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Polar 710 HRM(11 posts)

Polar 710 HRMvo2max
Jan 10, 2002 12:11 PM
Has anyone used the Polar 710 HRM with the Power option? Does the power option really work? I mean, sensing chain vibration seems a bit hokey to me. What if you're riding on a rough road? If they had an instrumented link you could add to your chain, maybe. Also, any problems downloading data and uploading workouts back to the watch? Thanks!
Interesting Idea...FooBar
Jan 10, 2002 1:24 PM
Haven't used one personally, but I would expect that the road would have to be somewhat bumpy for the power option to even work. Vibration frequency is related to something like the square root of tension (I think, at least in the standing wave on a string approx), the amplitude shouldn't matter as long as it isn't too large. However, over really choppy surfaces, I would expect the whole approximation to break down because of the large amplitude of oscillation. Once it has the tension and speed, the power should be pretty easy to calculate. The only thing I wonder is how it measures the properties of the chain... Or if that is fairly constant across manufacturers.
Turn it around....grzy
Jan 10, 2002 2:06 PM
Notice that the power option for the S710 isn't actually available. If it really worked one would think that it would be on the market - given how long the S710 in it's basic form was delayed. Call me skeptical, but I think there are some pretty big challenges in pulling off this new paradigm for power measurement on a bike. I'm certainly not going to be the first kid on the block with one. So far it's vaporware.
measuring powerDog
Jan 10, 2002 2:16 PM
I thought someone posted some charts showing the use of the power option. Did they sell them then pull them off the market?

I can't imagine the technology working, either. You could something possibly measure chain tension accurately enough to convert to power? I suppose a couple of very accurate lasers could measure chain stretch...

Any other ways to measure power? All of the existing ways measure at the hub or crank, right?

measuring powergrzy
Jan 10, 2002 2:27 PM
No, the charts posted earlier didn't actually have power on them - just HR, speed, altitude, distance and time. They have yet to release or even demonstrate the power option actually working on a bike. Power is work done over time and work is force over distance. For example one horsepower is raising 550 lbs. one foot in one second. So if you know the tension on the chain and how fast (velocity is distance over time) the chain is moving you should be able to get power - at least on paper. The only difference between power at the crank vs. the hub is the losses in the drive train in going from the crank to the hub. That one could get any of this stuff to work on a bicycle and not pay a huge weight penatly and be reasonably priced would be quite an accomplishment. I think that they ultimately will get it to work, but it's not going to be easy. At the very least there will have to be some selective electronic filtering of the raw signal from the chain to distinguish oscillation of the chain from tension vs. a road.
Jan 10, 2002 2:32 PM
Will any power measurement system necessarily have some drag (use some of the power), even disregarding the weight?

Jan 10, 2002 4:37 PM
Not necessarily. There are many ways to measure power and many do not involve or actually require appreciable power from the system trying to be measured. When most peole think about measuring power they think of things like dynomometers and what's called "brake horse power" where a load is put on the sytem to get the measurement. Obviously it might be nice to know what an person is capable of (ergometers are used in crew) but this isn't going to help you much in a race. For example one could measure the power of a cyclist by Knowing the weight of the rider and bike, the elevation gain and the time it took to climb it. Actually this would be the power measured where the tire hits the road, due to frictional losses and inefficiencyies the rider would have to supply more power and even then one would miss the power lost due to wind reistance (a function of velocity).

I think what you're getting at is if one were to have a system like the Polar S710 would there be a penalty paid by the rider in terms of lost power. I would say the answer should be no - after all who want's to ride around with the brakes on? Certainly the folks at Polar have to be keenly aware of this - no one is going to want to use their system very much if it saps any of the rider's power. One should realize that even if the sensor developed some sort of magnetic field in opposition to the chain movement it is virtualy at 90 degrees to the direction of motion/force of the chain and therefore would have no effect. Typically the voltages and amperages are extremely low and this is why a battery is required to amplify the (wireless) signal to transmit to the receiver.
Turn it around....mavic1010
Jan 10, 2002 3:40 PM
That's strange...saw a guy with the power option (710) on his bike this past weekend. Saw the chain tension meter thing I noticed was that his bike was cluttered with all that gadgetry on it...oh well to each his own...
Very Interestinggrzy
Jan 10, 2002 4:40 PM
Gotta be some one on the inside doing R&D for Polar. The product isn't released and you can't buy it from anyone to my knowledge. Even their website says "RSN" (real soon now), maybe it's not updated.
n/a at ExcelDog
Jan 10, 2002 4:51 PM
Excel usually gets things very eary, and they are not available yet, and no ETA.

two live sitingsphilippec
Jan 11, 2002 7:58 AM
I have seen two in use here in France. The set-up is cluttered and one rider told me the meter runs through batteries very quickly. He liked the pc transfer and charting, though.