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Re: Velosense [motd2k] [ In reply to ]
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No, it is based on Doppler shift, but it is subject to the same sources of error (e.g., timing).

The bottom line is that GPS sucks for speed measurements. That's why you can't get decent field-test data using one for aero testing. That's also why you're calculated pace on a sports watch bounces around far more than reality when running.
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Re: Velosense [Slowman] [ In reply to ]
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This hysteresis of separation/reattachment is I think likely to be a significant issue and why we are interested in the wind yaw results we have been getting so far. I used to be a trackside aerodynamicist in F1 and we would measure pressures on parts of the car in real-time because we frequently saw this sort of issue, where they could have a significant effect. For example we would try to design the diffuser so it separates on the straight where the high speed, high downforce pushes the diffuser close to the ground in order to save drag. Trick is to have it reattach under braking when the rear lifts up again so the rear wheels have enough downforce to get round the corner. Occasionally this wouldnt happen because of this hysteresis, and at least twice I have seen high speed accidents where a driver has gone into a corner without any rear downforce due to this hysteresis and spun into the barriers.

This is a stark reminder that the wind tunnel is a model of reality and as Dan says misses many dynamics of cycling on the road.

So going back to the wind issue, it is likely that a fluctuating wind yaw angle produces a higher mean drag than a constant wind yaw angle if the fluctuations push the wheel over their separation angle. It is something that we can't easily study in the wind tunnel, so will be an interesting area to explore in road testing.

Real-world aero testing we believe is going to become very important in cycling aero - once we establish a level of confidence in our data, we can start looking at physical differences between the wind tunnel and the road.

We will post some of our real-time wind yaw data on this forum later today.
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Re: Velosense [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
No, it is based on Doppler shift, but it is subject to the same sources of error (e.g., timing).

The bottom line is that GPS sucks for speed measurements. That's why you can't get decent field-test data using one for aero testing. That's also why you're calculated pace on a sports watch bounces around far more than reality when running.

Respectfully, implemented correct (or even, reasonable correctly!), it really doesn't! Multipath and timing errors have very little impact on the Doppler shift.
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Re: Velosense [bgarrood] [ In reply to ]
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bgarrood wrote:
Hi Tom,

I'm Barney, cofounder of Velosense, and I was interested to see your data. I dont know the details of the sensor you used, but I think worth a few comments.

Of course wind varies massively by geographical position and current weather, so we can't say what the norm is, but we have seen substantial swings in yaw angle - we are putting together a graph similar to yours to show this, and will be similar to what we showed Dan at Interbike.

Clearly we arent measuring the same conditions, so we can't compare our results to yours directly, but worth considering what else may cause differences in our results.

Hi Barney,
That example I posted above was just a snippet of some data I have and was selected to show how it takes quite dramatic handlebar movements (turning into, and then out of, a low-speed, 180 degree turn) for the Aerostick to see what I would consider "wild" swings of measured yaw angle. It wasn't intended to be a summary of the typical ride data.

bgarrood wrote:
For our current development we are sampling at about 27Hz, which is as fast as we can log over Ant currently (Ant+ on a production unit would be substantially slower than this, perhaps 2-4Hz). This data seems to well resolve typical gusts, which can cause <1s fluctuations in wind speed and angle. At 27Hz we are getting multiple points through each cycle of the waveform. It looks like your data is at a much lower rate, perhaps 1Hz? If so, perhaps the Alphamantis sensor is internally doing some averaging across each time step, meaning it will smooth out these higher frequency fluctuations (if they indeed exist).

Yeah...that's what I was trying to explain. I don't know the details of the inner workings of the Alphamantis setup, and so those questions I have about averaging vs. downsampling (or whatever) are present. I also don't know if the app I'm using to record the results is doing so either. In the end, all I get is a 1Hz recorded .csv file.

bgarrood wrote:
This data is really byproduct of our main thrust of being able to accurately measure drag on the road, but it has (to our surprise) highlighted how large the fluctuations are that you can see, and so the importance of having a sensor whose yaw angle range covers those fluctuations if you are going to accurately measure the average wind.

As I said, John will post some of our data on this forum, and we will keep looking at this aspect of our data and posting our findings as we go. We are always interested to hear your thoughts.

