Bicycle Mechanics - Cadence sensors - I've got an idea.

I've never liked having a cadence magnet on my crank arm because a zip strap half-way down the crank arm looks out of place there.

So, I've been thinking that some pedals (my Time's for example) have a 6mm socket on the inside of the spindle so you can install the pedal with a hex wrench instead of a open box wrench. What if I was to thread that "socket hole" so that a short cap screw fit in there with a strong (read neodynium) magnet glued into the socket on the capscrew. I guess you could also just glue a magnet right in the pedal socket too, but it might be too far away from a sensor mounted on the chain stay.

Has anyone tried this?

Campy tried it and it worked. That's how the cadence magnet for their Ergo Brain computer is installed.

Can you thread a hex shaped hole? if not, you could drill it out and mount a helicoil in there, as long as you've got wrench flats on the pedal you would still be ok. I think it's a neat idea however

Steve W

I stick my magnet to the pedal shaft directly(magnetically),
doesn't fall off even though it covers the hex hole.
I did not use the regular magnets though
I used the magnet from the inside of a computer hard drive, they are flat just like the bike magnets and used a nipper pliers to cut a piece that would fit over the pedal shaft.
These magnets are a little stronger so it holds good and has never fell off, but I think the regular magnets will also hold well or could be stuck with some silicone after cleaning the shaft.

Lennard

What about a little velcro?

are crankarms solid metal going back? If so seems that you could drill and tap a hole to take a 5 or 6 mm bolt and use that to mount the magnet on. That way you could adjust how far out it extended, and it wouldn't be noticeable at all.

smw

Can you thread a hex shaped hole?

Yes, if you are careful to get things lined up straight. I have threaded (6 mm) the recessed pivot bolt on my rear Ultegra brake and I mount the strut on my Tubus Fly Rack there (The bottom mounts on the QR). This gives me a small, very light-weight but strong (rated at 40 lbs.) and sturdy rack to carry rain gear, etc on long rides and because everything is mounted in my wind shadow there is little extra windage.

I have an even better idea, use a optical sensor! LED w/pickup that reflects off the crank each time it comes around. No need to mount a magnet...

An update: Last night I cut off the zip straps holding the Cateye magnet on my crank and substituted a 1/2" strong rare-earth magnet which fit perfectly inside the threaded pedal mounting hole on my Ultegra crank. It fits so well it looks like it came from Japan that way, no glue, no threading, nothing extra. I moved the sensor on the chain stay a couple of inches and it works perfectly. In fact I don't think I could ever get the magnet out it's in so tight, without taking the pedal off.

I used one of these magnets, which we use on our fridge: http://www.leevalley.com/wood/page.aspx?c=2&p=32065&cat=1,42363,42348&ap=1

can you post a picture of what this looks like? I am still slightly confused, though it sounds like a great idea!