b'twin Cycle Computer Weirdness

[migrantwing]

I lost the spoke magnet that came with the b'twin cycle computer, so bought another, stronger magnet. It used to work with the previous magnet about 2mm from the fork sensor, which was always a pain. With this new, stronger magnet, the sensor picks it up from about 5-10mm away which is a lot more sensible. However...if I set up the sensor and magnet properly it rarely registers on the computer and, to get the two close enough to work, the sensor/magnet and spokes all knock into one another. Yet, if I flip the fork sensor upside down and back to front, it picks up really well.

Not that it's a problem aesthetically, I don't really care, but surely this can't be right? Pics below:

Pic 1: As the sensor should be set up (Park Tool screwdriver represents fork)

Pic 2: Not how the sensor should be set on the fork, yet it gives much better results and picks up from further away. The sensor is flipped upside down and back to front through 180 degrees in relation to the first picture.

 

[Racing roadkill]

I lost the spoke magnet that came with the b'twin cycle computer, so bought another, stronger magnet. It used to work with the previous magnet about 2mm from the fork sensor, which was always a pain. With this new, stronger magnet, the sensor picks it up from about 5-10mm away which is a lot more sensible. However...if I set up the sensor and magnet properly it rarely registers on the computer and, to get the two close enough to work, the sensor/magnet and spokes all knock into one another. Yet, if I flip the fork sensor upside down and back to front, it picks up really well.

Not that it's a problem aesthetically, I don't really care, but surely this can't be right? Pics below:

View attachment 102471

Pic 1: As the sensor should be set up (Park Tool screwdriver represents fork)

View attachment 102472

Pic 2: Not how the sensor should be set on the fork, yet it gives much better results and picks up from further away. The sensor is flipped upside down and back to front through 180 degrees in relation to the first picture.

The position of peak flux from the stronger magnet is further away from said magnet, than was the case with the weaker magnet, you've essentially moved the 'active' part of the sensor further away from the magnet by flipping it, it's now in the sweet spot of the magnetic field from the stronger magnet, where as when it was in the 'normal' position, it was in a weaker part of the Gaussian field intensity curve,which wasn't enough to fire the sensor up.

 

[migrantwing]

The position of peak flux from the stronger magnet is further away from said magnet, than was the case with the weaker magnet, you've essentially moved the 'active' part of the sensor further away from the magnet by flipping it, it's now in the sweet spot of the magnetic field from the stronger magnet, where as when it was in the 'normal' position, it was in a weaker part of the Gaussian field intensity curve,which wasn't enough to fire the sensor up.

That's either a brilliant reply...or complete horse sh*t! Hahaha!

I've tried two other magnets, which were similar (if not the same) as the original, older, weaker magnet, yet they both produce the same results as the 'stronger' magnet I mentioned. Could it be that the original magnet had a reverse polarity compared to the other magnets I've tried...or something? Why wouldn't they have used a stronger magnet in the first place, or moved the position of the sensor when manufacturing the sensor to achieve optimum results? To me, that's like putting a roof on the floor of a house as it keeps the rain out better?

 

[migrantwing]

From left to right:

New, stronger magnet that is on my spoke (Icarus from eBay), generic spoke magnet that I had lying around, and a magnet from a fridge magnet. All yielding the same results.

 

[Racing roadkill]

From left to right:

New, stronger magnet that is on my spoke (Icarus from eBay), generic spoke magnet that I had lying around, and a magnet from a fridge magnet. All yielding the same results.

They are a different shape and size. That's why, the flatter smaller magnet has a more diffuse mode field, therefore it could work with the sensor in either position, dependant on its relative strength.(the curve / hump is wider), the stronger magnet has a much sharper hump, with the area of best effect, being further away from the position of the weaker magnets curve / hump, and over a much smaller area, but with a much greater (greater than the sensor would ever need) intensity, so the sensor will only function in the 'odd' position, and with a much smaller 'window' of distance / position, in which it would function.

 

[migrantwing]

They are a different shape and size. That's why, the flatter smaller magnet has a more diffuse mode field, therefore it could work with the sensor in either position, dependant on its relative strength.(the curve / hump is wider), the stronger magnet has a much sharper hump, with the area of best effect, being further away from the position of the weaker magnets curve / hump, and over a much smaller area, but with a much greater (greater than the sensor would ever need) intensity, so the sensor will only function in the 'odd' position, and with a much smaller 'window' of distance / position, in which it would function.

Thank you, @Racing roadkill. Today, I have learned something very interesting