Elvo

Big if true

Introducing Arofly, ?the world?s smallest power meter? + video | road.cc


A pitot tube is a pressure measurement instrument that measures fluid flow velocity. As well as being used in aircraft (not just the F-117!), pitot tubes measure the water speed of boats, for example, and liquid, air and gas flow speeds in industrial applications.

The inventors say that once attached to the valve of the inner tube, the Arofly measures the tiny variances in air pressure to work out the power being applied by the rider. That's all we know right now. Sorry. We've asked for more info though.

The Arofly has an operating temperature of -30°C to 85°C – safely covering everything you’re likely to ride in – and it’s said to be both waterproof and dustproof.

Dopefish905

Skeptical it will be as accuarate as other PM's but for the adverage joe, might be a good bargain! This is the single reason I haven't dropped $$$ on a power meter yet, seems like every month they get cheaper and better ways to attach them to your bike..hubs -> cranks arms -> pedals -> almost shoes -> Valve stems? The technology is advancing to quick for me to shell out a grand or so, but I'm cheap as well 😆

DXchulo

Interesting. Kind of like the iBike in that it doesn't actually measure power, but uses other data to estimate power output.

With the iBike being so expensive it's always made sense to me to just spend a little more and get real power numbers. Something in the $129 range might actually make me think twice. Assuming it's a good product, obviously.

Dan333SP

That's wild, it claims to measure cadence as well. I wonder if your "cadence" is measured by pulses on the tire from your pedal strokes rather than a traditional revolution counter near the crank.

If it's reasonably accurate when compared to a traditional power meter, it could be a game changer for people who can't afford to pony up for traditional systems. I'd definitely consider it.

I'd really like to know more about how it estimates power.

dalava

There is no such a thing that measures your direct power output yet; all the power meters in the market use data from different measuring point to DERIVE your power output, e.g. crankarm based uses strain-gauge.

79pmooney

I need more info. A pitot tube measures the difference in air pressure between still air and moving air and detects speed from that. (On a valve stem, that speed is almost twice yours then it is at the top.) At the bottom, it is not moving. Now it can read static air pressure directly at the bottom so it could estimate you altitude change, ie climbing or descending. But it has no idea of your weight or aerodynamic characteristics. You could tell it that info but still it would hardly know if you were tucked in the drops or riding no-hands.

Tell me more. (Manufacturer/marketer)

Ben

CliffordK

Hmmm...
Likely one could use a combination of centrifugal force + micro accelerations/deceleration to estimate speed and change of speed under ideal conditions. Elevation + rate of elevation change? GPS? Actual magnetic sensor?

As mentioned in some of the comments, one would also need to estimate wind direction and speed including drafting.

So, this is probably more accurate than simple GPS based power on Strava, but not as accurate as pedal, crank, or hub power meters.

WalksOn2Wheels

I could be very, very wrong, but it would seem to me that if we're talking about differential air speed, we also need to factor in frontal drag. That's too individual from person to person and hugely individual from sitting up vs. tucked into an aero position. I mean, maybe they have an assumed coefficient that is average enough to give close enough numbers for 129 bucks, but we'll see.

Isn't there a handlebar mounted power meter that does sort of the same thing with airspeed? Perhaps they happened upon a more accurate algorithm by placing it on the valve stem. Sort of a reverse brake dyno based on airspeed. Interested to hear more.

CliffordK

I found the manufacturer's website.
arofly
https://www.arofly.com/

So, it can actually be purchased.

I saw the cadence too which surprised me a bit.. But, as you pedal, 3:00 & 9:00... you get a micro acceleration. 6:00 & 12:00, you essentially coast and get a micro deceleration. Even if you are pretty uniform with your crank stroke, those accelerations and decelerations will be there.

It doesn't matter where one is in the wheel rotation. If you can accurately detect those micro accelerations, you can calculate cadence.

CliffordK

How about this...
Whenever a person coasts, one should be able to calculate the drag.

So, if one assumes the power hits 100% at 3:00 & 9:00, and 0% at 6:00 and 12:00, then one is effectively coasting briefly on every pedal stroke. From which one should be able to get a good drag calculation.

Of course, the calculations are messed up if the power at the bottom of the stroke is significantly non-zero.

Psimet2001 

It is essentially an iBike. Read up on iBike. Then move on.

