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Introducing Arofly, “the world’s smallest power meter” + video

New valve mounted system weighs 10g and costs just £100

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.

Arofly - 4.jpg

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.

Arofly - 1.jpg

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.

Arofly - 2.jpg

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. We send him off around the world to get all the news from launches and shows too. 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

Avatar
janusz0 | 4 years ago
1 like

OK George, please show us graphs of simultaneous readings from an Arofly and a strain gauge powermeter on the same bicycle over a hilly course. (I wouldn’t  expect precise agreement, but would expect the integrated readings over the entire course to be close.)

Avatar
rkemb replied to janusz0 | 4 years ago
0 likes

janusz0 wrote:

OK George, please show us graphs of simultaneous readings from an Arofly and a strain gauge powermeter on the same bicycle over a hilly course. (I wouldn’t  expect precise agreement, but would expect the integrated readings over the entire course to be close.)

Like the ones in this review -- https://road.cc/content/review/227916-arofly-power-meter -- which appear to indicate that the basic concept doesn't work at all?

Avatar
janusz0 replied to rkemb | 4 years ago
0 likes

rkemb wrote:

janusz0 wrote:

OK George, please show us graphs of simultaneous readings from an Arofly and a strain gauge powermeter on the same bicycle over a hilly course. (I wouldn’t  expect precise agreement, but would expect the integrated readings over the entire course to be close.)

Like the ones in this review -- https://road.cc/content/review/227916-arofly-power-meter -- which appear to indicate that the basic concept doesn't work at all?

Thanks for the reminder rkemb.  I'd forgotten about that article!  It doesn't look good, but maybe George can point us at an up to date comparison.

Avatar
GeorgeWood | 4 years ago
0 likes

2019/5/6

Hi all, 

The AROFLY team has dedicated several experiments and tests to design the customized Sensors,Hardware and Integration of the exclusive software for the AROFLY system.

AROFLY’S dynamic air pressure system,is totally a”New Invention”. All the technology in hardware,software and algorithms had to be created from Zero. There is no similar technology and system of a power meter in the market to compare or learn from.

By accumulating information from several valuable experiments and tests,the AROFLY team identified the core value for the AROFLY power meter system.

After two full years of hard and dedicated work on more advanced technology,the AROFLY team developed,the ELITE,LINK and XELITE in 2019.

The first AROFLY model was designed in 2017. The AROFLY Sensor,worked in conjunction with a Smart Phone APP,using GPS for altitude and gradient.

The slow response of the required data from the Smart Phone was not good enough for the AROFLY sensor to identify the slope changes,causing late data output,thus confusing the cyclist.

We valued all the positive and negative feedback from the market,we listened to our customers very seriously. This feedback was discussed and has driven the AROFLY team to carry out more research,development and evaluation,to complete a new generation for AROFLY.

The following are the improvements to the New AROFLY generation,ELITE,LINK,and XELITE.

The AROFLY team,designed a highly sensitive pressure sensor with a MCU in the AROFLY sensor for the upgraded algorithm and filtering program,to remove interference from road conditions.
Designed a highly sensitive altimeter and GPS in the hardware,for quick response on slopes and gradient changes,to correct algorithm mode for data output.
Included additional sensors in the system as sensor fusion to collect more raw data of road condition and pedaling status,to assist the algorithm with quick & correct data output.
Integrated the system with more functions and riding data on the products
The “LINK”version,now offers a very affordable,Bluetooth & ANT + connectivity to other Bike Computers
The “ELITE”& XELITE versions now offers a very affordable bike computer,with all the features and benefits of the more expensive bike computers in the market.

These new improvements will add more accuracy,consistency and flexibility to the operation of the AROFLY new generation,ELITE,LINK and XELITE.  

The new product are estimated to launch June/July 2019.

Thank you for your reading.

 Team Arofly 

 

Arofly Outdoor:

https://youtube.com/watch?v=MF91PD8DrJo

Arofly Indoor:

https://youtube.com/watch?v=cil-Z0_fpFE

 

Arofly ELITE OPERATION:  

https://youtu.be/P_2U8pJyFU8

Arofly ELITE INSTALLATION:  https://youtu.be/btI-EBrjfi8

 

AROFLY

https://youtu.be/ZhMn7XAGYhk

 

Avatar
GeorgeWood | 4 years ago
0 likes

2019/5/6

Hi all, 

The AROFLY team has dedicated several experiments and tests to design the customized Sensors,Hardware and Integration of the exclusive software for the AROFLY system.

