Wind powered perpetual motion machine on a treadmill.

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 ablackett 24 Jun 2021

youtube.com/watch?v=jyQwgBAaBag&t=563

Veritasium driving in a wind powered car which can go down wind faster than the wind.  

It's a shame the video proves it is possible, we could have had a right good argument about this one.

2
 CantClimbTom 25 Jun 2021
In reply to ablackett:

A sailing boat can travel faster than the wind. Gets its energy from the difference between the sail and the keel/board, leaving slower energy drained air in its air-wake. There is sort of a "leverage" of forces due to the angle of movement relative to wind (or the hypotenuse of a triangle being longer than the other two sides which are wind versus force)

This car can travel faster than the wind. Gets its energy from the difference between the blades and the wheels, leaving slower energy drained air in its air-wake. There is a sort of "leverage" of forces due to a gearing of the moment of the blade in air versus moment of wheels on ground.

It's all a big magic trick. By that I mean something normal and simple is going on but it is presented in a specific, confusing and unexpected way which makes the whole thing appear impossible. Yachts are difficult to conceptualise at first, but this car thing really obfuscates what's happening.

Wonder how much it cost to build it, and was it fabricated by a boat builder?

Greatly enjoyed watching the video. Thanks ablackett!

OP ablackett 25 Jun 2021
In reply to CantClimbTom:

Cheers, I’m still trying to square up the analogy of the two boats sailing in spirals around a cylindrical planet as being equivalent to a propeller. Which part do the wheels driving the prop play in this analogy?

 mondite 25 Jun 2021
In reply to ablackett:

> It's a shame the video proves it is possible, we could have had a right good argument about this one.

Eh. Since when do facts get in the way of a good argument?

Clearly a cgi video if you watch 22 secs in there is a pixel flip and realignment.

1
In reply to ablackett:

I won't say I fully understand how it works but I know I have gone well over windspeed on a windsurfer. I believe modern americas cup sailing boats can acheive 2 - 3 times windspeed.

It's still a bit hard for me to get my head round but there is no magic in it. I think this is just another demonstartion of the same principle.

Very expensive compared to a windsurf set up. Very cheap compared to an americas cup boat set up.

 GrahamD 25 Jun 2021
In reply to mountain.martin:

The best thing I heard to try to imagine the faster than wind thing was to imagine a thinish wedge of wet soap or ice.  What happens when you push down on it slowly ?

 Michael Hood 25 Jun 2021
In reply to mountain.martin:

> I won't say I fully understand how it works but I know I have gone well over windspeed on a windsurfer. I believe modern americas cup sailing boats can acheive 2 - 3 times windspeed.

But was this going completely downwind, because they show how it's easy to beat the wind by going diagonally downwind and tacking.

 Brown 25 Jun 2021
In reply to mountain.martin:

Presumably the conceptual challenge comes because we conflate the speed of the wind with the energy of the wind.

With a big enough collector we can clearly extract enough energy to move a small something faster than the wind speed.

I assume that with normal sails the energy available is dependent on the relative speed of the wind to the sail. This method appears to get round this by using the turbine to maintain the wind object differential speed despite the object speed increasing.

Clever but unlikely to break the laws of thermodynamics.

 jkarran 25 Jun 2021
In reply to Michael Hood:

> But was this going completely downwind, because they show how it's easy to beat the wind by going diagonally downwind and tacking.

The turbine blades travel diagonally downwind. The 'sail' going diagonally downwind on a flat then  rolled-up cylindrical surface idea is the clearest way I've seen of illustrating this. It's still brain bending and requires believing you can tack downwind faster than you can drift despite the much longer course which is itself brain bending to me.

jk

 CantClimbTom 25 Jun 2021
In reply to ablackett:

I can't be ar5ed to do the maths here but I'm predicting the theoretical/perfect top speed of this system is 3/2 times windspeed. Which is pretty poor compared to a land yacht.

