Speed non-zero while standing still

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Loek
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Speed non-zero while standing still

Post by Loek » Fri Dec 29, 2017 7:05 pm

Today I tried to do a short course. Before hitting the start button (see screenshot below), I drove the pedals a few times and then stopped pedaling. The power and cadence immediately went to zero as well (when the brake roller also stopped), but the speed still showed high values. The speed only dropped very slowly (for example after 10 seconds standing still, it still showed 13.8 km/h). Is this a known issue? The speed should show 0 km/h as soon as the brake roller stops, right?

Image

This was on a Genius Smart.
Last edited by Loek on Fri Dec 29, 2017 8:21 pm, edited 1 time in total.

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Alex Masalovich
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Re: Speed non-zero while standing still

Post by Alex Masalovich » Fri Dec 29, 2017 7:42 pm

Loek wrote:
Fri Dec 29, 2017 7:05 pm

Code: Select all

[img]https://lh3.googleusercontent.com/D37Oe9b-OSKzGbDdRUMtqcA2HJM4LCma2_JQ2YqM2Mh01qd0AQVEy-xGYqsvXUmJx4dgJfBwWH2ru-BPuXHt=w1920-h949-rw[/img]
Between the img tags there must be a URL of the picture that you can find by clicking on it with the right mouse button or by reading the html code of the page where the picture is located. For example:

Code: Select all

[img]http://www.google.com/images/errors/robot.png[/img]
Image
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Re: Speed non-zero while standing still

Post by Loek » Fri Dec 29, 2017 8:00 pm

Mm, strange. For me, the image shows without any issues. Anyway, here is a link to the image (I don't have a .jpg URL for this image): https://drive.google.com/file/d/1mIN7xO ... sp=sharing.

Another test: can you see the image below?

Image

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Re: Speed non-zero while standing still

Post by mcorn » Fri Dec 29, 2017 8:08 pm

Are you using any kind of additional speed sensor other than what is built into the Genius Smart?

Have you tried this with any other software, such as the other Tacx Android apps?

This might be a display bug in the app itself and not an issue with the brake.

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Re: Speed non-zero while standing still

Post by Alex Masalovich » Fri Dec 29, 2017 8:13 pm

Loek wrote:
Fri Dec 29, 2017 8:00 pm
Mm, strange. For me, the image shows without any issues. Anyway, here is a link to the image (I don't have a .jpg URL for this image): https://drive.google.com/file/d/1mIN7xO ... sp=sharing.
The URL does not need to have an extension .jpg
In this case, the code looks like this:

Code: Select all

[img]https://lh5.googleusercontent.com/LKysa1qtxlOvGFml_aO3uD7CuJT55qhQRyDrHR4XSLMPyIpSqFV8FFAiwcnH-_J-o0LKkanzmi8OEH-Szah9=w1656-h934[/img]
Access to the picture must be opened!
Loek wrote:
Fri Dec 29, 2017 8:00 pm
Another test: can you see the image below?
Yes.
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Re: Speed non-zero while standing still

Post by Loek » Fri Dec 29, 2017 8:19 pm

mcorn wrote:
Fri Dec 29, 2017 8:08 pm
Are you using any kind of additional speed sensor other than what is built into the Genius Smart?

Have you tried this with any other software, such as the other Tacx Android apps?

This might be a display bug in the app itself and not an issue with the brake.
No, I'm not using any other sensors, just the Genius itself. I'll test with the Utility app. Do you know of more Android apps where I can test with?
Last edited by Loek on Fri Dec 29, 2017 8:22 pm, edited 1 time in total.

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Re: Speed non-zero while standing still

Post by Loek » Fri Dec 29, 2017 8:20 pm

Alex Masalovich wrote:
Fri Dec 29, 2017 8:13 pm
Yes.
Thanks for checking :wink:.

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Re: Speed non-zero while standing still

Post by Alex Masalovich » Fri Dec 29, 2017 8:28 pm

Loek wrote:
Fri Dec 29, 2017 7:05 pm
Before hitting the start button (see screenshot below)
The values of these parameters outside the training frame (before and after the end) can indeed have such oddities.
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Re: Speed non-zero while standing still

Post by Loek » Fri Dec 29, 2017 8:29 pm

Loek wrote:
Fri Dec 29, 2017 8:19 pm
No, I'm not using any other sensors, just the Genius itself. I'll test with the Utility app. Do you know of more Android apps where I can test with?
Okay, I just tested with the 'Utility' app that shows the speed as well. In this app, the speed drops to zero as soon as the brake roller stops spinning. So the Utility app shows it correctly. Seems that it's the Android Training App which has the bug then. How should I report this to Tacx? Is posting this topic enough, or should I do more?

