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Old 07-07-07, 08:23 PM
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TandemGeek
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Originally Posted by cdkassner
The proplem with attaching to the captain chainring or crank arm is that the distance to the frame is greater then the recommended 20mm.
You've got to think outside the box Dave....

Two alternatives exist here: move the sensor closer to the stock magnet or use a more powerful rare-earth magnet. I elected to go with the former for my HAC4's wired cadence pick-ups.

Since a picture is worth a thousand words, I've included 3k words worth of pictures below that illustrate:

1. A home-made cadence sensor mount I fabricated from scrap metal that screws into a pre-existing hole in my eccentric that I tapped for the 5m screw. The one in the photo is a spare off of our '98 Erickson: the joggle off-sets the sensor towards the frame, the two holes are for the small zip-ties that run through the sensor, and the cove simply follows the contour of the sensor. The single screw mount allows the mount to be pivoted independent of the eccentric's position... which is kinda important.

2. A side view of our '02 Erickson travel tandem's left-front crank to show where the sensor and mount are located in relationship to the eccentric and cranks.

3. A bottom view that shows the relationship of the sensor and the small magnet (that would be the square thing next to the sensor) that is JB Welded to the inside of my 34t timing ring just below the point where the chain plates come to rest on the ring's teeth.

These mounts have been in use for 4 years or so. I elected to make a mount because I don't like to zip-tie things to my frames, but it would be just as easy to make a small spacer out of hard foam, wood, or solid nylon that could be zip-tied around the boom tube just behind the eccentric shell. Again, a rare-earth magnet would also probably do the trick vs. the spacer but I'd be inclined to install it inboard of the chain on the chainrings so that the crankarm-mounted magnet didn't perturbate the chain.
Attached Images
File Type: jpg
sensormount.jpg (5.5 KB, 71 views)
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sensor2.jpg (25.9 KB, 129 views)
File Type: jpg
sensor1.jpg (20.0 KB, 258 views)

Last edited by TandemGeek; 07-07-07 at 08:38 PM.
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