Intriguingly, when you look at a kind of similar thing, the maths of the theoretical max energy the perfect wind turbine can extract from air (which is 2/3rds energy from air) you notice that the slowed air left behind the turbine blocks the air in front of the wind turbine which is why you can't extract 100% energy. As you do the maths you start with a huge heap of pi and squares and r and all sorts, but as you simplify it all just magically cancells each other out and you get left with 2/3 as the answer. It's such an elegant but of maths. Anyway Without bothering to do this here my prediction is after all your effort you'd end up with 3/2 for the answer. Points if anyone here can be bothered or has nothing better to do at work today

Edit: no it's not, I'll stop being lazy, the perfect machine based on a wind turbine could travel at 1 2/3 (i.e. 5/3) the windspeed because it can extract 2/3 kinetic energy from wind for its own kinetic energy on top of moving with the wind if we have zero friction and theoretically perfect energy extraction by the turbine. So top speed 5/3 the windspeed is perfect 100% energy use. 

Back to work everyone!

Post edited at 12:47
1
 Toerag 25 Jun 2021
In reply to CantClimbTom:

> I can't be ar5ed to do the maths here but I'm predicting the theoretical/perfect top speed of this system is 3/2 times windspeed. Which is pretty poor compared to a land yacht.

It's not about top speed though, it's about going faster than the wind directly downwind, landyachts can only do it by going diagonally.

 CantClimbTom 25 Jun 2021
In reply to Toerag:

> It's not about top speed though, it's about going faster than the wind directly downwind, landyachts can only do it by going diagonally.

Sorry I meant with the wind in my reply. It is about top speed. If the perfect system had a theoretical top speed of <1 times windspeed it'd be worse than the theoretical perfect square-sail so beating wind speed shows it is actually doing something more than a square sail. As my edit above this system has theoretical top speed of 5/3 windspeed if "perfect" (running with the wind) due to dead air limit the same as a static turbine is 2/3 extraction.

Since this only stands any chance direct with the wind, it's much better to have a land yacht, which can do thinks like cornering tack jibe etc that this silly turbine could never do.

Post edited at 12:54
 deepsoup 25 Jun 2021
In reply to jkarran:

> The turbine blades travel diagonally downwind. The 'sail' going diagonally downwind on a flat then  rolled-up cylindrical surface idea is the clearest way I've seen of illustrating this. It's still brain bending and requires believing you can tack downwind faster than you can drift despite the much longer course which is itself brain bending to me.

I got tangled up in this in a previous thread (which I can't find now, perhaps it was in the pub).  I think it was Wintertree who patiently explained it to me about a dozen times.

For me this was the wrong way to think about it.  The thing is that whether you're tacking or sailing directly downwind the wind is what's driving the sail forwards.  But the wind does not push the turbine blade round (when the car sets off and is moving below the windspeed, the turbine would be spinning in the opposite direction if that were the case).

It's the wheels of the car turning that drive the turbine blades around, not the turning of the blades that drive the wheels.  Look at the streamer on the nose of the car - from the point of view of the car while it's travelling downwind faster than the wind speed, the turbine blades travel diagonally upwind not down!  They are taking air from in front of the car and accelerating it towards the back.

 Trangia 25 Jun 2021
In reply to ablackett:

How refreshing to see a treadmill back in the limelight! Just like old times

 GrahamD 25 Jun 2021
In reply to CantClimbTom:

In the video, they reckoned they'd got to 2.8x windspeed.

 Trangia 25 Jun 2021
In reply to GrahamD:

> In the video, they reckoned they'd got to 2.8x windspeed.

