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Re: Official power2max support thread [Dunbar] [ In reply to ]
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Hi Dunbar,

the rings on the FSA Gossamer cranks I have seen are usually not compatible, because they are non-standard. They have little cut outs around the chain ring bolt holes, which lead to warping when installed on another crankset, including our power meters. Whether your chain rings are indeed like this can really only be verified by inspecting them.

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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Question about Rotor 3D+ installation in a BB30 bottom bracket that I think was answered before, but I'm going to ask because the instructions just seem weird.

From the instructions here, it says two 1.6mm seals are needed. The crank didn't come with them, the bottom bracket (Wheels Mfg angular contact) didn't come with them. Are they talking about something like the outer seals that are used in PF30 bottom brackets?


It was answered in regards to OSBB before:

power2max wrote:
Hi TheForge,

the seal on the bearings is usually already installed on the OSBB bearings. On a BB30 bottom bracket you need to put the seal on the bearings. A simple way to check if everything is in order is when you have removed the existing cranks and have the bearings in front of you whether they are covered by a rubber or plastic seal or whether you have the bearings right in front of you.

The Rotor 3D+ doesn't come with bearings - you either get a BB30, PF30, BBRight or OSBB bottom bracket with it.

I contacted Rotor, and they said those extra seals are not necessary, so I'm just sitting here a bit lost as to what they actually mean. I installed the crank without them and everything seems to fit together fine, but I figured it's probably best to check.

Also, there wasn't actually any preload necessary, snugging up the drive side 8mm alloy bolt to torque spec seemed to take up any movement in the crank, normal?
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Re: Official power2max support thread [power2max] [ In reply to ]
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I may have actually asked this before, but perhaps policy is different now, and I don't remember so:

Suppose one buys a power2max power meter, and comes to believe that the units calibration is off, either due to comparison with other meters, or testing with a known weight, or other methods.

Is it possible to send the unit in to be checked/re-calibrated and what does that cost?

Also, while I am here, to what degree is the meter sensitive to swapping in different chainrings?

Suppose I swapped to a larger chainring for a particular TT, could that introduce error? Would things go back to normal once the regular chainring is back on, or is the unit sensitive to chainring bolt torque as well?



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Last edited by: jackmott: Dec 19, 14 13:32
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Re: Official power2max support thread [power2max] [ In reply to ]
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I've read about the calibration certificate and noticed I've never seen one. I went looking and eventually realised it's in the front cover of the manual, but all the fields are blank except for the printed signature.
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Re: Official power2max support thread [BeeSeeBee] [ In reply to ]
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Hi,

The seals and adjustment of play are specific to the bottom bracket. If you get a Rotor BB you get the bearing shields with it. I'm not sure about the spec of the wheels manufacturing bottom bracket.

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [jackmott] [ In reply to ]
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@jackmott: chain ring size doesn't affect calibration, you can change rings without adjustment.

Power2max power meters are designed to maintain a stable calibration for a long time. We can check calibration, but before sending in your power2max I would encourage a climbing test on a long and steep climb, which can check plausibility.

@fruity: the certificate can sometimes also be found on the box.

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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So I just received my power2max classic gossamer - The meter itself is brilliant! However the preload bolt (non-drive side) keeps falling out mid-ride, despite all bolts having been done to correct torque and installation instructions followed properly etc etc.

I've had a look on the internet and this seems to be a common issue - I was sort of hoping you'd be shipping the "newer" gossamers (The no-pinch-bolt design), but, more importantly, what is the solution to this problem for my crankset? I've seen loctite mentioned on the web, would you recommend this?

At the moment the product is not really fit for purpose given that I have to stop every hour or two to re-tighten the bolt - Is this really what all gossamer owners are expected to go through? I know the reviews online weren't great, but...

(P.s. The meter itself is great)
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Re: Official power2max support thread [iswmhamc891] [ In reply to ]
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Hi,

great to hear you like the power meter. The Megaexo model always comes in a pinch bolt design.

I haven't heard of lost reload bolts yet. To verify - you first tighten the preload bolt first and then the pinch bolts?

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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Yep that's correct. Then I'm seeing the preload bolt gradually loosen over the course of a ride. So far I've always managed to spot it and tighten it back up when it's started to come out.

The problem I'm having is also described elsewhere, e.g. here
Last edited by: iswmhamc891: Dec 20, 14 6:49
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Re: Official power2max support thread [iswmhamc891] [ In reply to ]
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Interesting, it's the first time I hear about it.

I'll ask my colleagues in Germany what they have heard about such cases and will come back to you.

