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Use an encoder wheel with a wider gap or cog in one spot. That's how most crankshaft sensors are designed. I don't think exact position is that critical for induction motors, only switched reluctance or synchronous AC. (In the case of switched reluctance, the motor itself can be used as a position sensor by measuring inductance.)
The ABS sensors (as well as camshaft and crankshaft sensors) I have seen are actually inductive. The sensor circuit applies a high frequency AC signal to the sensor and uses it as part of a voltage divider. The inductance varies depending on whether the sensing coil is over a cog or gap, which changes the impedance and the voltage division ratio.
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If America manages to eliminate obesity, we would save as much fuel as if every American were to stop driving for three days every year. To be slender like Tiffany Yep is to be a real hypermiler...
Allie Moore and I have a combined carbon footprint much smaller than that of one average American...
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