AROFLY’S dynamic air pressure system,is totally a”New Invention”. All the technology in hardware,software and algorithms had to be created from Zero. There is no similar technology and system of a power meter in the market to compare or learn from.

By accumulating information from several valuable experiments and tests,the AROFLY team identified the core value for the AROFLY power meter system.

After two full years of hard and dedicated work on more advanced technology,the AROFLY team developed,the ELITE,LINK and XELITE in 2019.

The first AROFLY model was designed in 2017. The AROFLY Sensor,worked in conjunction with a Smart Phone APP,using GPS for altitude and gradient.

The slow response of the required data from the Smart Phone was not good enough for the AROFLY sensor to identify the slope changes,causing late data output,thus confusing the cyclist.

We valued all the positive and negative feedback from the market,we listened to our customers very seriously. This feedback was discussed and has driven the AROFLY team to carry out more research,development and evaluation,to complete a new generation for AROFLY.

The following are the improvements to the New AROFLY generation,ELITE,LINK,and XELITE.

The AROFLY team,designed a highly sensitive pressure sensor with a MCU in the AROFLY sensor for the upgraded algorithm and filtering program,to remove interference from road conditions.
Designed a highly sensitive altimeter and GPS in the hardware,for quick response on slopes and gradient changes,to correct algorithm mode for data output.
Included additional sensors in the system as sensor fusion to collect more raw data of road condition and pedaling status,to assist the algorithm with quick & correct data output.
Integrated the system with more functions and riding data on the products
The “LINK”version,now offers a very affordable,Bluetooth & ANT + connectivity to other Bike Computers
The “ELITE”& XELITE versions now offers a very affordable bike computer,with all the features and benefits of the more expensive bike computers in the market.

These new improvements will add more accuracy,consistency and flexibility to the operation of the AROFLY new generation,ELITE,LINK and XELITE.  

The new product are estimated to launch June/July 2019.

Thank you for your reading.

 Team Arofly 

 

Arofly Outdoor:

https://youtube.com/watch?v=MF91PD8DrJo

Arofly Indoor:

https://youtube.com/watch?v=cil-Z0_fpFE

 

Arofly ELITE OPERATION:  

https://youtu.be/P_2U8pJyFU8

Arofly ELITE INSTALLATION:  https://youtu.be/btI-EBrjfi8

 

AROFLY

https://youtu.be/ZhMn7XAGYhk

 

Avatar
GeorgeWood | 4 years ago
0 likes

2019/5/2
Hi all, 
The AROFLY team has dedicated several experiments and tests to design the customized Sensors, Hardware and Integration of the exclusive software for the AROFLY system.

AROFLY’S dynamic air pressure system, is totally a” New Invention”. All the technology in hardware, software and algorithms had to be created from Zero. There is no similar technology and system of a power meter in the market to compare or learn from.

By accumulating information from several valuable experiments and tests, the AROFLY team identified the core value for the AROFLY power meter system.

After two full years of hard and dedicated work on more advanced technology, the AROFLY team developed, the ELITE, LINK and XELITE in 2019.

The first AROFLY model was designed in 2017. The AROFLY Sensor, worked in conjunction with a Smart Phone APP, using GPS for altitude and gradient.
The slow response of the required data from the Smart Phone was not good enough for the AROFLY sensor to identify the slope changes, causing late data output, thus confusing the cyclist.

We valued all the positive and negative feedback from the market, we listened to our customers very seriously. This feedback was discussed and has driven the AROFLY team to carry out more research, development and evaluation, to complete a new generation for AROFLY.

The following are the improvements to the New AROFLY generation, ELITE, LINK, and XELITE.

