Perfect calibration with a i-magic & Powermeter

Anything about Power (watts)

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Perfect calibration with a i-magic & Powermeter

Post by Tacx Video Production » Sat Dec 03, 2005 6:58 pm

Well I finally got the i-magic running with a Powertap (my out side trainingbike). I can say that between 160watts - 350watts I have a extremely close match between the Tacx & the Powertap when riding a RLV in Catalyst. My Laptop (with all my training software) is away again to be fixed so I will have to wait a week or so before I can post some files but for now you can take my word that its possible to get a accurate slope with the Tacx. The Calibration test would not work for me so it was set to 0.0 the slope I had to adjust to 95. 100psi & a super tough (for Belgium roads)Armadillo tire (Specialized?) 3turns from first contact.

I tested both the big ring & small & all gears & power was always within about 10watts (bloody close in my eyes).

So if you have a power meter & a i-magic I will like you to set the slope in the Fortius/Catayst software to 95 & tell me if you get closer to reality.

If your on a Fortius set to 115 - 120 for the moment.

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Post by JohnSS » Sat Dec 03, 2005 11:30 pm

Phil, when you say you set the slope to 95, do you mean you set the scale factor to 95? I thought that the slope went from -4 to 9 in the Catalyst.

Is there a reason that the Fortius spin-down calibration didn't work for you? It's pretty important that we know the 'true' value of the spin-down because we don't all have 100 psi, Armadillo tires and 3 turns of the roller knob.

For me I have the Contential Home Trainer tire (bright yellow) and I get a Fortius calibration value of +0.3 to +0.5 with just 1 1/4 turns of the knob.

Could you pop into Capricorn and/or Sipscape and do a couple miles to see if the VR watts are the same as the Fortius Catalyst watts? That would be really great.

Thanks again for everything,

J.

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Post by Tacx Video Production » Sun Dec 04, 2005 2:48 pm

When I say slope Im referring to accuracy at say 150watts & continued accuracy at 400watts . If I could make it accurate at 300watts & it was wrong at 200watts then the slope would not be accurate. For the moment the slope is very good in both the big ring & at fast & slow speeds.

Im going to do some more tests & see if I can find the reason for some odd looking RLV caf files I downloaded a few weeks back where power dropped & HR actually increased when the riders started a climb.

Tire pressure & friction can account for a fair amount of power loss on a trainer so I will try my best to get some good spin down data from 30kph.

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Post by JohnSS » Tue Dec 20, 2005 5:25 am

phil wrote:Tire pressure & friction can account for a fair amount of power loss on a trainer so I will try my best to get some good spin down data from 30kph.
Phil,

Is there any chance that you can do a 15 minute warm up then adjust the roller pressure to give you a zero calibration in the Foritus Menus, then check the power accuracy of the I-Magic trainer in the Catalyst, Green VR worlds, Fortius VR worlds, (and beyond all hope, the FitCentric NA1 VR worlds).

If it is too much work to try them all, I would prioritize the list as Green VR, Blue Catalyst, Fortius VR, then NA1 VR.

Thanks,

John.

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Post by Tacx Video Production » Mon Jan 09, 2006 11:22 am

Just found some data on this laptop from a earlier test. Its only 11minutes but it has very variable power (descent of the virtual Col du Peyresourde & the start of the Col de Azet). You can clearly see the power slope is extremely close to the powertap.

http://www.tacx-video.com/Downloads/ima ... t-PTap.png

http://www.tacx-video.com/Downloads/ima ... stTacx.png

Next time I train inside I will do a longer ride on a RLV or if not I will rake up the ride I did on the Alpine Classic. Im 100% happy with the new i-magic slope. I need to test different tires & roller settings to see if there is a repeatable way to get it calibrated with out actually owning a shed full of expensive power meters

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Post by Tacx Video Production » Tue Feb 28, 2006 5:52 pm

Another SRM - Fortius test ride from the first 1hr riding on the Lombardy RLV.

Image

http://www.tacx-video.com/Downloads/ima ... ortius.png full image

Image

http://www.tacx-video.com/Downloads/ima ... SRMPro.png full image

You can see by looking at the best average data for the different durations on the left pane that the power was as good as spot on. Obviously instant power will be higher at the crank & the Fortius will display a power thats been smoothed a bit with a short lag behind the effort.

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Post by sima22 » Tue Feb 28, 2006 11:33 pm

Phill,

please explain how to change slope to 95, you said that is not scale to be changed to 95 ? Where is that in Catalyst ?

Thanks,
Alex

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Post by Tacx Video Production » Wed Mar 01, 2006 10:29 am

sima22 wrote:Phill,

please explain how to change slope to 95, you said that is not scale to be changed to 95 ? Where is that in Catalyst ?

Thanks,
Alex
If your talking about the i-magic then I would leave it alone unless you feel strongly that your power is too high or too low. Ideal is to calibrate it with a powermeter like a powertap,Ergomo or SRM. To change this go to the settings options menu via the first main menu (where you choose what you want to do). You should see a calibration button. Click this & you can set the slope (I think between 90 - 120) & also do a spin down test to get a accurate tire friction number. Do this after a good 30minute warm up to avoid any drift in the power data.

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Post by wczek » Wed Mar 01, 2006 2:25 pm

I have a Fortius why the 15-30 minute warmup? What difference does having a calibration of -1.5 or 0 or 1.5 make in the power values?