Cheers
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [iswmhamc891] [ In reply to ]
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Yes i have seen it before on srm gossamers, i put a drop of low strength loctite on to stop it, also keep an eye out for cracks on the spline end of the spindle
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Re: Official power2max support thread [power2max] [ In reply to ]
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I'm just now seeing your reply. Thanks for getting back to me. I'll contact the european support.
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Re: Official power2max support thread [power2max] [ In reply to ]
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My 910xt doesn't seem to be picking up the signal from the meter. I'm probably just doing something wrong but does anyone know what could be the issue?

Also, will I have to take the battery out and put it back in? On the type s the crank has to come off in order to remove the battery on the Felt IA
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Re: Official power2max support thread [smoore89] [ In reply to ]
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Hi,

A few questions:
- Have you paired them before and did you get data before?
- When you spin the cranks on the Type S (after it hasn't been used or moved for a while), does the LED flash green?
- Is the 910xt in bike mode with power activated?

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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power2max wrote:
@jackmott: chain ring size doesn't affect calibration, you can change rings without adjustment.

Power2max power meters are designed to maintain a stable calibration for a long time. We can check calibration, but before sending in your power2max I would encourage a climbing test on a long and steep climb, which can check plausibility.

@fruity: the certificate can sometimes also be found on the box.

Best
Nicolas

Instead of a long hill climb, wouldn't it be more accurate and practical to hang a known verified weight from the crank arm or chainring and then measure the power meter response (static torque test)? I live in Houston where there are literally no long inclines or climbs. How does power2max calibrate their units before they ship to the customer?

Also - does power2max eventually plan to allow users to change the slope on their devices?
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Re: Official power2max support thread [power2max] [ In reply to ]
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Hey Nicolas,

Within bike mode I had to turn on a separate setting for power meters and it worked.
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Re: Official power2max support thread [aaronechang] [ In reply to ]
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@smoore89: good to hear!

@aaronechang: the reason we advise against a static torque test is that it's systematically biased, but the amount of the bias is variable. This makes the test results unreliable and not good enough to test factory calibration. Here is why: the higher the friction at the bottom bracket, the lower the proportion of torque transmitted from the crank arm through the power meter onto the chain. If, for argument's sake, your bottom bracket had seized and you couldn't move the cranks, then no torque would be transmitted at all and the power meter wouldn't register anything.

When you hang a weight off the crank arm bottom bracket friction is higher than during use, for two reasons: firstly the axle bends and cants the bearing inner race versus the outer race. Secondly a ball bearing that is not rotating experiences higher friction than a moving one - see "breakaway torque" documentation by SKF and other bearing manufacturers.

The result is that if you use a static torque test, the result will be biased. The magnitude of the bias depends on many factors and can't be generalized. That's why we advise against it - it's just not a good test.

Our calibration setup has been designed to eliminate this issue. We calibrate all power meters against a certified (by the German institute for calibration) true torque sensor precise to 0.1%. We also have some very advanced equipment that let's us test the precision and trueness of our meters during use, but that's our little secret how we do it :-).

I hope this clarifies,

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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A bike shop did my installation so I didn't get to see this part. Where is the LED?
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Re: Official power2max support thread [GAUG3] [ In reply to ]
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Hi,

Which model are we taking about? Classic or type s?

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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Classic.
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Re: Official power2max support thread [GAUG3] [ In reply to ]
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The LED is inside the battery compartment, unlike on the Type S. So you won't see it flash when the cranks wake up.

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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I understand your point of systematic problems in static calibration but still I have to ask why is there no option for user calibration? This cannot be technically difficult and considering that SRM has it and is considered the "gold standard" of accuracy it cannot be very harmful for the product imago either.

It would just be so handy when a user has multiple powermeters. As an example I have Quarq, Powertap and P2M. P2M shows about 5% higher than PT and Quarq shows about 2% higher than PT. Taking into account crank vs hub measurement and manufacturer tolerances they are all probably well calibrated and working good but that difference is just really, really annoying and I cannot think how convenient it would be to be able to adjust P2M to better match the two (regardless of which is actually "right").
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Re: Official power2max support thread [Frost] [ In reply to ]
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Hi Frost,

we have chosen not to make it adjustable because in our view this is no longer appropriate. You should be able to purchase a power meter that is true and precise and remains so.

Let me compare to cars: 30 years ago you could fiddle with the carburetor of your car. Nowadays you can't access the electronic fuel injection of your engine because there is no need to - it works as it should without fiddling and adjustment.

It will take a while for the mindset to shift and expectations to change.

