# Summing up torques

DaTario
Is there any law of physics which forbids a mechanism by which several windmills located at different positions could be used to extract energy from the air current and to convert it into torque around one only axis ?

Thanks

Best Regards,

DaTario

Homework Helper
I'm not sure what the question is but why couldn't you do it with gears and pulleys?

Gold Member
Around only one axis, or using only one axle?

Having successive wind turbines located on the same axis could work, but wouldn't be sensible since the turbines in the lee would be sheltered by the front one, and not be able to generate as much electricity.

What would be the benefit of having successive turbines on the same axle?

Gold Member
If I understand your question correctly, then there is no reason why they can't be 'ganged'. As Brewnog pointed out, one eclipsing the other would result in minimal output from the one 'downline'. If, on the other hand, both of them are contributing, then tying them to a common output shaft is just a matter of straight mechanics. (It is either way, but not worth doing if only one has useful output.)
From a viewpoint of practicality, the trade-off point would be where using individual generators electrically linked is more efficient than the windmills being mechanically linked and running a single generator.

DaTario
I acknowledge all the contribution. Let me try to state the question again.

windmill A receives wind in its location and produces a torque A around its axle (thanks). Windmill B the same, but in other place.

Is there any way to use both windmill to sum up the torques, apllying it to rotate a third axle ?

Is there any way to use both windmill to sum up the angular velocities, apllying it to rotate a third axle ?

Mentor
With gears and pulleys, you can re-direct the torques in any direction you want. Consider the orientation of a car engine with respect to the wheels of the car - it really doens't matter, plus the car can be front wheel drive and the axis of rotation can be changed dynamically.

You could use the parallel axis theorem to find your moment of inertia about the third axle, but the problem is that the two windmills do not rotate about the third axle so this might be tough. but you could find the torque created by each windmill, then add them up algebraically and use that result to find a torque about a third axle. Just make sure you calculate the moment of inerta if the new axle first and then let:
$$Torque = I \alpha$$

Regards,

DaTario
People,

I know we can redirect torque from one axle to other by means of gears and pulleys. But my question, I guess, address another issue on this subject.

Supose you are trying to conect the rotation of two identical windmills A and B, by means of gears, to a thrid axle. Now, if windmill A is rotating faster, then windmill B will act a resistive component and will not, as it seems reasonable for me to state, contribute in this addition of torques I am trying to promote.

Best Regards

DaTario

Mentor
Well, if you are worried about speeds, you can use a continuously variable transmission. But I wouldn't - it would work better if all the windmills were operating at the same rpm and just producing different torques (modern power producing windmills have variable pitch props, and I believe operate at constant rpm).

If two windmills are just pinwheeling and not connected to a load, one would indeed slow down the other, but that's not what windmills are for: since both would be connected to a load that is absorbing a high fraction of the energy, both would contribute energy to powering that load, even if one windmill were producing several times the torque of the other.

DaTario
russ_watters said:
Well, if you are worried about speeds, you can use a continuously variable transmission. But I wouldn't - it would work better if all the windmills were operating at the same rpm and just producing different torques (modern power producing windmills have variable pitch props, and I believe operate at constant rpm).

If two windmills are just pinwheeling and not connected to a load, one would indeed slow down the other, but that's not what windmills are for: since both would be connected to a load that is absorbing a high fraction of the energy, both would contribute energy to powering that load, even if one windmill were producing several times the torque of the other.

Correct me if I am wrong: your conclusion is that if these two windmills are connected to rotate an axle which represents a load, then their torques will be summed up ?

Mentor
That is correct.

DaTario said:
People,

I know we can redirect torque from one axle to other by means of gears and pulleys. But my question, I guess, address another issue on this subject.

Supose you are trying to conect the rotation of two identical windmills A and B, by means of gears, to a thrid axle. Now, if windmill A is rotating faster, then windmill B will act a resistive component and will not, as it seems reasonable for me to state, contribute in this addition of torques I am trying to promote.

Best Regards

DaTario

I am fairly sure I answered your question in my previous post, where I explicitly state that torques can be summed up algebraically.

Regards,

DaTario
You could use the parallel axis theorem to find your moment of inertia about the third axle, but the problem is that the two windmills do not rotate about the third axle so this might be tough. but you could find the torque created by each windmill, then add them up algebraically and use that result to find a torque about a third axle. Just make sure you calculate the moment of inerta if the new axle first and then let:
$$Torque = I \alpha$$

Regards,

But you agree that if, dynamically speaking, one of the windmills happens to rotate faster than the other, then the slower one will act as a resistive component ?

Gold Member
DaTario said:
But you agree that if, dynamically speaking, one of the windmills happens to rotate faster than the other, then the slower one will act as a resistive component ?
It shouldn't if the transmission is set up properly. Over-running clutches or whatnot should take care of it. Think of how the differential in a car works to prevent drag from the inside wheel.

Mentor
DaTario said:
But you agree that if, dynamically speaking, one of the windmills happens to rotate faster than the other, then the slower one will act as a resistive component ?
No, it won't.

I think what you are envisioning in your head is a scenario with two pinwheel-ing windmills spinning at different speeds. Connect the two, and the slower one will drag-down the faster one to a speed halfway in between (unless they are geared or have a differential, as danger said). But in that scenario, there is no load anyway. Once you introduce the load, the rpm of both will be reduced to a point where the slower windmill would have to be recieving a lot less energy to act as a sink instead of a source.

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DaTario
russ_watters said:
No, it won't.

I think what you are envisioning in your head is a scenario with two pinwheel-ing windmills spinning at different speeds. Connect the two, and the slower one will drag-down the faster one to a speed halfway in between (unless they are geared or have a differential, as danger said). But in that scenario, there is no load anyway. Once you introduce the load, the rpm of both will be reduced to a point where the slower windmill would have to be recieving a lot less energy to act as a sink instead of a source.

So, in conclusion, If I introduce the load then, although both will have their spinning velocities reduced, I will still have the torques summed up. Is it?

Best Regards,

DaTario