1. The AROFLY team, designed a highly sensitive pressure sensor with a MCU in the AROFLY sensor for the upgraded algorithm and filtering program, to remove interference from road conditions.
2. Designed a highly sensitive altimeter and GPS in the hardware, for quick response on slopes and gradient changes, to correct algorithm mode for data output.
3. Included additional sensors in the system as sensor fusion to collect more raw data of road condition and pedaling status, to assist the algorithm with quick & correct data output.
4. Integrated the system with more functions and riding data on the products
5. The “ LINK” version, now offers a very affordable, Bluetooth & ANT + connectivity to other Bike Computers
6. The “ELITE” & XELITE versions now offers a very affordable bike computer, with all the features and benefits of the more expensive bike computers in the market.

These new improvements will add more accuracy, consistency and flexibility to the operation of the AROFLY new generation, ELITE, LINK and XELITE.  

The new product are estimated to launch June/July 2019.

Thank you for your reading.
 Team Arofly 

Arofly Outdoor:
https://youtube.com/watch?v=MF91PD8DrJo
Arofly Indoor:
https://youtube.com/watch?v=cil-Z0_fpFE

Arofly ELITE OPERATION:  
https://youtu.be/P_2U8pJyFU8
Arofly ELITE INSTALLATION:  https://youtu.be/btI-EBrjfi8

AROFLY
https://youtu.be/ZhMn7XAGYhk

Avatar
dwbeever | 7 years ago
0 likes

....all i need now, is to see release date of April 1st and my decision is made!

 

Avatar
asdfqwerty | 7 years ago
0 likes

The pressure sensor can be reprogrammed while in use to set a new pressure baseline, so that 1 bar range could be intended to just cover the small range of pressure variation at the valve as the tyre rotates. But, the absolute maximum pressure for the sensor is only 5 bar (72 psi), so it's not clear if it would cope with the higher pressures used in road tyres, or if it would fail to function. (as mentioned by someone else earlier, these sensors often operate outside of their rated operational bounds - the manufacture themselves have listed this in the datasheet as the upper limit). Anyway, proof is in the pudding, maybe DC Rainmaker will get his hands on one...

Avatar
Griff500 replied to asdfqwerty | 7 years ago
0 likes

asdfqwerty wrote:

Anyway, proof is in the pudding, maybe DC Rainmaker will get his hands on one...

Apparently it is only being released to the market in February 2017. This can go one of two ways: If it works as advertised, we will very soon see these things everywhere. If it doesn't, we will never hear of it again. Personally, I will watch what happens with the greatest of interest, and will happily part with my £100 if it works. But I certainly won't be at the head of the queue.

Avatar
jerome | 7 years ago
0 likes

OK not completely away  3

The pictures in the FCC submission clearly show a hole and a dent to depress the valve (saw that on another forum). So here is my new guess: the device actually measures tire pressure, as a mean to measure barometric pressure. This is the way they found to protect the pressure sensor, that would otherwise be exposed to water as soon as you run in a puddle. When barometric pressure drops, the tire enveloppe slighly swells and the pressure drops into the tire drops. I do not the relation between the pressure inside the tire and the pressure outside, but maybe it is close enough to 1:1 on that rather small range. As Griff500 rightly pointed out, the FBM320 has an absolute max rating of 10 bars, so they probably asked for a custom version with different gain/offset before ADC. They have to average the pressure over maybe 10s to keep only long term variations.

So to summarize: change of cyclist altitude causes change of barometric pressure, reflected by a change in tire pressure. That give a rate of climb/descent, and along with cc+bike weight gives one part of power. The other part of power required to overcome aerodynamic forces is estimated with cc speed, with is derived from the centripetal acceleration.

'hope this is not a too long and speculative post  3

Avatar
Griff500 replied to jerome | 7 years ago
0 likes

jerome wrote:

OK not completely away  3

The pictures in the FCC submission clearly show a hole and a dent to depress the valve (saw that on another forum). So here is my new guess: the device actually measures tire pressure, as a mean to measure barometric pressure. This is the way they found to protect the pressure sensor, that would otherwise be exposed to water as soon as you run in a puddle. When barometric pressure drops, the tire enveloppe slighly swells and the pressure drops into the tire drops. I do not the relation between the pressure inside the tire and the pressure outside, but maybe it is close enough to 1:1 on that rather small range. As Griff500 rightly pointed out, the FBM320 has an absolute max rating of 10 bars, so they probably asked for a custom version with different gain/offset before ADC. They have to average the pressure over maybe 10s to keep only long term variations.