Dan333SP

From what I can gather, it's not measuring air speed around the wheel, it's actually measuring pressure inside the tube. I guess there's a pulsing of air in the valve stem as the wheel rotates, and presumably there are smaller pulses associated with pedal strokes.

But you'd also get a lot of false readings due to bumps, pebbles, out of saddle efforts, ect. I'm dubious that it could distinguish between all those tiny variations in pressure and give you an accurate reading on cadence, power, or speed.

69chevy

"Pedaling on a bike creates energy." (from manufacturers website)

Dan333SP

ORLY?



I'll give them the benefit of the doubt and assume it's just a poor translation.

cycledogg

iBike and this ---> PowerPod Powermeter | ProBikeKit.com

PepeM

Bought one of those (well, the Powerpod) for $200 a week or two ago.

wphamilton

Detecting changes in tube pressure could get cadence, easy. If it's measuring apparent wind speed also, getting the bike speed is easy (a wheel rotation is the cycle minima).

When we thrust on the pedals, that's bound to alter the pressure inside the tire. How much surely depends on the power applied, and that would be regardless of grade. Personally I'll have to think on it more, but it seems to me that (if I have it right what it's detecting) it has everything it needs to derive power.

I can't help but think that properties of the tire will affect pressure changes and throw it off. But if it's been tested with different tires and found to work accurately, or even calibrated for tires (if indeed necessary) I don't think I will have any problem accepting that it works.

wphamilton

I think you could use Fourier Transforms or similar to filter out the noise.

Seattle Forrest

A distinction without a difference. Direct force meters measure torque and rpms, from which power can be calculated with complete accuracy.

superdex

and this is the bike they picture??




That, plus the way the copy is written, has me very skeptical. How does it get heart rate?

And I think the cadence might be a little simplistic: "Cadence is proportional to Speed. The more Cadence, higher the speed."

super skeptic goggles on....

CliffordK

I'm not seeing anything that indicates tube pressure vs outside pressure (and using valve simply as a holder).

If one sits on a bike still, then the tube pressure will essentially equalize no matter where the valve position is. Riding is more dynamic, but it is hard to envision how it will work.

Here is a good description of flow meters.
Types of Fluid Flow Meters
The Pilot Tube (And Venturi) flow meters are all about pressure differential created by flow. A static pressure meter really wouldn't be described as a pilot tube.

So, I'm voting for a valve stem to hold it in place, but all measurements are from the outside.

PepeM

Not really.

Even the fanciest power meters like SRM and such publish a margin of error, so 'complete accuracy' isn't, well, completely accurate either.

CliffordK

Arofly says its 10-gram device can read power, speed, cadence and other factors | Bicycle Retailer and Industry News

So... for the HR, a 3rd party accessory. Simple enough.

As far as the cadence... it will be creating micro accelerations in the sensors which I presume they can detect. I assume a hub based power meter would be the same.

Dan333SP

This is what appears in the comments thread below that original article-

"Via the tyre valve the Arofly measures tiny tyre pressure variances. According to producer Taiwan’s TBS Group, “the bicycle tyre is the first to know your pedaling power effectiveness by its reaction force from the ground. Through core and patented algorithm and advanced calibration technology the precise pedaling power is registered and with that the cycling performance. The Arofly is a hi-tech, precision ‘Pressure Sensor’ that turns tiny air pressure variances into digital data.”

Arofly: World?s Smallest Power Meter - Bike Europe

Another post with more info:

Overall force on the ground (total front and rear) can't change due to pedaling, but there is a weight shift between front and rear. Push the pedal, weight comes off the front of the bike and onto the rear. Push the pedal harder, more weight comes off the front of the bike. The extreme case being where the front wheel lifts altogether and you do a wheely. So there is a direct relationship between the power you are hitting the pedal with, and the reduced pressure in the front tyre. Measure this on a cyclical basis, and its easy to filter out short term transients such as bumps, and long term changes such as temperature. I haven't done the maths, and currently have a few gaps such as whether it needs to know your overall bike plus rider weight. (I suspect that as it's only pressure difference you are looking at and weight is constant, that it cancels itself out in the maths, but that might be BS) Anyway, I think that's the gist of it.

superdex

a hub-based powermeter reads cadence via separate sensor, btw...