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Re: Speed non-zero while standing still

Post by Loek » Fri Dec 29, 2017 11:47 pm

Alex Masalovich wrote:
Fri Dec 29, 2017 8:28 pm
The values of these parameters outside the training frame (before and after the end) can indeed have such oddities.
I did some further testing. But not only before and after the end the speed is wrong; also during the activity, the speed shows non-zero values while standing still. See the screenshots below, during the activity. You can see that the power and cadence values show zero (correct), but for those periods of time the speed is non-zero and only slowly decreasing.

Image

When looking at the activity on Tacx Cloud, also the speed is shown incorrectly, see the screenshot below. So it seems that not only the visualization in the mobile app is wrong, but also the actual logging (hence Tacx Cloud also shows the wrong values when reviewing the activity). Hopefully this bug can be fixed soon.

Image.

Another example where the speed is wrong: this time when doing a .gpx ride on the mobile app.

Image

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Re: Speed non-zero while standing still

Post by Alex Masalovich » Sat Dec 30, 2017 6:07 pm

It looks like an incorrect imitation of inertia.
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Re: Speed non-zero while standing still

Post by Loek » Sat Dec 30, 2017 6:59 pm

Possibly, yes. I'll contact Tacx Support to mention this. Or do they also read these topics and no need to report also to Support?

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Re: Speed non-zero while standing still

Post by Alex Masalovich » Sat Dec 30, 2017 7:43 pm

Loek wrote:
Sat Dec 30, 2017 6:59 pm
Or do they also read these topics and no need to report also to Support?
They left this forum a long time ago.
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Re: Speed non-zero while standing still

Post by Loek » Sat Dec 30, 2017 7:46 pm

Ai, that's sad to hear. Thanks, then I'll contact them by email.

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Re: Speed non-zero while standing still

Post by GijsTacx » Mon Jan 08, 2018 12:00 pm

Gijs from the App Team here:

The reason you're seeing this behaviour has to do with Virtual Speed.

The app no longer reports the speed measured in the break itself, but also takes into account your weight, air resistance and, most relevant in this case, slope. Based on all these values the speed you would have while cycling on the road is simulated. In this case, you're heading down a .5% slope. Like in real life, if you'd stop pedaling, this means you will not stop immediately, as you're still "going down hill". I see a lot of confusion related to virtual speed and we should figure out how to explain it a bit better (as we don't really do so now) but the math is actually correct. We did test/calculate it multiple times and it does match what is expected, when considering proper physics.

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Re: Speed non-zero while standing still

Post by Alex Masalovich » Mon Jan 08, 2018 8:48 pm

It turns out that this is just a correct imitation of inertia.
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Re: Speed non-zero while standing still

Post by Loek » Mon Jan 08, 2018 10:52 pm

Hi Gijs, thanks for responding here. I did some further tests. And it indeed seems that the higher the percentage, the faster the speed goes to zero once stopping pedaling. So this part makes sense.

However, it does so very unrealistically. For example, on a 7% hill, it takes about 17(!) seconds before the speed is zero after stopping pedaling when going only 10 km/h. In reality, this would only take like 4 or 5 seconds at most I think. For a 1% slope it takes 23 seconds, and for an 11% slope, it takes 15(!) seconds according to the Android app. This is completely unrealistic, isn't it? The brake was calibrated and in the center (green) area.

When reviewing the activity on Tacx Cloud, the analysis graph shows different values for some reason. There, the time it takes to reach zero speed is much shorter, but still too long. For example, instead of 15s for an 11% hill, it still takes 8 seconds. It's lower, but still way too long.

So two issues still present it seems:

1. Mainly the Android app (but also on Tacx Cloud), the speed drops to zero too slowly, and is not realistic.
2. The values as shown 'live' on the Android app do not match with the analysis graph in Tacx Cloud.

If you need some further data (screen recordings/video), let me know what you need and I'll try to provide.

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Re: Speed non-zero while standing still

Post by Loek » Tue Jan 09, 2018 9:17 pm

I checked with some basic maths and physics (only taking into account gravitational force), and if I did the calculations right, it would only take about 2.6 seconds before one would come to a standstill after stopping pedaling from 10 km/h on an 11% slope. That's a lot shorter than 15 seconds... I was not even taking into account rolling resistance and air resistance, which would make the 2.6 seconds even shorter.
We did test/calculate it multiple times and it does match what is expected, when considering proper physics.
Not sure what physics you are using, but it might be good to have one more check :). Hopefully the issue can be solved so we have more realistic numbers. If you need more details on my calculations, let me know.

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Re: Speed non-zero while standing still

Post by Alex Masalovich » Wed Jan 10, 2018 11:26 am

On January 4, 2018, a new version of the Tacx Training app (3.0.27) was released. Did it change the situation somehow?
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Re: Speed non-zero while standing still

Post by Loek » Wed Jan 10, 2018 9:25 pm

No, latest tests were with that version. If I remember correctly, also with the older version I saw the same issue.

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