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TECH NEWS
Arofly - 3.jpgIntroducing Arofly, “the world’s smallest power meter” + video
A new power, cadence and speed meter called Arofly that attaches to an inner tube valve and weighs only 10g is available for US$129 (around £101).
Arofly sends your cycling data via a Bluetooth connection to be displayed in real time on a custom mobile app on your smartphone.
It has a diameter of 2cm, a height of 1.9cm, and fits to both Schrader and Presta (via a titanium adaptor) valves in seconds. The 10g weight includes the coin cell battery.
Obvious question: how the hell does it work?
“Originating from aerospace technology, Arofly is the result of years of research and cooperation between aerospace scientists and sports biomechanics professors, developing a patented air pressure differential technology based on the pitot tube design, from the F-117 combat aircraft,” says the Taiwanese group behind it, TBS Group Corporation.
Cycling sales blurb is chock-full of aerospace references.
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.
The Arofly is compatible with iPhone 4S or later and Android OS 4.3 or later.
How well does it work? We haven’t got a clue. We’ve not used the Arofly nor even got our hands on one yet. We’ll do our best to get one in for test.
For more information go to www.aroflybike.com.
Mat has been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a winner of the Cycling Media Award for Specialist Online Writer. Now over 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.
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73 comments
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Sorry my degree offends you - what would you rather I do? Pretend not to have one?
In my book, buggering about with minuscule variations in pressure reported by a slow sensor that no matter what the data sheet says will be prone to temperature drift is TOTALLY different to working with a fast strain gauge that will see a much bigger differential. I'm sure if you spend some time thinking about it, you'll get to this conclusion in the end. Or maybe playing with soldiers hasn't given you enough experience.
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No no offence whatsoever, I just didn't realise it was necessary to list qualifications on this board at the start of a post to try to justify themselves.
For somebody who claims to be an engineer, you seem to be very closed minded. Yes strain gauges are the traditional answer, but a decent set cost close to 3 figures and require a crank rebuild to fit. Doesn't it occur to you that if somebody really does have a £100 solution which takes 5 seconds to fit, it might be worthy of consideration, especially for those amateur cyclists among us who don't require a high level of accuracy?
You keep rabbiting on about temperature drift affecting the result, yet you don't know what algorithm the inventor has implemented. What are you a mind reader? For example if he has assumed zero force at the neutral point (pedal at 12 o'clock) and is only looking for differential pressure round a rotation, then temperature drift may not matter to him. Response time? No different to a digital strain gauge (or were you going to implement in analogue).
As for these "miniscule" variations in pressure you seem to think exist, let me give you an example of miniscule pressure changes. In my younger days I flew gliders and hang gliders. The primary instrument used in any form of gliding is a variometer, which measures changes in air pressure, and hence indicates by how much you are climbing or descending. In 1980, 40 years ago and long before the days of "systems on a chip" my £60 variometer could easily measure a climb rate of 1 foot per second, purely on air pressure change, and yes I really do mean 1 foot. Pick it up off a table, lift it one foot, it would indicate the difference based on air pressure change alone. In comparison the 10's of pounds force I am putting through my pedals which are trying to lift the front wheel off the ground are considerable!
Strain gauges undoubtedly give higher accuracy, not least because they measure the right side of the drive train, and also measure the power per leg. People on here have often posted wishing there were a cheaper alternative so why be so quick to dismiss such an alternative for which the theory is sound, when frankly, we don't have the evidence to know if the implementation is also sound. Nope, lets all put the blinkers on, and do everything the way we always have!
I had a quick look at the app store and the "arofly" app by Louis Chen has had zero reviews. He has got a Bluetooth remote control car app that has had 1 review.
I am yet to be convinced to be honest
But no one has seen it... and you can't buy it.
This has to be the most pointless post I've seen to date on Road.cc!!
If you want to increase awareness in this fictional product, just tweet about it!
You've literally copied info from the website!
What is the point?!
Ahahaha...
Will wait new KOMs in Zwift from dumb schoolboys using this empirical meter of "power" - like that who gives out 600w x15 min ... schollboy from pro pelothone)))
This is brilliant: a Fredcebo. Screw it to your inner tube valves and let the meaningless numbers it spews out convince you to ride faster. But, like a sugar pill is to expensive medication, it only works if you don't question it.
" the Taiwanese group behind it, TBS Group Corporation."
They are pulling your leg, T(otal) BS corporation....
Yeah as long as it's consistent you can do your own arithmetic on rides to work out what you should be riding at after you get used to it.
Hyper skeptical though.
Looks like it does measure tyre pressure variance. Here's what I managed to find (http://www.bike-eu.com/sales-trends/nieuws/2016/10/arofly-worlds-smallest-power-meter-10127915):
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.”
As that was from October 25th, I wonder why no-one's actually tested one of these?
If has an accelerometer in it, it could measure cadence easily. Unless you've got the smoothest pedalling stroke in the world, it could easily detect the slight pulse in acceleration going through the wheel on each power stroke.
Hmm... Going to have a lot of noise to remove from the road surface if it's looking for micro accelerations.
Like others I'd be very surprised if this is accurate but if DC Rainmaker reviews it I'll keep an open mind.
Completely useless to most without ANT+ though.
Where do people get this accelerometer Myth. The OP is clear, it measures air pressure, and as pressure in the tyre changes with each pedal stroke cadence measurement comes for free! Cadence is half the period of the pressure variation, power comes from the magnitude of the pressure variation. If you measure the front wheel, pressure reduces with greater pedal power. On the rear wheel it is the converse. Basic Newton's 3rd law. Simples!
The schematics are easily accessible online, it contains an accelerometer. As for its intended purpose, however...