That might become quite lively in a hurricane!

 john arran 25 Jun 2021
In reply to deepsoup:

That all sounds reasonable, but how do they get it started? Do they need to bump-start it? And if they take the handbrake off when stationary, does it go backwards?

 mbh 25 Jun 2021
In reply to CantClimbTom:

> Intriguingly, when you look at a kind of similar thing, the maths of the theoretical max energy the perfect wind turbine can extract from air (which is 2/3rds energy from air)

Being pedantic, but I think it's a bit less than that: 16/27

 jelaby 25 Jun 2021
In reply to john arran:

It starts by getting blown along by the wind, which it would whether or not it had the turbine, then the turbine starts turning and that makes the vehicle faster.

 deepsoup 25 Jun 2021
In reply to john arran:

I wondered if they might need to give it a push to get it rolling, but according to the commentary on the video they don't.  When the blades aren't turning they're effectively just a not very efficient sail and the wind alone is enough.  Also I guess any time the car is moving downwind below the windspeed there's an element of the turbine (and the rest of the vehicle) acting as a sail to provide a bit of thrust as well.

> And if they take the handbrake off when stationary, does it go backwards?

No, because the blades are driven by the wheels.  When the wheels aren't turning the turbine blades aren't either.  So the initial 'push' from the wind alone is still downwind, and then as it moves and the blades begin to turn they're turning in the opposite direction to the way the wind is trying to turn them - because the turbine is a fan not a windmill.  It doesn't turn with the wind, it pushes back against it.

That's the key thing to understand, which is surprisingly difficult to get your head around (it took me ages): the turbine is not a windmill that drives the wheels - it's a fan driven by the wheels.

When we've all completely got our heads around the land version, I suggest we take the discussion back on to the water.  Lets have the big air turbine mounted on a boat, and driven by another turbine under the waterline built into the keel.

 jelaby 25 Jun 2021
In reply to CantClimbTom:

If the turbine could be rotated on the vertical axis, you could turn it so it was always facing at the optimum angle between straight into the wind and backwards, and you'd be able to get power all the time, no matter what direction you were traveling.

I think there inevitably be a whole load of engineering difficulties mainly to do with the fact that the turret would always be trying to turn itself. Maybe using an electrical linkage between the turbine and the wheels would be best. Like a power generating turbine in reverse.

... That'd be totally mad wouldn't it? A vehicle apparently powered solely by its own regenerative brakes!

 jkarran 25 Jun 2021
In reply to deepsoup:

> It's the wheels of the car turning that drive the turbine blades around, not the turning of the blades that drive the wheels.  Look at the streamer on the nose of the car - from the point of view of the car while it's travelling downwind faster than the wind speed, the turbine blades travel diagonally upwind not down!  They are taking air from in front of the car and accelerating it towards the back.

It's hard to see what they're doing with the pitch control but I agree the axial flow through the turbine does appear to be front to rear. The wheels act a bit like a boat's keel resulting in high speed 'crosswind' motion of the sails. It's all very confusing but I don't disagree, the turbine mast is pushing the thing forwards slightly more than the wheels hold it back.

jk

 Maggot 25 Jun 2021
In reply to deepsoup:

> That's the key thing to understand, which is surprisingly difficult to get your head around (it took me ages): the turbine is not a windmill that drives the wheels - it's a fan driven by the wheels.....

... which moves the vehicle, which turns the wheels, which .......

Has a familiar ring to it.

 jkarran 25 Jun 2021
In reply to john arran:

> That all sounds reasonable, but how do they get it started? Do they need to bump-start it? And if they take the handbrake off when stationary, does it go backwards?

It's a variable pitch turbine, assuming they have a decent range of -ve and +ve pitch available it could produce wheel torque in either direction. The maker's explanation is it's aero-drag that gets it going to begin with which suggests they maybe don't have full +- pitch control or maybe it's just the tidier explanation.

jk

Post edited at 16:33
 john arran 25 Jun 2021
In reply to deepsoup:

... then as it moves and the blades begin to turn they're turning in the opposite direction to the way the wind is trying to turn them - because the turbine is a fan not a windmill.  It doesn't turn with the wind, it pushes back against it.

