Author Topic: Flyball (Read 5860 times)

Seedler · « **on:** September 17, 2006, 02:43:07 PM »

Hi,

It seems that every time I come on here asking for help it is about pitch control systems. Well, I'm still at it. Its starting to do my head in trying to get a system to run smoothley. But I wont give up.

My problems are:

When the system actually does work it suddenly feathers the blades back and forward and gets into a strange rythm that violently shakes the tower.
This is the design I used. I got it from this forum.

The problem is that when the blades get up to speed the centrafugal forces on them actually bend the blades so that the tips line up with the centre.

Any help on making this work would be appreciated, or do I need a new design?

I have been looking at some flyball designs, but cant seem to work them out. They seem to be basically the same as mine except for the fact the blades are in the centre (not offset). But how does this work? centrafugal force makes the weights want to move out from the centre, but if they are in line with the blades how do they turn them?

Does anyone have a design for a flyball system that would just tell me exactly what to do?

Dee.

wdyasq · « **Reply #1 on:** September 17, 2006, 10:07:43 AM »

It will be hard, if not impossible, to diagnose your problem without seeing it and checking several things. The fluxuations can be caused by a number of inter-actions. If the backplate flexes it could mechanisms could bind things. There may be a 'hard spot', slightly bent shafts caused by blade pressure or improper welding. A sticking 'Collar'or binding ring or spring could cause it. The weight of the blades and fly-balls may be 'breaking over' center. It could be a combination of these things.

So - a short answer, no I can't help you. But, there are a few things that may help you sort the problem. Good luck and let us know...

Ron

maker of toys · « **Reply #2 on:** September 17, 2006, 11:23:18 AM »

I think you're about to teach yourself a LOT of engineering the hard way. . .

improper aerodynamic balance, possibly caused by mounting position on the profile, or centrifugal or lift forces, is a avenue to explore. based on your comment about the blade tips changing where they track, this is a strong possibility. solutions to this will probably involve new or substantially modified blades with different bending and mounting characteristics.

too much flymass or too little spring might also cause your problems.

run the thing on the ground without blades and watch what it does. you might go as far as to put weight equivalent to the blades on the thing, such that the 'blade' mass runs at the blade CG station. . . in fact, that's what I would do in your position.

if it's really, really, REALLY well behaved, look at the blades.

if it's still violent or marginal, look to the weights, the spring, and all the things Ron mentions.

too, if your flymass is a significant fraction of the total rotating mass, you'll have major hunting problems as the moment of inertia changes due to the flyweights changing station. . . .

the trick with troubleshooting something this complex is to make gradual changes in ONE VARIABLE ONLY until you satisfy yourself that that variable is not part of the problem.

good luck!

-Dan

Seedler · « **Reply #3 on:** September 17, 2006, 12:22:30 PM »

I ran the rig without blades on the ground before I erected it and it ran perfectly. but what I found out later was that when blades are attached and spinning away through the air they generally want to stay parallel to the wind (their normal position). This means it now takes more force to move them. So a bench test cant be done here.

This is how I found out about the power of centrafugal force. The first time I put it up the system was not strong enough to pitch the blades. the thing ended up going supersonic, scary moment, especially when you hear that helicopter sound. When I evenyually got it down all three blades were bent back in the opposite direction of rotation about 10 degree. This is how the blade tips ended up in line with the centre.

As before if anyone has a diagram design on how this works I would be very greatful.

Dee.

stephent · « **Reply #4 on:** September 17, 2006, 12:44:59 PM »

You may find a dual spring arrangement (inner/outer) like some valves have in an auto engine will help with the "harmonic" bouncing...

With just one spring there will be a point that there will be a "tuned" spot of rpm/angle that will show some to a lot of destructive whipping action.

Even with 2 springs there will be the same action somewhere. but usually the two different spring rates will take the resonance out of normal operating area....usually,, sometimes.

RP · « **Reply #5 on:** September 17, 2006, 01:09:09 PM »

Can you show us how the blades are mounted on the spars (blade shafts)?

Because they're offset, there may be significant centrifical forces acting on the blades regardless of the flyweight system.

Flux · « **Reply #6 on:** September 17, 2006, 01:41:16 PM »

It could be blade mounting but much of the trouble sounds like excess friction.

Your sliding sleeve may be too short in relation to the shaft diameter. Not sure what the bearings holding the blade shafts are, but if they are plain bushes then there will be a lot of friction with the thrust from the blades. The angle of the rollers on the slots in the centering mechanism get progressively worse as you feather the blades. You would have done better to split the angle either side of the 90 deg point.

