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Ergo brain(8 posts)

Ergo brainmackgoo
Jan 21, 2002 12:41 AM
The directions mount the front wheel pick up 10cm from the axle. There really isn't any reason why I couldn't mount it higher up closer to the top of the fork leg is there?
I think that the idea there is to get the magnet as close to thebill
Jan 21, 2002 8:13 AM
hub as possible without being so close that the lower speed of the magnet's passing the sensor in the smaller radius revolution will compromise the accuracy of the instrument. Closer to the rim means more mass closer to the rim, making the rotating mass of the wheel greater, which is, theoretically at least, less desirable.
Not an issue in practice, though, is it?cory
Jan 21, 2002 3:58 PM
I agree that having the mass close to the center is theoretically better, but in practice, i wonder if you'd notice it. The computer's just a rev counter, and one end of the spoke goes around as many times as the other. If you like it up there for some reason (cleaner wire routing?), why not try it?
It's not about the weightKerry Irons
Jan 21, 2002 5:26 PM
The reason for placing the magnet closer to the hub is that it is moving slower when it passes the pickup, and therefore there is less chance of a missed "tick" as it flys by. There is a reasonable range for this, but some computers don't pick up the signal properly if the magnet is moving too fast as it passes the pickup.
Then why wouldn't Campy (or any other manu) tell youbill
Jan 21, 2002 7:08 PM
to put the magnet any distance from the hub? Just get it right down there on the sucker. But they all tell you not to (don't they?). Kerry, as much as you know about all this stuff, I'm not sure that you're right about the error coming from a magnet's moving too fast. I thought it's from the magnet's moving too slowly, too close to the hub.
oops. Should be, "Then why would Campy . . . nmbill
Jan 21, 2002 7:12 PM
nm
Well, maybeKerry Irons
Jan 22, 2002 4:34 PM
I can imagine the worry about the magnet moving too fast OR too slow. However, if slow movement was the issue, then the computer would likely break down (not work properly) at very slow speeds. I've never seen this as a problem. However, I have seen computers that miss counts when the magnet is moving too fast. So, I understand your point, but knowing how proximity switches work (they are either on or off) I doubt that there can be a problem from the magnet staying in contact with the pickup for too long.
...It's about the distance...Andy M-S
Jan 22, 2002 8:40 AM
Not having seen the pickup, I *suspect* the answer is distance. That is, much closer to the hub than 10cm and you're going to have a hard time getting the magnet past the sensor (or the fork, for that matter) without having the sensor hanging out in the breeze, because the magnet will be near the hub flange.

Much farther than 10cm, and it's hard to get the sensor close enough to the magnet as it goes by, because the magnet position is moving toward the centerline of the wheel, and away from the fork blades.

(With some computers, BTW, this is not a problem. I have my Planet Bike sensor mounted high to the inside of my right BRC blade, which makes it invisible and puts it in just the right relationship to the magnet--and also keeps the wire handling to a minimum.)

As I said, I haven't seen the 'Brain sensor (or magnet), so I'm just speculating, but I'd bet that mounting it much outside of the 10cm window is going to make for some contortions in getting the magnet to register properly without striking the sensor.