On 13/05/2019 16:56, Jeff Liebermann wrote:
On Sun, 12 May 2019 06:27:51 -0700, sms
wrote:

On 5/12/2019 1:29 AM, Tosspot wrote:
Anyone know of some 'decent' ones. The Sigma supplied ones won't
attract a whore in a crack house. The Bosch type ones always
seem to corrode and fall off, and on top of that are easy to
X-Thread. The Cat-Eye ones don't seem to stay put[1]. The
Echowell/Yamaha ones seem pretty decent but are like rocking
horse **** this side of the pond. Any other ideas?

[1] Yes, it is getting OCD!

When I lost the cadence magnet on my crank I used a hard-drive
magnet, i.e. https://www.ebay.com/itm/173209158372 but I got
some used ones from someone I knew at a disk drive company. I heat
shrinked it over the crank. I guess for a wheel magnet you could
use some cable ties or some baling wire and attach one of these to
the spokes. The pick-up doesn't have to be so close to the magnet
when you use a disk drive magnet.

I tried a disk drive magnet and had problems. The typical magnet is
not a single piece of iron with a single pair of poles, but rather
two magnets with two pairs of poles:
https://physics.stackexchange.com/questions/12283/if-you-place-a-spring-on-a-neodymium-hard-drive-magnet-it-appears-to-vibrate-in


By adjusting the position and orientation, it worked quite well.
However, if the magnet moved, I would get erratic operation. I got
my best resuls by breaking a magnet in half, resulting in (mostly)
one pair of poles. I don't recall which brand of bicycle computah I
used, but I think it may have been a Sigma.


Well, one old HDD reduced to component parts, we'll see how it goes over
the weekend.