Golden Cheetah in train mode always reading about 20 watts higher than Garmin

[Jamil Shehadeh]

I've done loads of searches on this but I can't find anyone else who has the same problem.

When I use Golden Cheetah in train mode, the power reading in CG is always about 20 watts higher than what my Garmin displays. And it's always about 20w rather than a percentage - so at 350w on the Garmin, GC reads about 370w, and at 150w on the Garmin, CG reads 170w.

The power is coming from an SRM power meter via Ant+ to my PC. I believe the Garmin is correct, because I can hold 350w for 4 mins, 370 I really can't :)

I took 4 photos to show what I mean, below. They're a bit blurry but you'll you can see the power difference (bottom right on the Garmin screen, top left on the PC)

https://photos.app.goo.gl/t22Q5hxQnb1QKrJk7

I can't find a setting in GC to reduce the power reading by a certain wattage in live training mode, and of course Edit - Adjust Power Values has no effect here because it's not intended for this.

I can live with it but it would be nice to be able to sit at the target wattage when training. I could increase the FTP to suit but then I'd be always looking at the wrong number all the time and I'd start getting the wrong idea... Or I could remove the current power reading in GC and just check the Garmin.

First World problems, eh...

[Claus Assmann (please do not Cc me)]

On Wed, Mar 13, 2019, Jamil Shehadeh wrote:

> When I use Golden Cheetah in train mode, the power reading in CG is always
> about 20 watts higher than what my Garmin displays. And it's always about

> The power is coming from an SRM power meter via Ant+ to my PC. I believe

Did you "calibrate" (set the zero offset) of the SRM in GC?
I'm not sure if that functionality is in the official build
(I wrote my own patch)

[Jamil Shehadeh]

Thanks, Claus.

Of course, that would fix it. But it doesn't seem to be possible in the standard build yet.

[Jamil Shehadeh]

Golden Cheetah would seem to be the perfect combination of computing and cycling. Sadly I wouldn't know how to start writing a patch...

Could someone point me in the right direction?

Cheers.

[Claus Assmann (please do not Cc me)]

On Sat, Mar 16, 2019, Jamil Shehadeh wrote:

> Golden Cheetah would seem to be the perfect combination of computing and
> cycling. Sadly I wouldn't know how to start writing a patch...

Patches for this exist, you don't need to write another one.
Search this mailing list ("forum") for these Subject:s

SRM autozero
manual calibration of SRM

and you will find the patches or links to github
(AFAIR the patch from Jon Escombe has been merged
into the official version, but I might be wrong).

[Ale Martinez]

This one https://github.com/GoldenCheetah/GoldenCheetah/commit/dbf3bab104f7a16e3d70cbdc3ebe8c7b2dd3635c#diff-f1c799435656e5ab4a3e6f7c70912e40 is present in current v3.5 development builds

[Jamil Shehadeh]

Thanks, both.

But I'm such a noob, I don't know how to get the files I need nor where to put them, and I can't see the option to calibrate an SRM in any of the options.

I've got V3.5 DEV1903 on Window 10.

Jamil.

[Claus Assmann (please do not Cc me)]

On Sun, Mar 17, 2019, Jamil Shehadeh wrote:

> But I'm such a noob, I don't know how to get the files I need nor where to

As you quoted in full below:

> > https://github.com/GoldenCheetah/GoldenCheetah/commit/dbf3bab104f7a16e3d70cbdc3ebe8c7b2dd3635c#diff-f1c799435656e5ab4a3e6f7c70912e40
> > is present in current v3.5 development builds

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> I've got V3.5 DEV1903 on Window 10.

So you should have it already (if "DEV1903" is "current").

Check the list of "buttons" (play/pause, fast forward, etc). There
should be one to "calibrate" ("mouse over" hopefully shows the
purpose of each "button")

[Jamil Shehadeh]

Ah, ok. I could be the up and down arrows at the end of the line of control buttons. The next time I'm on that PC I'll have a look.

Thanks again.

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[Jamil Shehadeh]

I found the spanner icon that is meant to do the calibration but it just seems to hang with this message (I waited 10 minutes):

Calibrating...
Unclip or stop pedalling until the process is complete
Torque 0.000

I read somewhere that there's usually a message to pedal then stop pedalling. I didn't get any of that.

I have a 5yr old SRM crankset power meter and I'm on the Feb 22 2019 build.

[alans...@gmail.com]

Hi did you ever find a solution to this? Regards alan

[Ale Martinez]

To calibrate your SRM in Train mode click the wrench icon in Train bottom bar and follow the indications displayed at the notifications panel

[jamils...@gmail.com]

@ Alan - I didn't fix this, but for a while I got a correct reading from my other power meter (I have two second hand SRMs, both about 10 years old - both work fine on the road and on Zwift. And if you have the patience, you can solder in new batteries yourself!).