So to summarize: change of cyclist altitude causes change of barometric pressure, reflected by a change in tire pressure. That give a rate of climb/descent, and along with cc+bike weight gives one part of power. The other part of power required to overcome aerodynamic forces is estimated with cc speed, with is derived from the centripetal acceleration.

'hope this is not a too long and speculative post  3

Inventing things again? Griff500 never mentioned 10 bars anywhere, he said the supplier only rates it as far as 15psi, which is 1 Bar.

Also, as  I have been at pains to point out, the manufacturer clearly states that the device measures "the reaction force from the ground".  You seem to be telling him he is wrong and it works in a totally different way!

You will also have great difficulty getting a value for the elasticity of the tyre/tube combination, which determines the relationship between internal and external pressure.  1:1, that's a joke. How would the tyre hold 100psi if it has a 1:1 pressure relationship to the outside!

Then of course there is the not inconsiderable problem that changes in tyre pressure due to pedal power changes (the bit that Arofly have told us they measure) are much greater than the altitude related changes you are trying to measure, and will totally mnask your altitude effect.

Avatar
davel replied to Griff500 | 7 years ago
1 like
Griff500 wrote:

jerome wrote:

OK not completely away  3

The pictures in the FCC submission clearly show a hole and a dent to depress the valve (saw that on another forum). So here is my new guess: the device actually measures tire pressure, as a mean to measure barometric pressure. This is the way they found to protect the pressure sensor, that would otherwise be exposed to water as soon as you run in a puddle. When barometric pressure drops, the tire enveloppe slighly swells and the pressure drops into the tire drops. I do not the relation between the pressure inside the tire and the pressure outside, but maybe it is close enough to 1:1 on that rather small range. As Griff500 rightly pointed out, the FBM320 has an absolute max rating of 10 bars, so they probably asked for a custom version with different gain/offset before ADC. They have to average the pressure over maybe 10s to keep only long term variations.

So to summarize: change of cyclist altitude causes change of barometric pressure, reflected by a change in tire pressure. That give a rate of climb/descent, and along with cc+bike weight gives one part of power. The other part of power required to overcome aerodynamic forces is estimated with cc speed, with is derived from the centripetal acceleration.

'hope this is not a too long and speculative post  3

Inventing things again? Griff500 never mentioned 10 bars anywhere, he said the supplier only rates it as far as 15psi, which is 1 Bar.

Also, as  I have been at pains to point out, the manufacturer clearly states that the device measures "the reaction force from the ground".  You seem to be telling him he is wrong and it works in a totally different way!

You will also have great difficulty getting a value for the elasticity of the tyre/tube combination, which determines the relationship between internal and external pressure.  

 

Griff500 posted this. Has Griff500 been busted using multiple logins, or does Griff500 usually refer to himself in the 3rd person?

davel would like to know.

Avatar
Griff500 replied to davel | 7 years ago
0 likes

davel wrote:

Griff500 posted this. Has Griff500 been busted using multiple logins, or does Griff500 usually refer to himself in the 3rd person? davel would like to know.

No, not usually, just this once  

I am thinking of holding a discussion with myself though, because i'd get more sense out of me than out of Jerome

Avatar
jerome | 7 years ago
0 likes

"the additional complexity of a 670mm or so cyclic change of height"

Which is easily filtered, did not you mention that already?

"If you were using that to measure acceleration, why have it rotating?"

Because you obtain speed directly and all times when substracting gravity: a = g + V^2 / R

No need for integration which would lead huge errors over time. Dead simple.

"the Arofly press release" you keep giving more faith to those Taiwanese bullsh*ters than to your own jugement.

"measuring tyre pressure" which is a dead end you admitted it.

"remarkably close results, except when there is wind" so you admit my theory is valid

"weight figures or wheel sizes" are obviously required

Got fed up of that discussion. Byebye.

Avatar
jerome | 7 years ago
0 likes

I did not mean to be offensive (not native english speaker BTW), just to tell that lenghty speculative posts (not yours in particular) lead to nowhere. There is only one way we can see the device work right now (assuming it works) and this is not by measuring tire pressure, but measuring rate of climb/descent and guesstimating aerodynamic forces.

