Sunday, September 22, 2013

ANT+ Trainer Power transmitter?

UPDATE: Didn't take long for the proof of concept video located on the post here
I was just reading DCrainmaker’s latest post on the a new silent trainer here, the Elite Turbo Muin. A lot of the feedback from people has been asking if the App does power why couldn’t they build in power transmission via a sensor!
Here is how I can do this, and I’ve thought about doing it.
  1. Get the regression curve
    1. Make it yourself with a real powermeter (Powertap, Quarq, SRM) with the LINEST feature in Excel for a 3rd or 4th order polynomial.
    2. Use the CSV file from the App and regress the curve yourself
  2. Using the reference code from Nordic Semiconductor in the SDK you setup a speed measurement with a reed switch / magnetic sensor and measure rotational speed.
    1. Two lines of code
      1. Calculate power based on speed
      2. Update ANT+ transmission
I can literally whip this together in a couple of evenings. If you think this is a good idea (for any trainer, not just this one) please write me at Maybe I would get my foot wet with Kickstarter for a multipurpose version first before doing a full blown powermeter.


  1. I believe that Peripedal software does this already - like many other real-time turbo programs it has a "virtual power" mode, but in this case it also broadcasts that virtual power via ANT+ so that a conventional head unit can pick it up.

    1. Correct, but in that case you'd need to buy the app (sometimes subscription based), and then also have the right OS as the app (which, aren't prevalent on mobile devices).

    2. I just want to do it as a standalone piece of hardware that can be updated with more trainers down the road so that people can use their existing cycle computers. Not everyone rides a trainer in front of a computer -- I mean I do, but not everyone.

  2. I am definitely interested for the Lemond Revolution and I think a lot of others would be to. The Power Pilot is expensive, bulky and only pairs via the Fitness Equipment profile so not any pure cycling devices.


  3. Hi Keith,
    That's what we do already at Kinomap: see the calculated power screenshot for example here:
    I'd love to share the curves that we already got : if you could implement something on your side to get more of these curves.
    We're doing the same with exercise bikes, based on Cadence for each level of resistance.
    Tell us.

  4. Hi Keith,
    It's a kind of chicken and egg thing... sort of.
    I've thought about doing what you have suggested as well but.........the thing is, if you don't have a power meter then you want to be doing what you are suggesting. Once you have a power meter to generate a curve you no longer need a curve. At least that's how it worked out for me anyway.
    Best regards,

    1. Welcome to your first time on my blog and thanks for the comment. This site has documented the development of three advanced powermeters. I own a quarq cinqo and have rental access to a power tap. I'm current building a crank based unit on the quarq to show the accuracy of my prototypes.

      I've also confirmed many months ago the regression curve used on the Kurt kinetic and outlined methods to make it much more accurate which is applicable to all trainer power sensors that are based on regressed curves.

      Not a chicken or an egg situation when I own both muscle chickens and multiple eggs.

    2. .........I meant, a person needs a direct force measuring power meter to generate the power curve relationship for a trainer that has speed measuring only. But once that person has a direct force measuring power meter they no longer have need to generate the power vs speed relationship curve.

  5. I would be interested. I have an old "Power" trainer that the software no longer "works" on. I don't need all the fancy head's up gizmo's that are sold with the latest high-end power trainers and would like to train with "power".

  6. Hi Keith,
    I think yours is a pretty cool idea.
    I don't own a powermeter. I own a TACX trainer which measures power so this is where I do my CP30 testing regulary.
    For Ironman I use a 650c triathlon bike (regular 130mm BCD) and for regular training I use a normal 700c roadbike (compact 110mm BCD). I haven't decided on buying a powermeter yet, since I don't know which one would be affordable and would fit on both bikes.

    Seeing how silent the new Elite Turbo Muin is and how much trouble I generate with my loud TACX trainer, I would love to get one. But since it doesn't offer a direct poweroutput per ANT+, I would really benefit from your idea.


    1. Hi Daniel,

      I can see your dilemma. Powertap is out as an option sadly.

      My Kurt is loud too. Sucks as an apartment dweller -- I always feel anxious about it and have always warned landlords. The Muin intrigues me too, but having the power measure on the result of speed sensor via an app is a poor choice. Some people have mixed views on if this is useful which I say depends on how you train.

      Anyway, my main project is Accuity which a lower cost L/R leg sensing powermeter. But I want to do some experiments with my Kurt Kinetic and see if I can get the math dialled in for acceleration measurement which will improve the accuracy. I have already started implementing a method of updating it so that it can be used generically with any trainer that there is a regression curve for.

  7. To speed switch transmitters, Woodward engine parts are reliable.

  8. This approach actually works pretty well. I created a simple inexpensive USB device where you can connect multiple bikes on different trainers to a computer. There are a few concerns like heat drift and quick accelerations. It will certainly not replace a power meter, but if you always use similar conditions and press on force with a coast down calibration, it is quite accurate. Here are the actual curves of trainers I have measured,