Power meters and the 935

Another thought here is where is your 935?

I have found that on my wrist I can get lots of drop outs to my power meter (the original Rotor)
However if I put it in my top tube bag then it seems fine so must be a range thing.
OK that is not ideal outdoors but indoors you can largely put it wherever you like.

Another thought here is where is your 935?

I have found that on my wrist I can get lots of drop outs to my power meter (the original Rotor)
However if I put it in my top tube bag then it seems fine so must be a range thing.
OK that is not ideal outdoors but indoors you can largely put it wherever you like.

Well it's a watch, so it's on my wrist. And this is just a road bike so not like aero position. And a medium size bike. The interesting thing ISN'T that there were dropouts (all though that is bad for a new watch especially when I don't have the same issue with an Epix). The interesting thing was the interval. It wasn't just some basic interference since scoetser75 was seeing a similar interval. I'd guess there has to be some logic/timing in the 935 causing it.

Sure you can put it where you want, and I want it on my wrist. At this point, we shouldn't have to work around technology limitations, especially for things like this that work on older devices. Saying I should move it sounds more like an excuse for Garmin than a real solution.

Agreed it "needs" to work on your wrist but if it doesn't it helps to know if the issue is a range one or not as working out the issue means you are on the way to a solution or at least a workaround.

Ok, so today I placed my watch right next to my Kickr. To minimize any possibility of ANT+ interference with the devices, I connected to my Kickr & Wahoo cadence over Bluetooth using the Zwift iOS app, and then the Kickr (power & speed), Garmin HRM-Run and Garmin cadence sensor connected to my 935 over ANT. Phone was placed 2 meters away. The 935 now is next to Kickr, closer to my cadence sensor, but slightly further away from my heart rate strap. The result...

I did a loop of Hilly Loop and then Flat Loop totaling 21.23km. I never stopped pedaling once and tried to maintain a stead cadence of 85 (I may have gotten a bit excited in the sprint, so higher cadence there :))



The result:
- There is still a very predictable drop in power (every 90-100 seconds)
- There is also drops in heart rate - from my Garmin strap
- There is also drops in speed - from the Kickr
- Cadence remained pretty solid, except for 2 drops at the end. Remember, my watch was almost underneath my crack!
- There is no predicable pattern for speed or heart rate. Except for the very first drop 1 minute in, speed and heart rate dropped at the very same time.

I believe this is not just a Kickr issue but rather a Garmin 935 sensor drop issue. Maybe the introduction of Bluetooth Smart & WiFi on the device has placed the ANT receiver in such a position that it is causing interference or just gets weak signals. But this does not explain the predictable pattern for power. Something is happening with the device (software or hardware) every 90-100 seconds. Maybe the device initiates a transmit over BlueTooth to phone at that interval? I disabled the phone previously and same happened, so not sure.

Anyway, I believe we will see a recall (if hardware) or an update to software to resolve this!



Cheers
Shane

935 very sensitive to interference

Ok, i have done some more testing today to try and figure out what is going on with the 935 sensor drops. I tried to eliminate all factors that could impact the readings. So today is did 3 rides of 10 min each at a constant cadence (as far as possible).

My Setup
- 820 = mounted on my handle bar close to my stem.
- 935 = on my wrist, but I tried to keep my hands on the bars as close to my step as possible and did not move my hand while riding (just to keep some consistency).
- Rollers = Standard rollers with Garmin speed, cadence and heart rate.
- Kickr = Kickr transmitting power & speed, with Garmin cadence & heart rate.

Ride 1 - rollers -
First ride was on rollers on my porch by the pool. You can see that my 820 had 3 drops in speed and cadence. The drops did not happen at same time. Heart rate was solid with no drops. I guess it is because heart rate was close to device that any interference was ignored or signal remained strong enough. The 935 had a lot more drops at not predicable pattern.

Ride 2 - rollers - WiFi off -
Ok, so then I decided to turn all electronic equipment off that may cause ANT interference (like phones, WiFi, etc.). My closest WiFi was a Netgear NightHawk range extender at about 10 meters. Remember that it is located inside the house (TV room) and I am outside the house by the pool. The readings is perfect. Not a single drop from my Garmin sensors and my 820 & 935 is a match. This is pretty amazing and I was really surprised at the result. Maybe a range extender (2.4 & 5 GHz) is just too strong and cases issues.

Ride 3 - Kickr - WiFi off -
So now I remained in the exact same position, but introduced the Kickr. It was power by an extension cord while all other electronics remained off. The 820 had almost perfect readings with only 1 drop from power 30s into the ride. It also had some minor power reductions at 2:22, 5:50 and 9:07 into the ride. But this coincides in a slight drop in speed also (I think I may have slowed my cadence which was already slow-ish). Then if you look at the 935, dropouts in speed & power. Remember that both come from the Kickr. The cadence and heart rate was solid from Garmin. The speed drops seemed to happen every 210 seconds while the power was far more frequent at 90-95 seconds. There is a very real pattern here!

Conclusion
1. WiFi has a big influence on ANT devices, so try and stay away if you want good results. What was amazing was just the big impact as I thought I was ok being outside and relatively far from the device. Might be an option to reduce transmit power if you can deal with shorter range.
2. The 935 is more sensitive to interference or weak signals than the 820. Not sure if the 935 has the same hardware as the 820, but think not due to the form factor changes. Also not sure if additional hardware in 935 (like Bluetooth Smart sensor support, optical heart rate) cases a weaker ANT signal?
3. There is still something wrong in how the 935 deals with a weak signal coming from Kickr. Either the 820 has a better ANT receiver allowing it to ignore interference, or better software? What is clear, with the exact conditions, the 935 is more prone to drops.

I do not have an actual bike power meter, the Kickr is my only power source. So to really eliminate if this is a Kickr or Garmin issue, I will need to simulate this using a real power meter. I am a Zwatt backer and still waiting for my power meter, so will have to wait to test when I get it. Except if someone wants to send me a power meter to test. :D

The question remains, is the Kickr sending out weak ANT signals or causing interference that disrupts the 935? I am still unable to connect my 935 to the Kickr over Bluetooth (also another test to see quality of signal) as that will remove potential 2.4 GHz interference.

I am keen to hear what you think?

Cheers
Shane

nice investigative work. There is definitely something going on with the 935, whether it's software or hardware, that seems to make it more prone than past devices. Let's hope it's software. Interesting with the wifi interference across the board. Also wonder if the Kickr exasperates the problem with it's BT / Ant+ signals.

Companies like Garmin and Wahoo must have some pretty good data on interference from various sources like wifi and cell phones. It'd be nice if they would share that data with us.

I have PowerTap P1

My question is HOW do you pair it together? I can't find anything anywhere on how to pair it. I have had a 910xt for 4 years and just yesterday I got my FR935 and am struggling to figure out how to use it.

The 90-100s dropout on the Kickr is a Kickr issue (it occurs with the 310XT and 920XT too) - DCRainmaker seemed to think it might be something to do with the communications chip being reset.
You can solve it by going back to (I think) the 1.3.32 firmware on the Kickr, though obviously you lose a lot of Kickr updates by doing so!

Please let Wahoo know if you're suffering from it as it's a pain in the backside and they keep telling me they're working on it.
https://support.wahoofitness.com/hc/en-us/requests/new