For a month or two I was getting a very good reading on GC and Garmin on my other PM but one evening, when calibrating the SRM on the Garmin (which I do every ride) the calibration number jumped from the usual 430ish to about 530 (a lot more than, for example, the difference between indoor and outdoor temperature would make) and since then GC has been reading 30w higher again. The SRM still works accurately so it's a mystery to me and a bit disappointing.

So my workaround remains: use GC for the workout chart, include the target power on screen, remove the power output and use the Gamin for the power output instead.

@ Ale - That just hangs for me with the uinclip ..." message.

[Ale Martinez]

El miércoles, 10 de marzo de 2021 a la(s) 05:47:24 UTC-3, jamils...@gmail.com escribió:

@ Alan - I didn't fix this, but for a while I got a correct reading from my other power meter (I have two second hand SRMs, both about 10 years old - both work fine on the road and on Zwift. And if you have the patience, you can solder in new batteries yourself!).

For a month or two I was getting a very good reading on GC and Garmin on my other PM but one evening, when calibrating the SRM on the Garmin (which I do every ride) the calibration number jumped from the usual 430ish to about 530 (a lot more than, for example, the difference between indoor and outdoor temperature would make) and since then GC has been reading 30w higher again.

Looking at the code, default SRM Zero Offset calibration in GC is 400, without successful calibration the error will depend on how far the real zero offset is from that value.

 

The SRM still works accurately so it's a mystery to me and a bit disappointing.

So my workaround remains: use GC for the workout chart, include the target power on screen, remove the power output and use the Gamin for the power output instead.

@ Ale - That just hangs for me with the uinclip ..." message.

I don't have a SRM to try, may be other users can help you, but in the code there is a comment:

>note: can't calculate/display calibration torque if crank not turning, as time=0

while calibration starts when cadence goes to zero, so you could try to click the Calibration button while you are pedalling, then stop/unclick when the first notification to do so appears.

On successful calibration the following message should appear:

>Calibration completed successfully!

>Zero Offset xxx

>Slope xxx

[jamils...@gmail.com]

Interesting stuff, Ale.

So it was just a lucky calibration coincidence that meant GC was giving me a good readings for a while! The new reading of about 530 would certainly account for the increase that GC is now giving me.

I tried as you suggested but whatever I try, I can't get the calibration to work in GC - it just hangs, for minutes...

Is there a way to get into the code and adjust the calibration manually? The calibration doesn't usually move around much so I probably wouldn't have to do it very often.

[Ale Martinez]

El viernes, 12 de marzo de 2021 a la(s) 15:00:35 UTC-3, jamils...@gmail.com escribió:

Interesting stuff, Ale.

So it was just a lucky calibration coincidence that meant GC was giving me a good readings for a while! The new reading of about 530 would certainly account for the increase that GC is now giving me.

I tried as you suggested but whatever I try, I can't get the calibration to work in GC - it just hangs, for minutes...

Is there a way to get into the code and adjust the calibration manually? The calibration doesn't usually move around much so I probably wouldn't have to do it very often.

If you can build by yourself, yes: https://github.com/GoldenCheetah/GoldenCheetah/blob/d21a603fa155cf867f847a464b5662e58fd64163/src/ANT/ANTChannel.cpp#L58

OTOH, to remember the last calibration offset, like the recent fortius calibration does, would be a simple and useful addition, and it would allow to manually change the value in configglobal-trainmode.ini

[Ale Martinez]

I added a PR with this change: https://github.com/GoldenCheetah/GoldenCheetah/pull/3843, once the CI builds finish, the artifacts can be downloaded for testing as explained in https://groups.google.com/g/golden-cheetah-developers/c/5fZUO9DbJDY

[jamils...@gmail.com]

Thanks Ale.

I really don't understand how github works so from what you wrote, I guess I should wait for the next update of the program.

I tried adding this to my ini file but it didn't work, but I didn't expect it to!

[srm]

offset=551

[Ale Martinez]

El sábado, 13 de marzo de 2021 a la(s) 18:01:52 UTC-3, jamils...@gmail.com escribió:

Thanks Ale.

I really don't understand how github works so from what you wrote, I guess I should wait for the next update of the program.

I tried adding this to my ini file but it didn't work, but I didn't expect it to!

[srm]

offset=551

That's ok, but you need a new binary able to use that config.

If you are on Windows and want to give it a try, an installer can be downloaded from https://ci.appveyor.com/project/Joern-R/goldencheetah-knhd8/builds/38209054/artifacts, it is basically GC v3.6 DEV 2101 plus some enhancements like this one. 

[jamils...@gmail.com]

Thanks, Ale. It worked! Amazing.

I forgot to check if it remembers the value the next time you open the app but I guess it will. If it doesn't I'll add a note here.

For anyone with the same problem, this is what you need to do:

- Install V3.6

- Add these two lines to the "configglobal-trainmode.ini' file (in C/users/XXXX/Appdata/Local/GoldenCheetah)

[srm]

offset=xxx (the number that your Garmin reads for your SMR power meter)

Thanks again.