special Hell-effect angle encoder
Quotespecial Hell-effect angle encoder"Hall Effect"
If you have access to the end of the shaft you can mount a magnet and use a special Hell-effect angle encoder.What you want is called an Absolute Shaft Encoder.
it senses speed.
Quoteit senses speed.No, it senses magnetic fields.You need a shaft encoder. I don't know of any solid-state ones, so a Gray code encoder is probably the only sensible absolute position sensor.
You have not said what kind of resolution you need. Austria Microsystems makes the Hall Effect absolute encoders in 8, 10, 12, an d 14 bit resolution (256, 1024, 4096, 16384 steps): http://www.ams.com/eng/Products/Magnetic-Encoders/Rotary-EncodersDigiKey has the AS5263 (12-bit) for $10.22 each: http://www.digikey.com/product-detail/en/AS5263-HQFT/AS5263-HQFTCT-ND/3028680
> Placing a gear around a steering shaft and using a stepping-motor driven worm gear, what would be a realistic resolution?If your stepper does 200 steps per revolution and your worm gear has 100 teeth that is 20,000 positions. Perhaps you would be happy with 4096 positions.> How do they connect to a shaft?Magnet on END of shaft. IC centered over magnet.> Can a hall-effect device be made to sense angular position without having rotation - so that when the device powers up, it knows what direction the single tire steering wheel is pointing?Yes. That's why they are called ABSOLUTE angular encoders. They tell you absolutely which way the shaft is pointing.
Yes. Either under or over. They show a cylindrical magnet but it is magnetized across a diameter, not from flat to flat as most cylindrical magnets.
Here is an example diagram:http://team358.org/files/programming/ControlSystem2009-/MagneticRotaryEncoderSetup2.jpgAnother example of use:http://www.electric-web.org/rotary_encoder.htmThis page has a picture of an evaluation board:http://www.digikey.com/product-detail/en/AS5048-DB-1.0/AS5048-DB-1.0-ND/3188614