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Post by i-magic racing fan » Wed Mar 01, 2006 2:51 pm

probably less than 1%. Perhaps phil has the answer.

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Post by lemmy999 » Wed Mar 01, 2006 3:50 pm

No matter how long I warm up, I always get a 1.0 to 2.0 drop in the calibration/spin down while riding for an hour. If I start at 0.0 I will end up with -1.5 or -2.0 at the end of the ride.

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Post by Rein » Wed Mar 01, 2006 5:15 pm

lemmy999 wrote:No matter how long I warm up, I always get a 1.0 to 2.0 drop in the calibration/spin down while riding for an hour. If I start at 0.0 I will end up with -1.5 or -2.0 at the end of the ride.
Same here... :?

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Post by Rein » Thu Mar 02, 2006 2:33 pm

To correct my last post: yesterday after climbing Alpe d'Huez I got a drop in the calibration-value of 3! :shock:

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Post by lemmy999 » Thu Mar 02, 2006 3:49 pm

I do not know what the calibration factor does, but I sure hope it doesn't do much.

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Post by Rein » Thu Mar 02, 2006 4:48 pm

I'm afraid it does: when I did Alpe d'Huez with calibration-value +4 it took me 2 minutes more... Power-values seem to be comparable though...

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Re: Perfect calibration with a i-magic & Powermeter

Post by paolotom » Wed Dec 06, 2006 5:55 pm

[quote="Phil"][color=blue]Well I finally got the i-magic running with a Powertap (my out side trainingbike). I can say that between 160watts - 350watts I have a extremely close match between the Tacx & the Powertap when riding a RLV in Catalyst. My Laptop (with all my training software) is away again to be fixed so I will have to wait a week or so before I can post some files but for now you can take my word that its possible to get a accurate slope with the Tacx. The Calibration test would not work for me so it was set to 0.0 the slope I had to adjust to 95. 100psi & a super tough (for Belgium roads)Armadillo tire (Specialized?) 3turns from first contact.

I tested both the big ring & small & all gears & power was always within about 10watts (bloody close in my eyes).

So if you have a power meter & a i-magic I will like you to set the slope in the Fortius/Catayst software to 95 & tell me if you get closer to reality.

If your on a Fortius set to 115 - 120 for the moment.[/color][/quote]

I have an Ergomo.
My setup is Tacx Basic + I-Magic upgrade
After a proper warmup (15'), 100psi pressure and 3 complete turn I found that I have to set to a value of 117 in order to have comparable reading in RLV and Catalyst
My 2 cents

Paolo

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Post by sima22 » Thu Dec 07, 2006 10:26 pm

Paolo,

I have the same setup as you, actually I have bought Tacx Flow first and then I-magic upgrade.

Just to clarify, when you said RLV & Catalyst are comparable to Ergomo , do you mean that both of them have same values as your power meter? I found that Catalyst training runs, on its own (not VR), are somehow harder (more real) to ride then RLV.

I also have to put slope to 110 and my tire pressure is 110psi, to feel harder, better and more outdoor-like resistance.

After this post I should maybe try to 117. What about calibration value ? Do you leave it at 0.0 value ? Also I have found that the best way to set "calibration" , at least for me , is:

1) Warmup of 10 minutes
2) Use Tacx Flow computer and try to calibrate to 0, if not , play with tire pressure and knob turns until 0 is reached. Record tire pressure.
3) Also do 40km/h test , to double check calibration

I do this only once, after that before each ride I just check tire pressure to be same as recorded.

Any comments ?

Ciao,
Alex

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Post by paolotom » Fri Dec 08, 2006 10:32 am

Alex,
with our setup RLV fells like outdoor riding (at least for me ...) between -1% and 6%; out of this range it seems to me unrealistic.
I have (or try to have) a 0 calibration value like you with roughly the same protocol.
With Catalyst we can set slope or watts values but their variation (manually) is obviously smoother than in RLV mode so we can get steady feelings.
In my experience I get more "outdoor like" values in Catalyst but on a RLV trip (for example complete Mallorca tour) my final results (avg and normalized watts) are not very different between Ergomo and Tacx.
Anyway there are too many variables that can affect 5/10% of the results (quality of tyres, inner pressure, number of turns after first contact of the wheel, temperature of the air, ...)

Paolo

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Rein
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Post by Rein » Fri Dec 08, 2006 11:00 am

I know it's a lot of money, but if you want realism, get a Fortius. Of course, it will never be exactly like on the road, but it gets pretty close, even up to +20%. But you will always have all those variables Paolotom is talking about influencing the results.
Unfortunatly it can be quite a hassle to get Fortius to work properly. Mine does now, and I wouldn't change it for anything else.
Just my 2 cents (whish that was the price of a Fortius :wink: ).

sima22
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Post by sima22 » Fri Dec 08, 2006 6:19 pm

Rein/Paolotom,

thanks for "exchange" of opinions.

Since I am in North America, different frequency of electricity here produced many "bad" Fortius stories (it is , after all , built for European voltage) so it would be a little "risk".

Also, I am planning to "upgrade" my Specialized Allez to new carbon-fiber bicycle, so I would rather spend money on outdoor feeling.

Thanks,
Alex

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