If the centre of the blade axis is in front of the blade shaft centre it will probably be unstable.

As others have said, pictures or detailed drawings would help.

Flux

scottsAI · « **Reply #7 on:** September 17, 2006, 03:06:33 PM »

Hello Seedler,

I'm working on a 10kw 24' wind gen, 3ph induction motor/gen with active pitch control.

Thinking about going to 20kw at 30'.

Pitch control has not been designed yet.

Will have an electronic pitch controller. RPM controlled to 3%. (stall controlled.)

If interested in sharing ideas contact me. I think electronic pitch is lower cost more accurate.

Sorry general posts take way tooo long to explain the history and the question to get useful answers.

So far the outline is 14 pages long. (big text:-)

Have fun,

Scott.

inode buddha · « **Reply #8 on:** September 17, 2006, 03:27:18 PM »

Since your setup reacts so quickly, I am inclined to believe that your governor/pitch control was originally intended for an engine. They were quite common about a hundred years ago.

Nowdays the materials and manufacturing are much better, but I still think the flyball governor is a good idea. To decrease the sensitivity I would either increase the spring pressure (strength) or add a lot more weight to the flyballs.

I've got some really old reference manuals on these (from the 1920's) which I could scan and upload, but it may take a day or so to find them and do it. Meanwhile a handy hint is that the GMC TH-400 auto transmission uses a similar setup to regulate the shifting.

Seedler · « **Reply #9 on:** September 17, 2006, 04:26:29 PM »

Thanks for all your comments. I'll try to get some pictures uploaded tomorrow. They will be from a camera phone so sorry if the quality aint that good.

ScottsAI, I'd be intersted in your idea of an electronis system but I dont know alot about circuits.

Dee.

Walt · « **Reply #10 on:** September 17, 2006, 04:37:18 PM »

Seedler,

It seems to me that you may have already seen what the problem is. You said that the blades had moved back to be in line with the center shaft. Being that you have the weighted pivot at a 90 degree angle to the center, and if your blades are connected directly in line with the pivot shaft. That would put the blades 30 degrees out of alignment with the center shaft. The centrifugal force on the blade is trying to bring it back in alignment. Not knowing how you have your blades attached to the shaft there is little that can be said as for a remedy to the problem. It might be possible to alter the angle of the shaft to blade interface.

I think if you could alleviate this problem that you will be well on your way to a working governor. Finding the centerline of the blade and the exact angle of the shaft to blade will be the next obstacle.

Pictures would help.

.

SamoaPower · « **Reply #11 on:** September 17, 2006, 05:04:42 PM »

Where did the blades bend? Was it the pitch rotation shaft or the blades themselves? What is the rotor diameter and the blade material? What material and size are you using for the pitch shaft?

As Flux points out, the location of the pitch axis along the airfoil chord line is significant to stability. What airfoil are you using? Hopefully it's not arbitrary.

My VP hub, with four years running time, uses three hydraulic dampers (like shock absorbers) to help with pitch stability.

kamikaze · « **Reply #12 on:** September 17, 2006, 06:03:11 PM »

Hi Dee,

Firstly I'm pleased you are persisting with a pitch control system. Most people seem to think it is too difficult.

There is a phenomenon called CTM or Centrifugal Twisting (or Turning) Moment which I have never seen mentioned on this site before. Basically, the mass of any rotating object will attempt to move to the plane of rotation, eg a weight tied to a string and swung over your head. The faster you swing it the closer it gets to the plane of rotation.

In the diagram the mass of the blade forward and aft of the plane of rotation tends to rotate or twist the blade, effectively flattening the pitch. If your blades were free to rotate in pitch, ie no pitch control connected, the blades would move to about zero degrees pitch and the turbine would stop turning.

The force of CTM is surprisingly strong. A blade which is not torsionally rigid enough can twist at high rpm, and reduce its pitch. If the turbine was overspeeding this would make things worse.( or maybe better if the blades stalled.)Your initial testing with the flyweights meant they only had to overcome spring force. The greatest force is the blade CTM.

It is necessary to include a fine pitch stop in your pitch control design which sets the blade pitch at the normal operating angle (5-10 degrees or so). I noticed that your turbine would suddenly feather the blades back and forward. I think that the mechanical setup of flyweights, spring, and blade pitch linkages may need modifying. I suspect that after your flyweights overcome the threshold when they first start to move,then they can continue moving too easily until they are at their fully feathered position. The setup should allow the flyweights to move a little earlier, but meet increasing ( maybe exponential) resistance until the fully feathered position. This may occur over ,say a 100rpm band.

