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Old 07-04-11, 03:11 PM   #1
wphamilton
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Jury-rig cadence meter

Can some gadget gurus check me on this? I hooked up an old cyclometer as a cadence meter by setting the wheel circumference to 1667 and display to kph, so I can read cadence as the speed times ten. The magic number came from a little scribbling, and if I'm right it's universal and spot on. If I'm not, hopefully someone will tell me.

I'm sure it's been done frequently, as simple and inexpensive as it is, but a quick search only turned up a thread where someone couldn't make his sensor work or something like that. Anyone know off the top of their head?
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Old 07-04-11, 03:17 PM   #2
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Cadence is your crank rpm. Wheel rpm is a function of crank rpm AND gear ratio. Your gear ratio is still variable, so you are not measuring cadence, unless you are riding a single speed bike.
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Old 07-04-11, 03:28 PM   #3
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I don't see the objection kenji. The cyclometer measures revolutions of the wheel and multiplies by a factor (depending on wheel circumference) to produce speed. Changing the factor appropriately should measure cadence.

If you meant that I have to change the setup from the wheel, I kind of assumed that was taken for granted. I put the sensor on the chain stay and stuck a magnet on the crank arm.
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Old 07-04-11, 03:33 PM   #4
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Ok, I get it now. I thought you were still trying to use your computer to measure your speed too. If you moved the sensor to measure the crank rpm, then that might work. I like to see both when I ride.
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Old 07-04-11, 03:42 PM   #5
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Quote:
Originally Posted by kenji666 View Post
Ok, I get it now. I thought you were still trying to use your computer to measure your speed too. If you moved the sensor to measure the crank rpm, then that might work. I like to see both when I ride.
That's why I did it. I can only read the big numbers comfortably and had an extra beat-up cyclometer, so now I have two displays (two cyclometers). One regular one showing speed and distance, the other showing cadence (I think). I'm wondering if anyone else who's done that can verify the setting I came up with. It seems right.
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Old 07-04-11, 04:21 PM   #6
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Just a "by the way" moment..........it's "jerry-rig". Jury rigging is a VERY serious crime!
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Old 07-04-11, 04:38 PM   #7
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I guess I'm more inclined to the nautical than old english, but either way an impartial verdict is all I ask

edit: I checked over my math last night and it is correct, so I'll close off the question and leave this for anyone who wants a cadence meter but doesn't want to buy one. An $8 walmart cyclometer works fine.

In summary the magic number is 1667 with the kmh setting. You'll probably have to splice the wire to lengthen it. Sensor on chainstay, magnet on crank arm arranged to just miss the sensor and it works like a charm!

Last edited by wphamilton; 07-05-11 at 07:05 AM. Reason: summarize
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