Therein lies my question. Most fan bades are fairly similar when looked at from opposite directions, so would act to work in reverse unless there's some significant one-way blade profiling designed in.

Assuming not, then even though the fan would be turning in the wrong direction at low speeds, the wind hitting the fan would be acting to slow it down. Hence my question about when it's stationary too. To act as a simple sail, presumably the blades would be locked until it has sufficient speed, to prevent the fan rotation countering the motive work of the simple sail.

 deepsoup 25 Jun 2021
In reply to jkarran:

> It's hard to see what they're doing with the pitch control but I agree the axial flow through the turbine does appear to be front to rear.

I don't think they have a pitch control, there doesn't seem to be anything in the video in the OP to suggest that they have.  The small scale model certainly doesn't have a variable pitch.

 deepsoup 25 Jun 2021
In reply to john arran:

> Assuming not, then even though the fan would be turning in the wrong direction at low speeds, the wind hitting the fan would be acting to slow it down.

Yes, but try looking at it the other way up - the fan hitting the wind is acting to slow it down.

> Hence my question about when it's stationary too. To act as a simple sail, presumably the blades would be locked until it has sufficient speed, to prevent the fan rotation countering the motive work of the simple sail.

While the turbine isn't turning the blades act as a simple sail, but there's no need to keep them locked because as they begin to turn the rotation doesn't act to counter the motive work of the simple sail, it acts to reinforce it.  The fan turns so that it's trying to push air from the front of the vehicle to the back, pushing back against the wind, and in doing so it also pushes the vehicle forward.

OP ablackett 25 Jun 2021
In reply to deepsoup:

They said something about varying the pitch to slow down, pull it forward - “if that doesn’t slow you down pull it backwards” I think they said.

 john arran 25 Jun 2021
In reply to deepsoup:

> While the turbine isn't turning the blades act as a simple sail, but there's no need to keep them locked because as they begin to turn the rotation doesn't act to counter the motive work of the simple sail, it acts to reinforce it.  The fan turns so that it's trying to push air from the front of the vehicle to the back, pushing back against the wind, and in doing so it also pushes the vehicle forward.

But surely, when at rest, the wind on the fan blades serves to act in the opposite direction, i.e. to turn the blades (backwards) and therefore to propel the vehicle in reverse. Clearly this must be balanced against the simple sail effect propelling it forward, but it still seems clear that the effect of the fan itself turning is counterproductive until the car is moving significantly quickly.

 Maggot 25 Jun 2021
In reply to john arran:

It's Bullshitl! I'm sure we could all write reams about it , staged by 'Professors' with a toy maker driver 😀

 jkarran 26 Jun 2021
In reply to deepsoup:

> I don't think they have a pitch control, there doesn't seem to be anything in the video in the OP to suggest that they have.  The small scale model certainly doesn't have a variable pitch.

The full scale does, in the vid I watched (may or may not be the obe linked) there was discussion of it and disagreement between the two usual pilots as to which pitch setting slows it at speed! As you say, it works with fixed pitch.

Jk

 deepsoup 26 Jun 2021
In reply to john arran:

> But surely, when at rest, the wind on the fan blades serves to act in the opposite direction, i.e. to turn the blades (backwards) and therefore to propel the vehicle in reverse.

I see what you mean, and it has made my head hurt slightly thinking about whether it can sail directly upwind this way.  I think it could..

> Clearly this must be balanced against the simple sail effect propelling it forward

Yes - I think the pitch of the blades comes in to play here.  From a standstill the wind blowing over the blades is doing two things - it's pushing the entire turbine forwards, and it's trying to turn the turbine in such a way that it'll drive the wheels backwards.  So it'll accelerate forwards if the drag on the whole thing exceeds the torque on the turbine blades translated through whatever gearbox it has to the wheels, and backwards if it doesn't.

> but it still seems clear that the effect of the fan itself turning is counterproductive until the car is moving significantly quickly.

