bobthib

So I recently got a Garmin 910XT for training and tracking performance for my Tris. I also added a Stages Left Crank Power meter. The Stages unit installed easily and linked flawlessly with the Garmin. I did the simple Zero calibration. All seemed to be great!

But then the next day I did my first ride. In reviewing the ride, I noticed that the average power was about 45 watts and the unit was being picked up about 1/3 of the time.

I called Stages Cycling and they asked me about my set up. They made several suggestions and very diplomatically suggested that the Garmin 910XT would not reliably pick up a crank based power meter when worn on the wrist, but if installed on the base bar, it would work well.

Knowing what I know about antenna electronics and engineering, it makes sense to me that the antenna orientation in a device like the Garmin might be designed to provide the most sensitivity in one direction over another. These decisions are based on space and cost considerations, and require assumptions be made to guide these decisions. One decision would be the orientation of the device relative to the receiving device such as a power meter. Most power meters were hub based, and of fairly large size and stationary relative to the position of the receiving device.

The advent of crank or pedal based power measuring devices meant that although closer, the device would be smaller, and in constant motion relative to the head unit. So assuming that Garmin engineers made some basic design decisions to minimize size, power consumption, and cost considerations, and Stages engineers did the same, it is easy to see how the wireless performance could be "on the edge."

Anyway, I followed Stages advice and (1) set my recording to 1S(econd) vs Smart Recording, and (2) wear the Garmin on the outside of my left wrist. This did provide a substancial increase in recorded power and cadence, up to about 80% of the ride. There still was some pretty big gaps were I know I was pedaling (like who coasts for 20 senconds in the middle of a sprint?) but I think i got good data otherwise.

Next I'll try mounting the device on the base bar, per Stages, and see if that can fill in the other 20 %.

ANyone else have any experience like this?

anotherbrian

Blaming the other manufacturer when they don't have a reasonable explanation for why a problem is occurring seems easy enough to do.

I'd note that Garmin's wheel/crank transmitter is pretty small and they're probably trying to make it conserve as much power as possible (so have the transmitting power tuned down), and my Garmin Edge 500, 705, and 800's can all pick it up, as well as my Powertap's, from tens of feet away. I often forget my computer in the house until after I roll the bike out of the garage, and I'll go back inside, turn the computer on, and find it has detected the bike well before I'm close to it.

If you're training with power, having the display where you can see it (on the bars) during your workout without having to make any extra motions is probably best.

bobthib

I got the 910XT because it is a triathlon watch. In triathlon, following a strict plan regarding power output on the bike is critical to setting up the run. In addition, the transition time to go from swim to bike, and bike to run are critical times that don't allow for wasted seconds. I'm a competitive age grouper, and races are lost in transition. There is no time to worry about moving the device from wrist to bar and back again.

In addition, when the 910 was designed the power taps were in the rear hub, and hence stationary. I'm certain that fact was a critical assumption in the cost/benefit decisions to the final design.

The 910 should have been designed with an eye to having the watch on the wrist during the entire event, hence a directional antenna that would have sensitivity lobes that would maximize reception when the arm was in the aero position on the right wrist. IMHO

I'm left handed , and wear my gamin on the left wrist.

anotherbrian

Until you put your 910 on the bars and see that it works better than on your wrist, your conjecture about Garmin's design is pretty suspect. But even then, how do you know the Stage's isn't at fault and not transmitting at full power?

You would tend to think Garmin would design a watch aimed at the triathlete market to work with the ANT+ accessories triathletes use. In any case, my Forerunner 405 picks up my wheel/crank sensor just fine when I wear it on my left wrist.

As for powermeters, the electronics in my hub-based Powertap powermeter spin around the axle as they're connected to the hub shell, and Quarq (SRAM, ANT+ compatible) crank-based powermeters have been around since ~2010. Garmin should have had many years to perfect their compatibility with those, regardless if they're transmitting in a very focused beam away from your head unit, or (more likely) just blasting it out in every direction.

CharlyAlfaRomeo

Considering that the SRM crank based power meters were the industry leading product before the Cyclops stuff came along I think some of your assumptions are off base.