That will be interesting to see, although what has been mentioned recently here on the forum is that "steady-state" wind tunnel data does quite a good job at modeling "outdoor" power demands, even when the outside riding is done under quite variable conditions.



As taken from this classic published study:
http://cdmbuntu.lib.utah.edu/utils/getf ... e/5200.pdf

As Andy Coggan likes to point out, that data implies that any additional drag caused by those yaw variations (and any separation/reattachment effects) would only account for ~3% of the total power demand at most.

In then end though, I completely agree that better measurement tools are always...well...better :-)

http://bikeblather.blogspot.com/
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Re: Velosense [Tom A.] [ In reply to ]
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Thanks Tom,
I agree with you that it is unlikely that these fluctuations are going to be a second order effect and are unlikely to undermine wind tunnel results. I think it will be interesting to see if those second order effects can make the difference between which set of wheel is best for a particular set of conditions for instance.
Last edited by: bgarrood: Oct 3, 18 11:58
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Re: Velosense [Tom A.] [ In reply to ]
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(Part 1)
Hello,
Here is a quick post to display some data taken on a day with wind generally below 5mph. The section of data taken is a hill we use for some testing which has hedgerows on each side. I have shown a trace of airspeed (in meter per second, absolute magnitude, not in direction of the bike) and yaw angle (degrees relative to the bike). I have included the raw sample rate which is 26 hz and a 1hz moving average. You can see that for this data the average yaw angle is close to zero, though brief spikes of crosswind of +/- 10 degrees.

The next picture will show a 5s zoom on the same plot.

You can see that the sensor can detect local spikes that a 1hz moving average will not detect.
The plot below shows a high crosswind condition between 11 to 14 degrees.

The following post will show what the speed and angle channels look like in the wind tunnel.

John Buckley
https://streamlines.aero
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Re: Velosense [John Buckley] [ In reply to ]
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(Part 2)
We can compare this to wind tunnel data which shows an angle sweep below, showing that in clean air the device signal is extremely stable.

Zooming in on an angle change, you can see the change between angles. Note that the windtunnel turntable does not move in an entirely smooth manner.


John Buckley
https://streamlines.aero
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Re: Velosense [Slowman] [ In reply to ]
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Slowman wrote:

i HATE that product. that isn't a steering damper. it's a steering inhibitor. but it does bring to mind something about steering geometry. i find that over the years a lot of bike makers think intuitively but in so doing choose a solution that requires counterintuitive thinking. the steering in tri bikes should not be slow. it should be reasonably quick. not superquick, road race quick, but semi-quick, as in 59mm to 60mm of trail. when you get buffeted, and have to countersteer to overcome a change in steering torque, you need to be able to react quickly. the bike needs to respond quickly.

it's intuitive to think that a quick responding bike is less stable, more prone to speed wobble, but i find that a system's stiffness is what avoids speed wobble, rather than its tendency to self-center thru jamming in a bunch of trail.

On the subject of speed wobbles...check this out: https://vimeo.com/213107209

That looks somewhat interesting as well...

http://bikeblather.blogspot.com/
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Re: Velosense [Tom A.] [ In reply to ]
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Tom A. wrote:
Slowman wrote:


i HATE that product. that isn't a steering damper. it's a steering inhibitor. but it does bring to mind something about steering geometry. i find that over the years a lot of bike makers think intuitively but in so doing choose a solution that requires counterintuitive thinking. the steering in tri bikes should not be slow. it should be reasonably quick. not superquick, road race quick, but semi-quick, as in 59mm to 60mm of trail. when you get buffeted, and have to countersteer to overcome a change in steering torque, you need to be able to react quickly. the bike needs to respond quickly.

it's intuitive to think that a quick responding bike is less stable, more prone to speed wobble, but i find that a system's stiffness is what avoids speed wobble, rather than its tendency to self-center thru jamming in a bunch of trail.


On the subject of speed wobbles...check this out: https://vimeo.com/213107209

That looks somewhat interesting as well...

i'm always interested in new products that fix problems. but i still maintain that if a system (frame, fork, stem, etc.) is sufficiently stiff, and the bike is made remotely properly, speed wobble shouldn't happen.

here's damon's famous speed wobble inducement video:



i wonder if cane creek resorted to this for their video? and what would happen if they did that same thing with the damping headset installed?