Best
Nicolas

---
power2max
http://www.power2max.com/northamerica
official power meter of Movistar Team
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Re: Official power2max support thread [power2max] [ In reply to ]
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Hello and thanks for the answer. How would you then resolve the situation in my example above? If the answer is to switch all to P2M (just a hypotethical I don't think you'd actually propose that) what if then one P2M is -1.5% and another is +1.5%? That may sound nitty picking but if you've used a powermeter for a long time you'll actually notice that sort of difference.
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Re: Official power2max support thread [power2max] [ In reply to ]
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power2max wrote:
Hi Frost,

we have chosen not to make it adjustable because in our view this is no longer appropriate. You should be able to purchase a power meter that is true and precise and remains so.

Let me compare to cars: 30 years ago you could fiddle with the carburetor of your car. Nowadays you can't access the electronic fuel injection of your engine because there is no need to - it works as it should without fiddling and adjustment.

It will take a while for the mindset to shift and expectations to change.

Best
Nicolas

To complete the analogy - modern OBD (on-board-diagnostics) systems will automatically alert you (via a check engine light) if EFI is malfunctioning or there is a cylinder misfire or some other malfunction that needs attention. You can also plug in a scanner tool into your car's OBDII port and it will run a diagnostic check and display any error codes that were thrown by your car. This is standard across all modern cars produced within the past few decades and anyone can do it. There's no mechanical expertise needed - you literally just plug the scanner it into the port, push a few buttons and that's it. Where I live, you can go to your local Auto Zone or O'Reilly (auto parts shop) and ask to use their scanner. Or you can buy your own.

If your check engine light is not on and a scan tool indicates no error codes, that means your car is operating normally within the acceptable range of error defined by whoever came up with the OBD standard. If your check engine light is on, you can still probably drive your car (one of my previous cars was missing some key emissions control equipment so the check engine light was always on). But it's good to have a standard way to tell if any car is "out of spec".

For power meters - the standard method that everyone has always used is a static torque test. You can take a known, verified weight (I use a 20kg NIST-certified weight purchased for about $130 from McMasters-Carr, plus a 114g metal hanging tool that allows me to easily hang it on the crank spindle) and calculate the expected torque given: the total force that you're applying (in my case - 20kg + 114g), the force of gravity (in everyone's case - approx. 9.8 m/s^2), and the crank length. Apply this force to the power meter (by hanging the weight from the crank arm or the chainrings). Then measure the difference between the actual torque applied and the torque reported by the power meter and determine the % error. Very simple, and this is a method you can use for any power meter to ensure that all of your devices are within specification.

Regarding your note about BB resistance affecting the results of a static torque test:

Bottom brackets do provide some resistance, but the resistance is so small that it doesn't affect the validity of the test. This same topic came up in March or April on the Google Wattage forum (https://groups.google.com/...aI7Yp1o/otyfC_KmB9cJ). Someone did a test and found that, with the chain detached, a 10g weight applied to the pedals was sufficient to overcome any resistance from the bottom bracket and move the crank arm forward. With a 20kg weight, this is very insignificant (0.05% of the total weight used in the test). 0.05% might even be within the +/- range of error for an NIST-certified weight. So unless your bottom bracket is completely seized or has some other serious problems that prevent the crank from turning, BB resistance just isn't a significant factor in the static torque test.

In the dynamic situation (moving drivetrain), Friction Facts has found that the bottom bracket uses up about 0.4 to 0.6% of the total input force. Again - not a significant factor. There is a recent ST thread ("Best Bottom Bracket Ever") which touches upon this. In other words - the best bottom bracket ever will only net you about 0.5% extra watts.

In any case, if you were hypothetically building a power meter that promised accuracy to 0.01% and wanted to eliminate bottom bracket resistance - you could rig up a static torque test to bypass the bottom bracket / crank arm and hang the weight directly from the chain. Below is a photo of SRM's calibration rig in their Colorado Springs facility. In the same thread on Google Wattage (linked above), someone did just this (hung the weight directly from the chain) and received identical results compared to hanging weight from the crank arm.

Please understand that I'm not trying to unnecessarily bust your chops, Nicolas. All of us do appreciate you responding directly to our concerns and requests in a prompt manner. This is very refreshing and is above-and-beyond what other competitors provide.

But I did want to just state the case for why static torque analysis (or rather - any standard, repeatable testing procedure) should be used to verify claims of accuracy for any power meter. In the past, users who have done static torque analysis on even SRM units have found that their factory calibration is out-of-spec.

Trying to recall the phrase that RChung and Tom A. use all the time - "trust but verify"? If you can accurately verify, then you don't even need to trust. Well - other than trusting that your certified weight actually weighs what it's supposed to weigh.

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