Could be that you have a faulty watch, could be a faulty PM. Might be they just don't play well together. Either way I'm sure you'll get it sorted out.

Have you considered getting a dedicated computer just for the bike? An Edge 500 is down around $200 shipped these days. Like you said precise metering during the bike leg of a triathlon is important so being able to easily see the information is paramount.

oespinoza83

I have had my Stages paired with an Edge 500 for almost 1.5 years now and never a problem. Not sure it matters, but Stages customer service > Garmin customer service, but both make really good products.

bobthib

UPDATE - 9-18-14 Based on the recommendation from Stages, I bought a "basebar" mount for the Garmin 910XT and a 90 degree mount for the areo bar. This way the 910 is strapped on to the 90 degree mount so it is facing me, and I can read it. The unit works PERFECTLY. I have done two rides with NO power dropouts ((910 set to ignore 0s in power)

I think this confirms my suspicion that the 910 antenna sensitivity pattern is a "dipole" (think of an elongated figure 8) extending out the top an bottom of the unit, like the strap. In this orientation, when you are wearing the unit on your wrist in the aerobar, the antenna pattern is pointing up and down.

When it is mounted in a horizontal position such that the face is pointing toward your face, the unit is tilted slightly, and the figure 8 (lower lobe) is pointing directly at the crank/rear hub area. It is very easy to see why design engineers, looking to minimize expense, power consumption, weight, size, etc. would likely assume that the unit would be mounted on a base bar. Unfortunately, triathletes looking to minimize T1 and T2 would prefer to keep the 910 on their wrist.

Now when we match this with a crank/pedal based power meter like stages, again we are dealing with design engineers dealing with the same constraints of economy of size, power, cost, etc, they are going to make assumptions and choices. Remember also that as opposed to a hub based PM, a crank/pedal based system is moving through the plane at a much wider angle. Granted, it is closer by about 18", and that is a BIG advantage, but coupled with an dipole antenna pattern, signal strength will be varying quite a bit. Now thing about making a right hand turn! Stages basic is a left crank system. Now you have moved the wrist mounted 910 another 6" away from the transmitter. It is easy to see why drop outs can happen.

In any event, just as design engineers make a lot of choices, we as consumers make choices too. And choices have consequences. I could have spent 2x as much and gotten a hub based PM, or a dual Stages crank set, or several other more expensive options. But MY criteria was too minimize cost. So I must live with the limitations that this choice brings. Since I have a satisfactory, albeit not optimal solution, I am very glad to report that I am happy with my Stages left crank arm Power Meter decision. I can recommend this to anyone looking for a low cost entry into training with power and willing to accept the limitations as discussed.

valygrl

You should check in with the guys over on slowtwitch - seems like that ability to wear it on your wrist through all the disciplines is the key feature of that product, there might be some discussion over there if this is really a known issue. And if it's not a known issue, maybe one of your devices is defective and you need a replacement, and then you can have the feature you want. If it was me, I wouldn't live with that.

elissonsayago

I also have 910xt and recently installed Stages Power Meter in my TT bike.
After reading Stages forum, I understood why my power meter drops all the time (I was paired with HR, but not forgot it at home).

I'd like to know if it's possible to use Stages Power meter in this configuration with 910xt ANT+ devices:

1) Stages Power Meter
2) HR Strap
3) Garmin Cadence sensor.

Will this work fine?

bobthib

Sorry for the delay in response, but in case you have not figured it out, it should work fine. This is how I run my TT bike and I have NO problems (probably 100 rides since this post) with the Gamin on the handle bar mount. I have it on a horizontal extention between the aerobars and the Gamin bar mount. It's a little tricky to mount and un-mount during transition, but don't try to rush it. Mounting is hampered by space limitations when I have the hydration unit fitted between the areobars. The key to quick un-mounting is to pull the strap end to disengage the "tongue" and then grab the tongue and pull that. Otherwise the tongue tents to get caught in another hole on the strap. A bit frustrating in transition, esp in short course!