

Blessings and peace.

Bob

[cdog]

Yes, that is one of my pics, I had to have something with no slop so the brushes would track properly on the slip rings.

I can't say if it moves too freely or not, it is my first and only machine so I have nothing to compare it too.

I also have it placed in a good wind area, perhaps I would notice it's shortcomings in a marginal area?

Cdog.

[TomW]

Andy;

Interesting idea and it might work from a mechanical standpoint.

However, that might make dropping the cable down through the stub a bit of a problem?

Just a first thought.

I am not a builder so a sack [many grains] of salt may be in order.

My Zubbly [RIP] 2 meter [6.5 foot] turbine that I am testing to destruction by his request does not furl and uses the pipe over pipe yaw setup with a white plastic sleeve that acts as a wear surface between the tubes on the side and the top. I forget the name for the stuff he used but after a couple years it shows no signs of slop..

My 8 footer which Dan Built and is for a 10 foot prop uses the metal on metal yaw tube with furling and lots of blue marine grease. I wish I had put a brass wear washer on top of the mast to mitigate that sawing action from yawing. Maybe this year. I hads it down earlier this spring to fix a balance issue on the prop and it was obvious there was some wear on the mast tube at the top.I put a big muffler type clamp on the stub just below the outer yaw tube so I can see if it "settles" on the tube and to act as a stop in case it cuts through.

Tom

[scoraigwind]

These tapered roller bearigns need to be carefully aligned to work properly.  You need to set it all up on a lathe and turn it.  Or use 'self-aligning' bearing blocks.  I would question whether it is worth it.  

At Scoraig we mostly use big truck back axle bearings for yaw on this size of turbine. they have tapered rollers built in and they have a big hole down the middle for the half shaft so the wire can drop down there.    

I like a bit more stiffness in my bearings on the whole though.  The wires twist up a lot with these free-turning bearings.

have fun

[fabricator]

Well, this really helped, I believe I will go with the tapered roller bearing on top and something like a delrin plastic bushing on the bottom, thanks all!

[Ungrounded Lightning Rod]

That sounds pretty close to ideal to me.

Another possibility for the top is a clutch throwout bearing.  It's already a thrust bearing and has a big hole through the middle.  B-)

[Rover]

Tom it might be delron, we use a similar technique for sail boat rudder posts on older boats. Cheapest delron.. typically your local white bleach bottle is made of it

[fabricator]

One inch Sch 40 pipe is close to 1 5/16 od, I just happen to have two tapered roller bearings and races in my intentory, so as in the beautiful drawing above my stub

will be one inch pipe, and I just ordered a piece of delrin from McMaster for the

bottom bushing, things are lookin up! I can't see anything that could possibly go

wrong...............................

[luv2weld]

Maybe I'm reading this wrong. Are you saying your tower

stub is going to be 1 inch pipe? On a 17 foot machine??

That's a recipe for disaster!!!!

The line above Sparweb's picture is----

A seventeen-foot diameter mill will have larger tubes in the tower stub and the yaw mount than what I've shown for my 8-footer, but this should give you the idea.

Look closely at his diagram. The one inch pipe is a cable feed through.

It does not support the weight or stress of even an 8 foot mill.

His tower stub is 2.5 inch pipe-----And that's for 8 foot sweep.

Please tell me this is all a misunderstanding and I got it all wrong.

Ralph

[TomW]

Ralph;

Good catch! I read it and wondered but I am not a builder in metal so I thought I misunderstood it so did not comment.

I have no clue on a solid bar compared to tube for strength, either

Tom

[Ungrounded Lightning Rod]

Most of the strength is in the outer portion, so a thick-walled tube is a major fraction of the strength of a bar (until the walls get thin enough that it can crumple and lose its shape).  The amount of bending (and thus the amount of resistance to it in a given area by the spring force of the stretched/compressed metal) is proportional to the radius from the center of bending.

Just as the outer part of a turbine blade has most of the swept area, the outer part of the rod or tube has most of the strength - except in this case it's a cube law rather than a square law:  Radius times circumference for the area times distance from center at right angles to the bend direction (radius times sine of angle from bend axis) for the force resisting bending.

This is what I-beams are about.  The top and bottom of the I are the major strength members - half of a box-beam.  The center part keeps them together and also provides some strength against bending.  (You can cut significant holes in the MIDDLE of the bar of the I - where there's no stress when it's loaded in bending - and not weaken the beam noticeably.  This lets you run conduits through it.)

The I-beam is strongest when you try to bend it so one bar stretches and the other compresses, while the riser is bent the wide way (i.e. standing on the middle of it when it's supported by the ends in I position), considerably weaker but still somewhat strong when you bend it so the end of one side of each bar stretches and the opposite end compresses while the riser is bent the thin (folding) rather than the fat (stretching) way (standing on it in H position).

[SparWeb]

Hi Fabricator,

Please assure me that what you refer to as the "stub" is just the pipe that holds the wire....  right???  A couple of guys here are having trouble sleeping after reading your last message!

Common terminology would refer to the solid structural top of the tower as the "tower stub", so there could be some confusion going on.

Let's finish by saying I really hope you're using something like 4-inch Schedule 40 pipe, or MORE, as your TOWER STUB.

The forum is a mix of experienced builders and newbies so I'm not sure where you're coming from.

[fabricator]

Yeah, my tower stub is three inch 3/8 wall tube, the one inch pipe will be on top of the stub over which will slide the 1 5/16 ID roller bearing, it will look very much like that beautiful drawing several posts back.

[luv2weld]

So, if I'm reading this right------

The one inch pipe is going to be welded to the top of the stub

and then you slip the bearing over it. Then you put

the yaw tube over that.

If that is all true, then you are still using the one inch pipe

to support the stress of the entire machine.

Maybe you could make a sketch of what you mean.

I know you can do as you please. It's none of my business.

I just don't want you make a mistake that could cost you

a lot of money or someone's life!!!

A 17 foot machine is a lot of stress!!!

[fabricator]

OK, look at that multi colored drawing above, it will be exactly like that only

larger on every part.

[fabricator]

The only thing I may change is I may put a cap in the top of the stub with a grease seal so excess grease would be forced between the stub and the yaw bearing and not

down the inside of the tower and all over the wires, it would be a small amount but the way my luck runs it'll be the first thing I grab every time.

[SparWeb]

I think I can answer this, I found his previous posting a bit ambiguous, too.

The 1" pipe just hangs in the middle.  It's welded though the center of the cap to cetner the bearing, and hold the cable tight, but that's it.  The one in mine is a bit longer than the yaw mount, but I put in a little extra features.  Maybe if I made the drawing bigger - showed the bottom - it would clear up the concern.

[fabricator]

That is exactly what it is, just a center for the inner bearing race and a cable holder.