Author Topic: Day one. New project: Helical VAWT  (Read 11999 times)

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petemilligan

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Day one. New project: Helical VAWT
« on: July 15, 2015, 02:41:14 AM »
Photo shows 1/2 of the blade Jig. Happy to send CAD DXF files.

Objective - 2M high, 1.8M diameter Helical turbine. CNC cut EPP, NACA0018, 24cm Parallel chord, No washout. Biaxial 45 degree bias 600GSM Carbon, Vacuum Bagged.
Axial flux (Hugh's 2400 design). Will require 3:1 gearbox (more to come on that).

Going to be quite a project. Hoping to keep you updated as the project progresses. Would be ideal to get feedback/suggestions as this moves forward.

Pete
« Last Edit: July 15, 2015, 02:49:15 AM by petemilligan »

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #1 on: July 15, 2015, 02:50:46 AM »
You're seeing half of the Jig BTW.

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #2 on: July 15, 2015, 03:15:43 AM »
This might help to visualise things a little better.

lifer

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Re: Day one. New project: Helical VAWT
« Reply #3 on: July 15, 2015, 03:23:21 AM »
That's a very interesting project!

Do you have an estimate of the generated power? I've built a Lenz2 VAWT with similar dimensions (1.6m dia x 2.0m high) but I want to go further (larger) to accomodate my 3kW axial flux generator. The helical design looks great but I'm not sure about its efficiency. Btw, I'm using a 3:1 chain transmission, too.

Do you have a (simulated) pic of how it should look like in the end?

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #4 on: July 15, 2015, 03:41:30 AM »
Something like this. Sorry - All I really have at this stage.
I'll be mounting the generator at the base of the tower (Lattice structure tower). With two sets of bearings, there will be a drive shaft from the top to the bottom. Thinking Ali (Though also thinking about cost...).
I'd be happy with 800W to be fair.

Pete

lifer

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Re: Day one. New project: Helical VAWT
« Reply #5 on: July 15, 2015, 04:09:41 AM »
With two sets of bearings, there will be a drive shaft from the top to the bottom.

That's a good practice. I only have bearings at the bottom and there is so much stress on them, even if the bearings were oversized.   

I look further for your next steps. Good luck!

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #6 on: July 15, 2015, 04:31:06 AM »
Sort of - Perhaps I could have been clearer. The bearings will be top and bottom of the tower. See picture. Planning on using a couple of Meredith trailer hubs I've got in the shed.
I'd be interested in understanding more about the chain gearbox that you designed.

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #7 on: July 15, 2015, 04:44:09 AM »
And a poorly cast Axial Flux 2400 design for the bottom of the tower. The red-painted steel frame designed to fit on the triangular base of the tower (approx 2-3 feet from the ground).
(I'll stop if I'm boring folk)

Pete

lifer

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Re: Day one. New project: Helical VAWT
« Reply #8 on: July 15, 2015, 07:13:24 AM »
Oh, now I know what you meant by "bearings on both ends". I thought you have designed a bearing on the top end of the wings assembly, too.

Did you take into consideration the weight of that 8m shaft? Are you going to use two separate sections for the drive shaft (one for wing assembly and other for the top-bottom transmission shaft)? Anyway, for the wing assembly shaft you'll going to need a more sturdy and stiff steel bar, as there are strong forces at the bearings level. For the lower shaft, you might use a small diameter steel bar but there is a risk of bending/breaking at heavy rotation.

Don't you think it's a better idea to put your axial flux generator (and the gearbox) just bellow your helical turbine?

hiker

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Re: Day one. New project: Helical VAWT
« Reply #9 on: July 15, 2015, 12:25:19 PM »
Cool ...nice to see a new build..
WILD in ALASKA

tanner0441

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Re: Day one. New project: Helical VAWT
« Reply #10 on: July 15, 2015, 02:16:43 PM »
Hi

Impressive looking design. if you have only one set of spokes on the blades i would worry about whipping under gusty conditions. I would like to see two sets of spokes placed slightly asymmetrically placed in the blade. Allowing the blades to hang below the top of the tower and the bottom spoke just above the top bearing, plus two sets of bearings at the top of the tower and spaced apart. You could use quite a large diameter shaft for the first part of the shaft then the rest of the shaft could either be smaller or hollow. I would also put an AV coupling in the shaft to compensate for any whipping in the lower shaft..

By the way your not boring me and I doubt anyone else will find it boring. As for your gear box look up Chris Olsen's posts. He has designed and built oil bath chain gear boxes.

Brian.

Ungrounded Lightning Rod

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Re: Day one. New project: Helical VAWT
« Reply #11 on: July 21, 2015, 12:57:15 AM »
You need a very stiff shaft if you want to run it from the top to the bottom with just two bearings.

Imagine bending the shaft and letting it snap back, while supported by the bearings.  It will vibrate like a plucked string.  The longer the shaft, the slower the vibration.  The stiffer the shaft, the faster the vibration.