Dan Empfield
aka Slowman
Last edited by: Slowman: Oct 3, 18 15:04
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Re: Velosense [John Buckley] [ In reply to ]
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Very interesting! Thank you for sharing. Out of curiosity, what were approximate wind speeds in the "high crosswind" condition? 10-15mph?
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Re: Velosense [John Buckley] [ In reply to ]
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Yes. That's what I'm talking about. The known steady-state condition test (wind tunnel) implies that the measurements taken outside may have that actual variability.

Of course, your 1Hz averaged data now makes me wonder even more if the 1Hz data reported by the WASP utility app is averaged or sampled. If it's the former, then it means the Aerostick output is "smoothed"...but, if it's merely downsampled, then it wouldn't be that smoothed. I really need to see if I can find that out from NPE...

Now then...one other thing I was reminded of recently is that certain pressure sensors have some vibration sensitivity due to their construction. So then, my next question would be: How do we know we aren't seeing road vibration noise?

http://bikeblather.blogspot.com/
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Re: Velosense [Tom A.] [ In reply to ]
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Tom A. wrote:
Slowman wrote:


i HATE that product. that isn't a steering damper. it's a steering inhibitor. but it does bring to mind something about steering geometry. i find that over the years a lot of bike makers think intuitively but in so doing choose a solution that requires counterintuitive thinking. the steering in tri bikes should not be slow. it should be reasonably quick. not superquick, road race quick, but semi-quick, as in 59mm to 60mm of trail. when you get buffeted, and have to countersteer to overcome a change in steering torque, you need to be able to react quickly. the bike needs to respond quickly.

it's intuitive to think that a quick responding bike is less stable, more prone to speed wobble, but i find that a system's stiffness is what avoids speed wobble, rather than its tendency to self-center thru jamming in a bunch of trail.


On the subject of speed wobbles...check this out: https://vimeo.com/213107209

That looks somewhat interesting as well...

So... thick grease and some machining? Not a bad idea if it works.
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Re: Velosense [GreenPlease] [ In reply to ]
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GreenPlease wrote:
Tom A. wrote:
Slowman wrote:


i HATE that product. that isn't a steering damper. it's a steering inhibitor. but it does bring to mind something about steering geometry. i find that over the years a lot of bike makers think intuitively but in so doing choose a solution that requires counterintuitive thinking. the steering in tri bikes should not be slow. it should be reasonably quick. not superquick, road race quick, but semi-quick, as in 59mm to 60mm of trail. when you get buffeted, and have to countersteer to overcome a change in steering torque, you need to be able to react quickly. the bike needs to respond quickly.

it's intuitive to think that a quick responding bike is less stable, more prone to speed wobble, but i find that a system's stiffness is what avoids speed wobble, rather than its tendency to self-center thru jamming in a bunch of trail.


On the subject of speed wobbles...check this out: https://vimeo.com/213107209

That looks somewhat interesting as well...


So... thick grease and some machining? Not a bad idea if it works.

Damping plates and a "fluorocarbon gel" according to their literature...

http://bikeblather.blogspot.com/
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Re: Velosense [John Buckley] [ In reply to ]
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Thank you for sharing this data. I am looking forward to see more. I am extremely pleased with the fact you shared the context under which the data was collected. Data without context can be framed any which way we want and that's something nobody wants here.

I really like the product. Instant feedback is a nice feature and if I had a reliable number to look at while I race, it would without doubt be a motivator to maintain form.

With regards to discussions around the impact of a flatter yaw distribution, as well a the transient nature of airflow, be it environmental or rider based, we will find some gains there from an equipment perspective, but the real prize here is around the evaluation of impacts from a rider position, movement and skin suit design perspective.

