Power Transmission Ideas for a Coaxial Wind Turbine 3

Hisham: First question - is it intended to be a "direct drive" application (where the generator shaft and turbine blade rotate at same speed), or something else (usually generator turning MUCH faster than turbine blade). Second question - what is the intended generator rating (more power at lower speed means more torque, which in turn means larger physical size and more weight). Third question - if the drawing you showed is correct, then the generator can accept ONE input shaft (but not two, which is really your issue).

Possible solutions: 1) run both turbine shafts into a speed increaser gearbox assembly with only one output (given the positional requirements, it means running one of the turbine jackshafts back past the generator to the gearbox). 2) If you try to do what you drew, you WILL need some type of clutch arrangement as the turbine shafts will not necessarily be operating at exactly the same speed ... UNLESS both blades are affixed to only ONE shaft. If the single shaft with two blades is used, you have what is essentially a right-angle (speed increasing) gear located where your "mystery element" sits.

Other considerations - mounting the generator vertically inside the "tower" portion will make it virtually inaccessible for repair purposes. Do you really want to go there? Typical crane cost to lift out a conventional wind generator (horizontal mount) on a modern tower runs about 60-100k USD per lift. That would be one lift to take the damaged unit down, and one lift to put the replacement (or repaired) unit up - EACH TIME IT FAILS. In comparison, the cost of a new 3 MW generator itself only runs about 90-120k USD.

Converting energy to motion for more than half a century

I think you will notice a general lack of aircraft with propellers at both ends; it's been done, but not often. Similarly a low number of co-axial propellers of any arrangement**. They are similar problems - exchanging mechanical energy inside with kinetic energy in the air.

It's not reinventing the wheel - it's reinventing the drag sled.

**an exception of sorts is multi-stage compressors and turbines where the fluid is restricted from bypassing the blades. Bypassing is the actual limitation of wind turbines. Trying to extract too much energy makes a barrier to fluid flow deflecting the wind around the blades where the energy cannot be extracted.

@Gr8blu



thanks a lot for the detailed response

firstly I should have clarified d this is a miniature wind turbine project. you should quite easily be able to carry the full model in your hands lol.

(1) No it is not intended to be direct drive. I had just forgotten to include Gearboxes lol.

(2) the generator's ratings are unknown as of yet. I will be told these tomrrow

(3) yes the shafts will most definitely spin at different speeds.

(4) I do not understand how a single shaft attached to both layers of blades could work and I don't know any gear that can do what you describe. Maybe a bevel gear pair? but I heard they are terribly inefficient

My main question is,
what kind of power transmission element can solve the problem of being input with two shafts spinning in the same direction at different speeds and needing to transmit the sum of that rotary power down the turbine tower?

This I think is the crux of the problem right now,

The differential gearbox of a typical automobile axle operates very similarly to what I think you're trying to accomplish. You might want to take a look at the gear arrangement for that.

Rod Smith, P.E., The artist formerly known as HotRod10

Bevel gears are reasonably efficient - where was this "heard?" It's best to search for information rather than "hearing" about it.

said:

Efficiency of Bevel Gear

Because most bevel gears are intersecting shaft gears, their mesh is almost always rolling contact, therefore their general efficiency is high, typically 98-99%.

Click to expand...

For balancing purposes it might be better to lock them in phase, turning at the same rate. This will ensure the downwind blades have a controlled disturbance from the upwind blades.

I think the best solution would be a differential like the ones in cars. There you can transmit the power from two coaxial shafts, which rotate in the same direction but in different speeds, to one shaft which is perpendicular to the other shafts. The only difference would be the direction of the power flow which shouldn't be a problem at all.