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  1. #1
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    Laser spoke power meter for the wheel

    Project | Laser-spoke

    I'm surprised that not a lot of people talk more about this.
    I'm seriously considering joining their beta tester program and get my hand on one.

  2. #2
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    Ingenious idea. Will be interested to see if it pans out.
    A good habit is as hard to break as a bad one..

  3. #3
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    I'm curious how they will determine the rim/hub offset to torque relationship. It will be different for every wheel build.

  4. #4
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    Quote Originally Posted by ergott View Post
    I'm curious how they will determine the rim/hub offset to torque relationship. It will be different for every wheel build.
    I'm wondering this as well. If you apply the same power to two different wheels, you're doing to get different deflections.

  5. #5
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    Quote Originally Posted by tlg View Post
    I'm wondering this as well. If you apply the same power to two different wheels, you're doing to get different deflections.
    True, but it's just a calibration issue. At worst, the old trick of 1st gen powermeters, of hanging a known weight from the crankarm in a known gear would cover it. There's probably a more clever way to work it out.

    I'm going to guess this won't end up going anywhere commercially, but it's feasible.
    A good habit is as hard to break as a bad one..

  6. #6
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    I think the biggest issue they will have is variable friction if they let it be used on wheels with touching crossed spokes. Also, when you are cruising in a tall gear the torque on the wheel is pretty low. Will they be able to measure the tiny deflections accurately?

    I think their best bet would be to make a dedicated hub and wheel and calibrate it at the factory.

    At this point it looks like it's in the early concept phase. I'll be more interested when I see some viable hardware and test results.

  7. #7
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    Sounds like they are using 1 spoke for deflection measurment. Combine that with the cyclic/sinusoidal application of torque to the wheel, seems like self calibration would be near impossible.

    Someone is a laser fan, and this application is too much of a stretch.

  8. #8
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    They are measuring the rotational deflection between the hub and rim.

  9. #9
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    Quote Originally Posted by KevinK2 View Post
    Sounds like they are using 1 spoke for deflection measurment. Combine that with the cyclic/sinusoidal application of torque to the wheel, seems like self calibration would be near impossible.
    And if an owner could calibrate it to his/her wheel, what happens when the tension of that wheel varies slightly? This, I'll assume, could happen due to spokes stretching, bedding, loosening and temperature variations. Just wondering......
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  10. #10
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    Quote Originally Posted by rruff View Post
    They are measuring the rotational deflection between the hub and rim.
    Thanks for the correction. But I was thinking spoke location on rim, same thing as one point on the rim, based on his pic. All concerns still apply:

    "Sounds like they are using 1 spoke for deflection measurment. Combine that with the cyclic/sinusoidal application of torque to the wheel, seems like self calibration would be near impossible.

    Someone is a laser fan, and this application is too much of a stretch."

  11. #11
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    You can calibrate it by hanging a known weight from the crank... same as Powertap.

  12. #12
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    Quote Originally Posted by Mike T. View Post
    And if an owner could calibrate it to his/her wheel, what happens when the tension of that wheel varies slightly?
    Wheel stiffness is independent of tension so long as there is *some* tension.

  13. #13
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    Quote Originally Posted by rruff View Post
    You can calibrate it by hanging a known weight from the crank... same as Powertap.
    You could but this is what they claim: "Dynamic method of calibration integrated in our power meter is our most powerful secret weapon (patent pending). This allows real-time calibration by user on the go". But that's for the pro edition?

    I guess it's just the matter of reading instantaneous torque and rpm, and whether or not they can detect signal over the noise for lower torque levels. I have personally applied strain gauges on a wheel for other reasons, and have high confidence it this traditional way of measuring torque.

  14. #14
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    Would hard cornering also cause rim deflection?

  15. #15
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    Quote Originally Posted by rruff View Post
    Wheel stiffness is independent of tension so long as there is *some* tension.
    I guess I do remember reading something about that in Brandt and/or Rinard. It doesn't seem logical to me but they know more than I do.
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  16. #16
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    Quote Originally Posted by jnbrown View Post
    Would hard cornering also cause rim deflection?
    Not especially; to the extent that there is, it would be lateral, and wouldn't impact the measurements they'd be taking.
    A good habit is as hard to break as a bad one..

  17. #17
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    Quote Originally Posted by jnbrown View Post
    Would hard cornering also cause rim deflection?
    Lateral deflection. This device measures the rotational deflection between the hub and rim.

  18. #18
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    Quote Originally Posted by jnbrown View Post
    Would hard cornering also cause rim deflection?
    Not really, for the most part the force vector from your body's CG passes down to the tire contact patch. If you are leaning 20 deg from vertical, there is no lateral force on the wheel ... the horizontal force on the body times the height off the ground is balanced by the vertical weight vector times the lateral distance to the contact patch. I had to know this stuff when I designed the Specialized 3-spoke wheel.

    The highest lateral loads on the wheel occur during an out of saddle hill climb or sprint to the finish, where the bike is put through high angles, and stay in a vertical path.

  19. #19
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    Quote Originally Posted by KevinK2 View Post
    You could but this is what they claim: "Dynamic method of calibration integrated in our power meter is our most powerful secret weapon (patent pending). This allows real-time calibration by user on the go".
    Seems impossible to me.

    There are a lot of concepts for power measurement that initially seem promising, but turn out to have problems... simply because it is nearly impossible to accurately isolate the thing you are trying to measure to +-1 to 2% accuracy. Measuring the how much the rim moves rotationally vs the hub brings in all sorts of variables that say a Powertap hub doesn't have to contend with. Pedal based meters have a lot of inherent hurdles too. The Brim Bros cleat-based meters seem impossible to me... just too many odd forces to measure. Crank based meters are working well, but they also have more complicated issues to deal with than the Powertap. And then there is the iBike which could be fine in theory, but it is too difficult to accurately measure things like wind speed and tilt needed to determine power.

  20. #20
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    Quote Originally Posted by rruff View Post
    Wheel stiffness is independent of tension so long as there is *some* tension.
    I agree. You think of spokes in terms of springs, and the spring constant for a spoke is independent of the tension, as long as there is some tension to prevent the spoke from getting loose.

  21. #21
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    Quote Originally Posted by rruff View Post
    Lateral deflection. This device measures the rotational deflection between the hub and rim.
    Ok got it. I don't see why it wouldn't work then

  22. #22
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    Sure it will work. You can ride the bike and it will give you numbers. The numbers might even be within 10% or your actual power ...most of the time. Maybe not.

  23. #23
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    I am not sure why I need to know the numbers. I know when I am riding hard or easy.
    I ride because I enjoy it not attain some mythical watt number.
    Heck did Mercx or Hinualt know what their wattage was?

  24. #24
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    If you are looking to increase your pedaling efficiency, tools like this and others can be used. Mercx and Hinualt likely did not have these available back then, or could have had a Richard Virenque anti-tech mindset.

    Nothing wrong with your philosophy!

  25. #25
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    Quote Originally Posted by jnbrown View Post
    Heck did Mercx or Hinualt know what their wattage was?
    If they'd been invented, they would have used them. But if you aren't trying to squeeze as much power as possible out of your "engine", there is no reason to have a powermeter.

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