Now imagine the shaft turning, faster and faster, until it is going one turn in the period of that bent-and-sprung-back vibration.  As you approach that rotational speed, the shaft will form a bend that gets bigger and bigger until the shaft fails.  Even if it's perfectly balanced, the least vibration starts the failure which grows in positive feedback, pulling energy from the spin and putting it into bending the metal.

This was a big problem for gas turbines - to the point that, for years, there was some question whether they would ever work, rather than just tear themselves apart.  The eventual solution was to damp the vibration and get through the resonance quickly.  (Once it's spinning FASTER than the vibration period it's not a problem - until it reaches the second harmonic and does a DOUBLE bend, etc.)

I think there are solutions that involve more than two bearings, but I'm not an expert on this.

teelo888

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Re: Day one. New project: Helical VAWT
« Reply #12 on: July 26, 2015, 10:34:02 PM »
Now imagine the shaft turning, faster and faster, until it is going one turn in the period of that bent-and-sprung-back vibration.  As you approach that rotational speed, the shaft will form a bend that gets bigger and bigger until the shaft fails.  Even if it's perfectly balanced, the least vibration starts the failure which grows in positive feedback, pulling energy from the spin and putting it into bending the metal.

I had no idea you could get into resonance problems on a vertical shaft supported at top and bottom with no forces acting on it perpendicular to the axis of rotation?

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #13 on: July 27, 2015, 05:40:56 AM »
"with no forces acting on it perpendicular to the axis of rotation"

There is with two bearings - I think that was the point of the later part of this thread. The top bearing will act as a pivot, causing a lateral force on the remaining shart. Picture might help.

I'm working up the final design to use two bearings at the top spaced roughly a couple of foot from each other. CV joint near the Flux Gen. Dumping the idea of using trailer hubs. Will be milling out something more specific to the tower in 7075-T6.


tanner0441

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Re: Day one. New project: Helical VAWT
« Reply #14 on: July 27, 2015, 12:33:28 PM »
Hi

That was my reason for mentioning two points of support to the blades and two spaced bearings near the top of the tower. To transmit the the power down the mast I would consider a reasonable diameter tube. this will reduce whip and torsional flexing in the shaft.

Again use some sort of AV couplings to the top and bottom of the shaft.

Brian.

Frank S

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Re: Day one. New project: Helical VAWT
« Reply #15 on: July 27, 2015, 05:06:41 PM »
When working with any spinning shaft there comes into play what is known as the critical speed which is effected by several forces one of which is torsional stress.
   If I read your post correctly you plan to support your turbine both above and below the blades then possibly connect the shaft below this to transfer your rotational energy to the bottom of the tower where you will have your generator or other use for the energy depending on the total length you may find that you might have to section your vertical shaft into many shorter shafts using flex couplings and carrier bearings along the length.

   There are two main methods used to calculate critical speed—the Rayleigh–Ritz method and Dunkerley's method. Both calculate an approximation of the first natural frequency of vibration, which is assumed to be nearly equal to the critical speed of rotation. The Rayleigh–Ritz method is discussed here. For a shaft that is divided into n segments, the first natural frequency for a given beam, in rad/s, can be approximated as:
 Reference  Trefethen L, Bau D. Numerical Linear Algebra. SIAM 1997 pg. 254

\omega_{1} \approx \sqrt{\frac {g \sum_ {i = 1}^n {w_ {i} y_ {i}}} {\sum_ {i = 1}^n {w_ {i} y_ {i}^2}}}
where g is the acceleration of gravity, and the w_i are the weights of each segment, and the y_i are the static deflections (under gravitational loading only) of the center of each segment. Generally speaking, if n is 2 or higher, this method tends to slightly overestimate the first natural frequency, with the estimate becoming better the higher n is. If n is only 1, this method tends to underestimate the first natural frequency, but the equation simplifies to:

\omega_{1} \approx \sqrt{\frac {g} {y_{max}}}
where y_{max} is the max static deflection of the shaft. These speeds are in rad/s, but can be converted to RPM by multiplying by \frac{60}{2\pi} .
I live so far outside of the box, when I die they will stretch my carcass over the coffin

electrondady1

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Re: Day one. New project: Helical VAWT
« Reply #16 on: August 17, 2015, 02:49:59 PM »
buddy's gorlov style mill will top out around 200 rpm .
are the forces involved really that critical?

MattM

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Re: Day one. New project: Helical VAWT
« Reply #17 on: August 17, 2015, 09:44:01 PM »
Just seems like a top mounted rotor and a hub with three wheels at the bottom to ride against the tower would be more ideal.  Sit it on the tower like an upside down bucket.  Wheels need spring loading to keep tight to the tower as it torque bends the bottom rotor off center, because you do not want too much oscillating.

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #18 on: September 20, 2015, 09:06:58 AM »
Now ready for bagging the blades. The beds are being fixed to the helical frame. The other photo is of the cut cores. Two per blade (2 metre each). Very worried about the use of expanded polypropylene. A materials that is designed to resist chemical bonding. Best I'll get is mechanical.
This week they'll be skinned with 2 layers of biaxial glass @ 400gsm. Using a gloopy base of epoxy on the cores initially. The Spars are carbon fibre 20mm x 5mm with 15mm Balsa sheer webs.