I stand corrected. I can't see the schematics on their site. Do you have the link please?
I suspect most people talking about accelerometers just assumed it had one, rather than had read about them anywhere. The application for FCC approval in America shows schematics, etc.: https://fccid.io/2AJGD-AROFLY01 In the 'Block Diagram', the BMA250E component is a 3-axis accelerometer.
I suspect most people talking about accelerometers just assumed it had one, rather than had read about them anywhere. The application for FCC approval in America shows schematics, etc.: https://fccid.io/2AJGD-AROFLY01 In the 'Block Diagram', the BMA250E component is a 3-axis accelerometer.
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Thanks for that. I note they also claim the sensor measures cycling speed. A wheel mounted accelerometer would measure wheel rotations and therefore give speed. Tyre pressure sensor measures crank rotation, therefore cadence, and front/rear weight shift to give power measurement.
Whether it works or not, it is an interesting device, and certainly not cheap to develop. If only someone would put that amount of effort into developing a sensible bike camera with 6+ hours recording and without the aero of a brick!
The schematics show a barometer, but its range is 0.3 to 1.1 bar, so can't directly measure tyre pressure. And I'm puzzled by the reference to pitot tubes in the article.
Their website says they have Taiwanese and worldwide patents, but I can't find them. (Though I did find one for a power meter using a static strain gauge on the rear drop-out. Interesting idea)
I'm a bit sceptical too. I'd certainly want to know a lot more before I parted. But if something workable is available at this kind of price then i reckon there'd be a good take up.
The idea of measuring tyre pressure makes some sense. as asdfqwerty says, the pressure would vary in time with your pedalling, so it can work out cadence. it'd be pretty simple to filter out extraneous spikes caused by a bump as there's no way you could suddenly double cadence (as in get a 2nd spike in a wheel revolution). The pressure changes would also be a function of weight and force applied, so it could take that into account. Accelerometer(s) would work out wheel speed and rate of climb/descent.
It would never be as accurate as a meter that is actually measuring the forces through the drivetrain. But it could be a reasonable approximation. And as long as it is consistent with itself, does it really matter if it report 300 watts or 320 watts? Needs ANT+ though.
was reading a blog piece yesterday which says to rely on BLE only is going ot kill a product. Those of us with Garmins and that is a lot with want Ant+ and BLE are nowhere near killing it off (piece is on Ray Maker's things to read if interested) .
the standard is ANT+ and to develop something without to try and keep some costs down is folly, IMHO.
I'm in the BLE camp and I think that's the future. Yes, ANT+ is certainly more common these days, but most modern phones have a BLE stack built into them, so it's easier to get devices talking to your phone with BLE.
I think Garmin are somewhat resting on their laurels at the moment and all it takes is a good competitor using BLE to shake them up a bit.
It's the fact that you can connect ANT+ to multiple devices that makes it so versatile.
I can connect my power meter to my Garmin, Zwift and TrainerRoad all at the same time using ANT+.
If I was using Bluetooth (my pm is dual band) then I'd only be able to connect it to one.
I don't have any problem connecting my phone to multiple BLE devices either.
That is a different scenario. The point here is that ANT+ broadcasts, and doesn't require a handshake, so a cadence sensor for example can be picked up by a sportswatch, cycle computer and phone all at the same time. I use this facility as well. BLE can't do this.
I see - I didn't realise that.
However, I still think BLE use will increase in the future due to the sheer number of BLE enabled phones. There's also the argument that ANT+ broadcasts aren't secure, but I don't see that as being a problem (unless you're wearing a HRM and telling lots of lies).
for me it is a no brainer would never use a phone to track my ride, mainly because Iphone battery is so shite and frankly Garmins are so good. My devices fails never to connect. This is the post I refer to
http://keithhack.blogspot.co.uk/2016/11/why-hasnt-ant-been-crushed-by-bl...
I think I remember from a podcast of his that there are licensing and membership issues with ANT of something like £25k. That would be prohibitive to most startups.
with PM if cheap does it matter if accurate. As long as power is consistent then you measure yourself on that and if it is 50W out, who cares unless you comparing to others using 1K PM's ?
I'd want one if it works, but I'm somewhat sceptical. I don't see how it can measure cadence and I'd be surprised if the power "measurement" is accurate.
I think the idea is that it calculates power based on air pressure changes within the tyre - that is, you apply pressure to the pedals and that causes a small but measurable change in pressure within the tyre at the valve. Sort of like standing on a balloon, causing the balloon to deform. That means it does more than measure its own air speed or the rate at which the wheel moves (as others are suggesting). I assume that's how they detect cadence even though it only attaches to the front wheel - the cyclic nature of pressure change as you press the pedals is presumably used to infer how fast you're pedalling.
It seems like it would be fairly unreliable though. Surely hitting a bump in the road will cause similar changes in air pressure. I like the idea of a £100 power meter, but it just seems like it would be too unreliable by not directly measuring the force you exert.
Almost, you are heading in the right direction, but as described above you are endangering Newton's laws.
Overall force on the ground (total front and rear) can't change due to pedalling, 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.
Nope, there is not a direct realationship, there is a indeterminate coupling between the two, and that's why it could never work by measuring tyre pressure.
Using your analogy of the front wheel lifting off the road if you put power in, that's only true if you have your weight towards the rear of the bike, move your weight forward, you'll get a different reading, change the angle of your peak torque with respect to the ground and you'll get a different result. Put different forces through the bars, you'll get different results. Do pretty much anything and you'll get different results. At best all you could do woud be determine cadence.
I can also say from my day job, which has in the past involved developing electronics and software to produce a complete solution for the optical measurement of road surface roughness, that it's far easier to say "it's easy to filter out transients", than to actually filter out those transients
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