On the road data collection is not a panacea, nor is WT testing, they both work together. What matters is that we can truthfully measure our observations of the world so that they can be replicated in a controlled environment. That's how we win.
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Re: Velosense [Tom A.] [ In reply to ]
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This is exactly what I was eluding to on the tweet to DCR. A wind tunnel can't make a good sensor look bad, but it can make a bad sensor look good.
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Re: Velosense [motd2k] [ In reply to ]
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You are totally right to question the effect of vibration on the sensors. Coming from an F1 background, which is an exceptionally challenging environment for vibration, we are particularly sensitive to this problem but have experience in mitigating the problems it presents.


We have done tests where we run several sensors in a sealed bottle on the bike to understand how real world vibration affects the sensor output. In the end we have chosen sensors with the lowest sensitivity to vibration that we could find, and mounted them in a way that mitigates what little vibration effect there is. We can say with confidence that these variations in flow velocity and yaw angle are not coming from the effect of vibration on the sensors.
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Re: Velosense [bgarrood] [ In reply to ]
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bgarrood wrote:
You are totally right to question the effect of vibration on the sensors. Coming from an F1 background, which is an exceptionally challenging environment for vibration, we are particularly sensitive to this problem but have experience in mitigating the problems it presents.


We have done tests where we run several sensors in a sealed bottle on the bike to understand how real world vibration affects the sensor output. In the end we have chosen sensors with the lowest sensitivity to vibration that we could find, and mounted them in a way that mitigates what little vibration effect there is. We can say with confidence that these variations in flow velocity and yaw angle are not coming from the effect of vibration on the sensors.

Excellent. Thanks for answering that!

http://bikeblather.blogspot.com/
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Re: Velosense [bgarrood] [ In reply to ]
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Just wanted to say thanks for coming on and answering these questions. We can be a tough group and it’s nice to see someone willing to go into the weeds answering questions, instead of the “trust us we know this stuff”, that we sometimes get.
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Re: Velosense [chicanery] [ In reply to ]
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Hello chicanery and All,

Interesting to see your comment about a yaw string (that is really old school, inexpensive, and low maintenance):

"Some of the best yaw data I have gathered is with string and a GoPro, as the string doesn't have a limitation on the angles it can express."

https://en.wikipedia.org/wiki/Yaw_string





Flight training in the T33 used a yaw string .... it worked great and seldom had maintenance problems.

How did you mount your yaw string and how did you record results?

After reading your comment I am going to add a yaw string to my bike to have a visual yaw reference .... now I need a simple way to measure pressure.

........ Or perhaps a different device than the string .... miniaturized to about the size of my thumb ... with a Garmin mount .... a lidar.

My cousin worked on some non classified devices at Aerospace Corp. that can identify different molecules at a distance (CO2 or toxic molecules for instance) and spoke about measuring wind speed and velocity at high altitudes from the ground ... or a sattelite.

A similar lidar could measure wind speed and velocity at different distances from the bicycle .... far enough away (a few feet or so ahead) to avoid localized effects of compression and perhaps reduce the inevitable changes induced when observing a phenomenon.

https://spectrum.ieee.org/...nd-speeds-from-space



Excerpt:

"It’s closing time for one of Earth observation’s most stubborn and critical data gaps: global wind speeds. A European Space Agency (ESA) satellite set for launch from French Guiana tomorrow—after nearly two decades of challenging engineering and a weather delay—will be the first to directly measure wind speed and direction, from Earth’s surface to the stratosphere.

Winds are key determinants of weather and climate, yet most wind data still comes from weather balloons. Readings from commercial jets supplement the balloons’ twice-daily samplings, along with estimates inferred from satellites that track moving clouds, atmospheric temperatures, and sea-surface roughness. The result is a patchy wind record that adds uncertainty to weather forecasts.

The new satellite, named Aeolus, will improve on these measurements by deploying a wind-sensing lidar in space for the first time. It is essentially the same light-pulsing object-detection technology that helps police enforce speed limits and autonomous vehicles navigate roads. But instead of detecting motion by pinging a car with laser light and measuring the Doppler shift in the photons reflected back, Aeolus will ping molecules and aerosols in the air from 320 kilometers above Earth."

https://arstechnica.com/...echnology-explained/


Excerpt:


"Lidar used to cost $75,000. Experts expect this to fall to less than $100."

Cheers, Neal

+1 mph Faster
Last edited by: nealhe: Oct 4, 18 19:49
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