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #19 on: September 20, 2015, 12:59:58 PM »
buddy's gorlov style mill will top out around 200 rpm .
are the forces involved really that critical?

Electron - I'm with you. Feeling like a retrofit for further stability is required later.

Pete

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #20 on: September 22, 2015, 12:34:52 PM »
Constructing the central shaft. Work in progress. A question before I need to rework the design. Would 30mm Steel shaft be sufficient for this design? (2M blades x 1.8 Dia). Do you think I can get away with a hollow steel shaft?

Top mount will have two sets of bearings for the steel shaft portion --> Coupler --> Ali shaft --> Bearing/Gearbox --> Gen.

Pete

electrondady1

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Re: Day one. New project: Helical VAWT
« Reply #21 on: September 24, 2015, 06:36:15 AM »
30mm is a whole lot like 1&3/16" dia.
if you have two bearings one at the top one at the bottom should be no problem.
if two at the bottom and none at the top it's difficult to say .
 i'm running a 5' tall drag mill 20" dia  on a 5/8"  shaft  with no top pin but it's very low mass.
weight and balance everything.

 

Harold in CR

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Re: Day one. New project: Helical VAWT
« Reply #22 on: September 30, 2015, 03:16:35 PM »

 For a bit more info, I am running a 6' (feet) tall 3' (foot) Lenz style lift/drag mill freewheeling (no generation mounted to it) at 15' (feet) high and 9'(feet) above the ground, on top of a hill, and have seen the wings go in a blurred stage, and it has a 1" dia. galvanized water pipe for the shaft and 2 pillow block bearing 1 on top and 1 on the bottom. There is a slight imbalance from a slight bend in the pipe that I was not able to get completely worked to a straight line.

 I have been trying modded car alternators with permanent magnet rotor, and, with normal operation with regulator. So far, no respectable output. Soon, I will have an axial flux sawblade alternator to experiment with.

petemilligan

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Re: Day one. New project: Helical VAWT
« Reply #23 on: June 26, 2016, 11:27:05 PM »
All, I can hardly say 'day one'. This project has taken much longer than expected. Mainly due to the complications of bonding to a low-energy material such as expanded polypropylene. Tip following much research: Permabond TA4610 & lashings of Coating resin. Anyhow - Few pictures; Mounts Installed on tower,  one completed blade (2 to go).

For the drive shaft, I decided to go with 6061 x 30mm for the top portion with a hollow 25mm for remaining. Simultaneously constructing gearbox (Chain driven) 1:3.

Pete

MattM

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Re: Day one. New project: Helical VAWT
« Reply #24 on: June 27, 2016, 06:01:03 AM »
Looks very professional and clean.  I am looking forward to seeing your project all come together.  Did you figure out the twisting on the shaft?

Ungrounded Lightning Rod

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Re: Day one. New project: Helical VAWT
« Reply #25 on: September 26, 2016, 06:18:12 PM »
30mm is a whole lot like 1&3/16" dia.
if you have two bearings one at the top one at the bottom should be no problem.
if two at the bottom and none at the top it's difficult to say .
 i'm running a 5' tall drag mill 20" dia  on a 5/8"  shaft  with no top pin but it's very low mass.
weight and balance everything.

To avoid the resonance problem I'd use (at least) THREE bearings:
 - one at the top
 - one at the bottom
 - one between them but not EXACTLY between them - at a distance where the spacings between the "middle" bearing and the top, vs. the spacing between it and the bottom, are relatively prime, i.e. have no common factors (or at least no small ones).
 - each of them mounted on an energy-absorbing rubber mount (of the sort you find in automobile suspensions and the like), with a shade over each shock mount to keep the sun from rotting the rubber.

Then you have to get up to many times the RPM where the whole shaft would resonate before you get a frequency where both the top and bottom unsupported segments of the shaft have a resonance that puts a node near the supporting bearing.

This way, no matter what equivalent frequency of vibration your RPM amounts to, at least one of the shock-mounted bearings will damp the vibration.

The more (appropriately intermittently spaced) bearings, the faster it will spin before there is a shaft resonance problem.

Let us know how well it works (and what spacings you used).  B-)

george65

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Re: Day one. New project: Helical VAWT
« Reply #26 on: September 26, 2016, 09:13:56 PM »
Then you have to get up to many times the RPM where the whole shaft would resonate before you get a frequency where both the top and bottom unsupported segments of the shaft have a resonance that puts a node near the supporting bearing.

Thats pretty clever thinking!

I'm going to try this concept with an engine I have mounted on some thick timber beams that has a vibration problem I can't seem to stem. If I use any thicker timber I'm going to have to use whole tree trunks.
I was careful to centre everything, maybe this could be a part of my problem.
Not the first time I have come into problems with trying to make things aligned, centred or balanced.  I thought that was good engineering. I'm not thinking I'll do things in my own rough and ready disproportional way and be better off!

Thanks for the insight.