Avatar
Griff500 replied to jerome | 7 years ago
0 likes

jerome wrote:

I did not mean to be offensive (not native english speaker BTW), just to tell that lenghty speculative posts (not yours in particular) lead to nowhere. There is only one way we can see the device work right now (assuming it works) and this is not by measuring tire pressure, but measuring rate of climb/descent and guesstimating aerodynamic forces.

Sorry, I don't believe the climb / descent theory for one minute. If all you were doing was measuring altitude, why on earth would you mount the sensor on the wheel and have the additional complexity of a 670mm or so cyclic change of height?  Then of course there is the accelerometer. If you were using that to measure acceleration, why have it rotating?  You'd spend a lot of processing power just figuring out which way is up and which way is forward. These points, plus the fact that the Arofly press release I quoted says they are measuring tyre pressure, and the clear description they give of power measurement being a function of reaction against the ground, seem very clear. 

Strava already does exactly what you say based on digital map data, and does it well. Comparing my sector times with guys with power meters give remarkably close results, except when there is wind, which for Scottish cyclists like myself can sap as much power as hills. 

The App set-up sheds no light  the issue. They talk of switching from bike to bike and simply booting up bluetooth, yet there is no mention of providing weight figures or wheel sizes, or calibration. 

 

Avatar
jerome | 7 years ago
0 likes

"What, no retraction of the smartass "got it?"  comment?"

Nop, not till you explain how you measure force (required for power) with only pressure.

Avatar
Griff500 replied to jerome | 7 years ago
0 likes

jerome wrote:

"What, no retraction of the smartass "got it?"  comment?"

Nop, not till you explain how you measure force (required for power) with only pressure.

 

No idea. Been wondering myself.

I'm just the guy whose researched what little there is out there on this and tried to correct a misconception. The insults are totally unjustified, but if you want to stand by your post, so be it.

Avatar
jerome | 7 years ago
1 like

Would you trust the marketing blob or the schematic/datasheet? They also mention a Pitot but there is no need for a Pitot to measure air pressure in the chamber, where there is no wind AFAIK.

"It is very common in novel applications [...] to personally test and characterise the component" not when there are components readily available, or when you overshoot the specified range 6 folds.

Avatar
Griff500 replied to jerome | 7 years ago
0 likes

What, no retraction of the smartass "got it?"  comment?

jerome wrote:

Would you trust the marketing blob or the schematic/datasheet?

"It is very common in novel applications [...] to personally test and characterise the component" not when there are components readily available, or when you overshoot the specified range 6 folds.

Neither. I'd trust the test I would do myself, and I've done similar things a number of times, sometimes in high reliability high accuracy applications.

This is often a matter of component manufacturers testing and underwriting against the standard commercial component standards and intended use, rather than going to the expense of testing to a range where the component is not envisaged to be used. If I am selling a barometer chip, why would I test and underwrite its performance to 110psi?

I'm not an expert on silicon pressure sensors, but a bit of basic research comes up with comments about the diaphragms used being not only resistant to extreme overpressure, but remaining perfectly elastic and relatively linear up to the point of fracture. Which kinda suggests if it doesn't break, you will get some sort of sense out of it. (This is very different to overtemperature where at 125 degC or so things can rapidly start to go off a cliff.) There is no point us  guessing if its good enough, because we have neither the data, nor the detailed knowledge of the algorithm or implementation these guys use.

Avatar
Griff500 replied to jerome | 7 years ago
0 likes

jerome wrote:

They also mention a Pitot but there is no need for a Pitot to measure air pressure in the chamber, where there is no wind AFAIK.

Nowhere does it say there is a pitot tube. They say the sensor is based on F117 pitot tube technology, because pitot tubes are required measure small relative pressure changes!  They presumably mean an integrated pressure sensor, a/d convertor signal processor and serial bus on a chip as opposed to the old days of analogue pressure sensors in pitot tubes. (Your bike manufacturer may well brag about his aerospace grade carbon fibre, but it doesn't mean your bike will fly!)

Avatar
jerome | 7 years ago
0 likes

To all those having a degree in anything: the pressure sensor does not measure tire pressure, and does not claim to. First, because it cannot do it (someone checked the datasheet), second because in order to convert it to a force, I would require the area of the tire patch. Anyone to measure the tire patch realtime?