This diagram shows something more like a flyball governor. The linkages allow the initial flyweight movement to occur relatively easily, but requiring progressively more force (rpm) to fully feather.

Anyway, best of luck.

The Professor · « **Reply #13 on:** September 17, 2006, 06:36:49 PM »

My advice is to ad a car shock absorber to the pitch control. That might dampen out the osolations.

15 years ago I made a 16' mill with pitch control. The blades were 1 x 6's sandwiched between two steel plates welded on bicycle front fork assemblies with their bearings. Theese blades went through center, not off set like a dunlite blade hub. comparing mine to your drawing above, the weights were at 1 o'clock and would try to move to 3 o'clock, which is a slightly greater diameter. Let'see, standing up wind looking back at the mill, the blades turn clock wise. The weights pointed towards me but favoring towards the blade's trailing edge. As the speed increases the weights over come the spring presure and seek the greater diameter in the plane of rotation, increasing the blade pitch.

scottsAI · « **Reply #14 on:** September 17, 2006, 06:44:45 PM »

Electronics is the easy part. Really. Don't need any help there.

Dealing with the hardware is the challenge:

Make it cheap enough.

Make it strong enough.

Make it durable enough.

Make it simple enough.

Make it light enough.

Make it duplicable. Ok enough:-)

Getting someone that needs it and will build it. I can't.

These are the challenges.

Interested?

Have fun,

Scott.

ghurd · « **Reply #15 on:** September 17, 2006, 07:40:46 PM »

Off topic I'm sure, but 16'? How did the bike bearings hold up?

G-

The Professor · « **Reply #16 on:** September 18, 2006, 06:00:41 AM »

The front fork assemblies worked great on that mill, withstood the bending and centrificial forces. Long term there would have been a lube problem because of the non sealed bearings. It did have some friction in the 3 blade connecting linkages. It would rev up and then change pitch suddenly. The addition of a car shock absorber smoothed this out.

Seedler · « **Reply #17 on:** September 18, 2006, 06:53:49 AM »

Ok I got a pic. Like I said its very bad quality so I dont know if it helps at all. It might give you some idea. It is the exact same design as the one in the original post except mine turns clockwise.

The centre rod has the sliding collar and spring on it.

I think I'll try a few of your ideas. I'll go for the car shocks.

Kamikaze would your linkage type covner work the same if the weights arm was attached to the sliding collar?

Dee.

kamikaze · « **Reply #18 on:** September 18, 2006, 08:19:15 PM »

Hi Dee,

The flyball governor diagram I drew is a very basic schematic only. Preferably you would use 3 identical weight arms, etc. Of course if you just connect the weight arm to the sliding collar it wouldn't be able to move.The linking rod ensures that the flyweight force has to increase exponentially for further movement of the collar. You could add a similar link to your existing design to achieve the same effect, but you would still have the problem with offset blades.

Cheers

coldspot · « **Reply #19 on:** September 18, 2006, 11:59:54 PM »

Seedler-

I don't know if this will help but

Jacobs hub pictures

Exploded view, from probebly falling off tower,

(I don't know I got it this way)

Anyway, cool you are trying it!

Good luck!

Flux · « **Reply #20 on:** September 19, 2006, 02:32:32 AM »

Your scheme is the same as the Dunlite except that they mount the weights on the blade shaft.

One thing that may help you is to start with the fly weights at a larger radius so that you have less change of force with radius over the control range. If it is made as in your drawing you would need to bend the stalks holding the fly weights, perhaps to 45 deg.

The other thing that affects operation is the length and rate of the spring. A long spring well compressed will give the control a high gain. A stiffer spring with little initial compression will reduce the gain of the loop and help stability.

You don't want to change pitch too drastically for a small change in speed, so you want a low spring pre-load and a considerable stiffening with further compression.

The more friction you have in the mechanism the wider the speed change needs to be between start to furl and maximum pitch.

I have a feeling that you are going to full pitch change in a small increase in speed.

Normal friction will make things worse, fluid friction will help, so the hydraulic damper should help but should never be needed.

You could incorporate it into the sliding sleeve mechanism, anywhere else would be very tricky.

Flux

jacher · « **Reply #21 on:** November 07, 2006, 05:13:08 AM »

I have the same problems too. Thanks for the tips. I am a beginner and live in a very hot and humid place. How can I protect my gear from the elements? Without sacrificing performance of course. Also, any tips on what kind of blades to use?

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Author Topic: Flyball (Read 5860 times)