The fan isn't counterproductive, as long as the car is moving forwards it's pushing air from the front to the back, so it's pushing the car forwards.  The torque required to turn the fan is coming via a gearbox from the wheels of the car, so that is counterproductive.  The fan is trying to push the car to go faster, the wheels are resisting and trying to slow it down. 

When it's going at a steady speed both forces are about the same but no laws of thermodynamics are being violated because its speed across the ground is faster than its speed through the air - more power coming in through the wheels than is going out via the fan, the difference being the energy that is going in to making the bearings hot etc.

 deepsoup 26 Jun 2021
In reply to jkarran:

> The full scale does, in the vid I watched (may or may not be the obe linked) there was discussion of it and disagreement between the two usual pilots as to which pitch setting slows it at speed!

Ah, I didn't catch that (or the dialogue that ablackett mentioned above).

There is a bit in the linked vid where Neil, the owner, is up a ladder tinkering with it though and I could be mistaken* but it looks very much to me like it's adjustable but not variable if you see what I mean.  The hub looks like it just clamps the blades on to the end of a simple drive shaft so they can be adjusted by hand and there doesn't seem to be any mechanism there for the driver to change the pitch while it's actually moving.  Like going to red alert in Starbug - you can do it, but you need Kryton to change the bulb.

I'd post a screenshot, but I don't have photo posting privileges any more. 
It's one minute in to the vid in the OP: youtube.com/watch?v=jyQwgBAaBag&t=60

Edit to add:
*No, hang on.  I think I am mistaken.  Maybe you're right and that hub is cleverer than I thought.

Post edited at 10:57
 deepsoup 26 Jun 2021
In reply to jkarran, john arran and ablackett:

D'Oh.  Should have looked at wikipedia sooner.
https://en.wikipedia.org/wiki/Blackbird_(land_yacht)

Following some of the links, here's a bit on the Discovery Channel about it:
youtube.com/watch?v=DPvGTjmn9y0&

Blackbird can (and has) sailed directly upwind, and has been clocked sailing upwind at 2x wind speed.  It doesn't explicitly say so on there, but I'm convinced now that you're right and I was wrong - it must have variable pitch blades on the prop.

This was also done by a Californian by the name of Andrew Bauer back in 1969 (he *definitely* had a variable pitch prop).  There's a little bit of silent 8mm film of his machine here: youtube.com/watch?v=yFPomTq_PRU&

Andrew Bauer wrote a paper about this (and about his machine specifically), which is archived here:
https://projects.m-qp-m.us/donkeypuss/wp-content/uploads/2009/06/Bauer-Fast...

He goes into some detail about how his machine could travel upwind in 'windmill mode' (prop turning with the wind and driving the wheels), downwind faster than wind speed in 'propeller mode' (prop turning against the wind driven by the wheels), and downwind up to about 0.55x wind speed in either mode.  (And also delves into the theory of doing it on water.)

 deepsoup 26 Jun 2021
In reply to Maggot:

> ... which moves the vehicle, which turns the wheels, which .......
> Has a familiar ring to it.

Sorry, missed this earlier.

Yes, it looks like a perpetual motion machine.  But it isn't one. 

It derives its energy by slowing down the relative speed of the wind over the ground (thereby reducing the kinetic energy of the wind) - or in the case of the model that advances up against the 'flow' of the treadmill belt in still air, by applying a braking force to the 'ground' of the belt and making the motor in the treadmill work a little bit harder.  In still air relative to the ground it won't go anywhere - it's highly counterintuitive, but there is no 'woo' whatsoever.

 Baron Weasel 30 Jun 2021
In reply to GrahamD:

> The best thing I heard to try to imagine the faster than wind thing was to imagine a thinish wedge of wet soap or ice.  What happens when you push down on it slowly ?

Steve Mould has a video explaining it in layman's terms. 


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