As mentionned above by IanMunro and others: the pressure sensor measure barometric pressure and infers a rate of climb together with speed, known with the accelerometer.

Got it?

Avatar
Griff500 replied to jerome | 7 years ago
0 likes

jerome wrote:

To all those having a degree in anything: the pressure sensor does not measure tire pressure, and does not claim to. First, because it cannot do it (someone checked the datasheet), second because in order to convert it to a force, I would require the area of the tire patch. Someone to measure the tire patch realtime?

As mentionned above by IanMunro and others: the pressure sensor measure barometric pressure and infers a rate of climb together with speed, known with the accelerometer.

Got it?

"Ian Munro and others" clearly didn't read the Arofly blurb before guessing how it works.

Quote Arofly:

Algorithm and calibration technology

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.”

"

Yes, I agree it sounds like BS, but let's see where they go with this.

It was me who checked the data sheet for the pressure sensor, and although as I said, it is only rated up to 15psi, that does not mean it turns into a pumpkin at higher pressures. It is very common in novel applications (Oil & Gas, process plants, miltary, submarine, polar exploration etc) to use an electronic component outwith the manufacturers rated range. It usually requires the designer to personally test and characterise the component under the conditions he intends to use it under.

Avatar
nowasps | 7 years ago
4 likes

I have a 25yds Swimming Certificate, and I have to say I quite like the knurling.

Avatar
IanMunro | 7 years ago
1 like

As noted by others, this product is complete bollocks.
There's no pitot tube in it, nor any reason it would have one.

It measures atmospheric air pressure to determine your rate of climbing or descending, and it measures wheel RPM to get velocity.
From these two variables and user entered data for weight, it will be guestimating what your power output is.
Strava will produce just an accurate result, but without this lump of tat stuck on your valve.

Avatar
tonyleatham | 7 years ago
3 likes

First off, I graduated with a degree in electronics in 1988 so I can read a schematic with the best of them. I can also watch a video. And having watched the video on the aerofly website which claims that the unit can measure heart rate, and that it could be adopted by "commuting students" I'm really not sure.

I once got the job of designing a gadget to determine how many paintballs a paintball gun could fire by analysing pressure variations in the compressed air cylinder used to propel the balls out the gun. It took a SERIOUS amount of doing and I had the advantage of being able to easily isolate the pressure change caused by firing the ball from background variations a) because the pressure change was sizable and b) there were no background variations. 

It took us a long time to get this right and we had to do some pretty fancy stuff in the end to compensate for temperature changes - the number we calculated was reliably within 10% of the actual number of paintballs the air in the tank could actually fire.

This aerofly device claims a massive operating temperature range and I just find it hard to believe that it's possible to pick out variations in pressure caused by application of force to the pedal from background variations caused by uneven road surfaces, pressure changes caused by heating and cooling of the braking surface etc. etc. I'm also not at all sure that you can reliably translate this into a meaningful power measurement. Potentially possible to get a relative measure (i.e. "you're pedalling harder now than you were"), but I'd not even bet on that.

I'm pretty sure that it's beyond my capabilities to design this device and get it working reliably to a point I'd by happy with.

 

Avatar
Griff500 replied to tonyleatham | 7 years ago
0 likes

tonyleatham wrote:

 

This aerofly device claims a massive operating temperature range and I just find it hard to believe that it's possible to pick out variations in pressure caused by application of force to the pedal from background variations caused by uneven road surfaces, pressure changes caused by heating and cooling of the braking surface etc. etc. I'm also not at all sure that you can reliably translate this into a meaningful power measurement. Potentially possible to get a relative measure (i.e. "you're pedalling harder now than you were"), but I'd not even bet on that.

I'm pretty sure that it's beyond my capabilities to design this device and get it working reliably to a point I'd by happy with.

 

While you were playing with toys, I was doing miltary signal processing.

To be fair, the FBM320 pressure sensor used appears to be noted for it's onboard temperature compensation capabilities. The fact it is only rated up to 15psi does however question how accurate it would be at the 90-100psi region many of us run our tyres at.

