Quick question regarding the gear tooth sensor...

[Brad Voracek]

I've checked in the sensor manual, and understand how it works, I'm just not sure where exactly I should mount the chip, if it matters how close it is to the gear or what.
Also if any special type of gears are best? If someone could show me a few pictures and/or help me out a little with it, it would be greatly appreciated.

[Uberbots]

From what we have played with, we have detected a signal from about a half inch away from the gear. the best advice i can give you is to mount it as close as possible while still allowing some shake room.

[Phalanx]

From the datasheet on the sensor from the manufactures website:
http://www.allegromicro.com/datafile/0642.pdf See page 4.

Operational Air Gap Range AG DC within specification 0.5 – 2.75 mm

From the FRC 2007 Sensor Manual
A ferrous metal rotating gear (or sprocket, etc)

[Biff]

Last year we had good luck with keeping the sensors 2 to 4mm from our metal slotted encoders. As far as gears go I think you may have even more range. If you can hook an oscilloscope to the output it makes it very easy when things are too far away. As far as how many teeth, it depends on what you are trying to measure in the final analysis. There is a practical limit on how many pulses your program will handle. The closer to the motor when you are using reduction the more pulses you get. If you are using this in the drive train. Work backward from how accurate your tracking of the bots movement do you think you need. I.e. one inch or do you need better like 1/4". Then work the numbers back to the tooth counter.
Biff