As for differentiating between road surface vibrations and pedal stroke?  Most road vibration is in the 10's of Hz range and random in nature. Power variation due to pedalling at a cadence of up to 90, would produce periodic variations of 0-3 Hz.  Any electronics or physics undergraduate could design a digital filter to cope with that in the timeframe of an exam question! Remember also that a conventional crank mounted pressure sensor already needs to be able to filter out a the vibration not filtered out by tyre and frame, (the lowest frequency stuff closest to pedal cycle in frequency) so filtering is still necessary here.

So assuming you could get the pressure reading, the signal processing is trivial.  The Pressure sensor used however doesn't appear to be up to use anywhere near tyre pressures.

Incidentally, for those arguing Ant versus BLE, the schematic also shows Ant2.

 

 

Avatar
tonyleatham replied to Griff500 | 7 years ago
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Griff500 wrote:

tonyleatham wrote:

 

This aerofly device claims a massive operating temperature range and I just find it hard to believe that it's possible to pick out variations in pressure caused by application of force to the pedal from background variations caused by uneven road surfaces, pressure changes caused by heating and cooling of the braking surface etc. etc. I'm also not at all sure that you can reliably translate this into a meaningful power measurement. Potentially possible to get a relative measure (i.e. "you're pedalling harder now than you were"), but I'd not even bet on that.

I'm pretty sure that it's beyond my capabilities to design this device and get it working reliably to a point I'd by happy with.

 

While you were playing with toys, I was doing miltary signal processing.

To be fair, the FBM320 pressure sensor used appears to be noted for it's onboard temperature compensation capabilities. The fact it is only rated up to 15psi does however question how accurate it would be at the 90-100psi region many of us run our tyres at.

As for differentiating between road surface vibrations and pedal stroke?  Most road vibration is in the 10's of Hz range and random in nature. Power variation due to pedalling at a cadence of up to 90, would produce periodic variations of 0-3 Hz.  Any electronics or physics undergraduate could design a digital filter to cope with that in the timeframe of an exam question! Remember also that a conventional crank mounted pressure sensor already needs to be able to filter out a the vibration not filtered out by tyre and frame, (the lowest frequency stuff closest to pedal cycle in frequency) so filtering is still necessary here.

So assuming you could get the pressure reading, the signal processing is trivial.  The Pressure sensor used however doesn't appear to be up to use anywhere near tyre pressures.

Incidentally, for those arguing Ant versus BLE, the schematic also shows Ant2.

 

 

I'm quite happy admitting that this device is not something I could design - I speak from experience of having worked on something similar. Part of the reason I think it's incredibly complicated is that the amplitude of the pressure variation caused by pedalling I suspect is incredibly small and in the real world, all assumptions about what can and can't be filtered usually don't survive the first test. Add to that the conversion time of the sensor is pretty slow (of the order of normal pedalling cadence), and I just don't think it's possible with this circuit.

You may scoff at my non-military experience, but I've worked both in defence (BAe) and consumer electronics, and by far the best people I worked with were outside of defence. 

If you feel it's something you could make work, do it and I'll buy one off you for $129.

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Griff500 replied to tonyleatham | 7 years ago
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tonyleatham wrote:

Griff500 wrote:

tonyleatham wrote:

 

This aerofly device claims a massive operating temperature range and I just find it hard to believe that it's possible to pick out variations in pressure caused by application of force to the pedal from background variations caused by uneven road surfaces, pressure changes caused by heating and cooling of the braking surface etc. etc. I'm also not at all sure that you can reliably translate this into a meaningful power measurement. Potentially possible to get a relative measure (i.e. "you're pedalling harder now than you were"), but I'd not even bet on that.

I'm pretty sure that it's beyond my capabilities to design this device and get it working reliably to a point I'd by happy with.

 

While you were playing with toys, I was doing miltary signal processing.

To be fair, the FBM320 pressure sensor used appears to be noted for it's onboard temperature compensation capabilities. The fact it is only rated up to 15psi does however question how accurate it would be at the 90-100psi region many of us run our tyres at.

As for differentiating between road surface vibrations and pedal stroke?  Most road vibration is in the 10's of Hz range and random in nature. Power variation due to pedalling at a cadence of up to 90, would produce periodic variations of 0-3 Hz.  Any electronics or physics undergraduate could design a digital filter to cope with that in the timeframe of an exam question! Remember also that a conventional crank mounted pressure sensor already needs to be able to filter out a the vibration not filtered out by tyre and frame, (the lowest frequency stuff closest to pedal cycle in frequency) so filtering is still necessary here.

So assuming you could get the pressure reading, the signal processing is trivial.  The Pressure sensor used however doesn't appear to be up to use anywhere near tyre pressures.

Incidentally, for those arguing Ant versus BLE, the schematic also shows Ant2.

 

 

I'm quite happy admitting that this device is not something I could design - I speak from experience of having worked on something similar. Part of the reason I think it's incredibly complicated is that the amplitude of the pressure variation caused by pedalling I suspect is incredibly small and in the real world, all assumptions about what can and can't be filtered usually don't survive the first test. Add to that the conversion time of the sensor is pretty slow (of the order of normal pedalling cadence), and I just don't think it's possible with this circuit.

You may scoff at my non-military experience, but I've worked both in defence (BAe) and consumer electronics, and by far the best people I worked with were outside of defence. 

If you feel it's something you could make work, do it and I'll buy one off you for $129.

Sorry about the scoff, but when someone opens a post by stating " I have a degree", they are setting themselves up!
I never said I could make it work for the price and size, I said the theory works but it's the wrong sensor. Read my post!

As for the pressure change being 'incredibly small", it is exactly the same change conventional power metres measure at the crank, you are just measuring it at a different point in the system. (Back to Newton 3rd).

Avatar
tonyleatham replied to Griff500 | 7 years ago
1 like

Griff500 wrote:
tonyleatham wrote:

Griff500 wrote:

tonyleatham wrote:

 

This aerofly device claims a massive operating temperature range and I just find it hard to believe that it's possible to pick out variations in pressure caused by application of force to the pedal from background variations caused by uneven road surfaces, pressure changes caused by heating and cooling of the braking surface etc. etc. I'm also not at all sure that you can reliably translate this into a meaningful power measurement. Potentially possible to get a relative measure (i.e. "you're pedalling harder now than you were"), but I'd not even bet on that.

I'm pretty sure that it's beyond my capabilities to design this device and get it working reliably to a point I'd by happy with.

 

While you were playing with toys, I was doing miltary signal processing.

To be fair, the FBM320 pressure sensor used appears to be noted for it's onboard temperature compensation capabilities. The fact it is only rated up to 15psi does however question how accurate it would be at the 90-100psi region many of us run our tyres at.

As for differentiating between road surface vibrations and pedal stroke?  Most road vibration is in the 10's of Hz range and random in nature. Power variation due to pedalling at a cadence of up to 90, would produce periodic variations of 0-3 Hz.  Any electronics or physics undergraduate could design a digital filter to cope with that in the timeframe of an exam question! Remember also that a conventional crank mounted pressure sensor already needs to be able to filter out a the vibration not filtered out by tyre and frame, (the lowest frequency stuff closest to pedal cycle in frequency) so filtering is still necessary here.

So assuming you could get the pressure reading, the signal processing is trivial.  The Pressure sensor used however doesn't appear to be up to use anywhere near tyre pressures.

Incidentally, for those arguing Ant versus BLE, the schematic also shows Ant2.

 

 

I'm quite happy admitting that this device is not something I could design - I speak from experience of having worked on something similar. Part of the reason I think it's incredibly complicated is that the amplitude of the pressure variation caused by pedalling I suspect is incredibly small and in the real world, all assumptions about what can and can't be filtered usually don't survive the first test. Add to that the conversion time of the sensor is pretty slow (of the order of normal pedalling cadence), and I just don't think it's possible with this circuit.

You may scoff at my non-military experience, but I've worked both in defence (BAe) and consumer electronics, and by far the best people I worked with were outside of defence. 

If you feel it's something you could make work, do it and I'll buy one off you for $129.

Sorry about the scoff, but when someone opens a post by stating " I have a degree", they are setting themselves up! I never said I could make it work for the price and size, I said the theory works but it's the wrong sensor. Read my post! As for the pressure change being 'incredibly small", it is exactly the same change conventional power metres measure at the crank, you are just measuring it at a different point in the system. (Back to Newton 3rd).

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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