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Old 12-14-2014, 07:26 PM   #1463 (permalink)
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Originally Posted by MPaulHolmes View Post
...I don't really understand what the reluctance flywheel thing is, but it would be awesome to get it working and be inexpensive...
Looking at the picture it looks like a Crank angle sensor.
The crank angle sensor is mounted close to the teeth on the cars normal flywheel. These are the teeth that the starter motor normally engages with to turn over the ICE engine. Also called the ring gear.
The sensor outputs alternating pulses of positive and negative voltage. A positive voltage as a tooth approaches the sensor, zero transition as the tooth is aligned with the sensor and then a negative pulse as the tooth leaves the sensor.
This gives an AC signal with a frequency the same as the frequency of the teeth passing the sensor.
So if you know the number of teeth on the ring gear you can work out the flywheels RPM and also the amount of angular change.
To get the absolute angle of the flywheel you would need to provide some sort of index. cts_casemod suggested welding two teeth together to get a longer gap between positive and negative pulses on those teeth. This may be difficult to detect or discriminate from a change in RPM especially at very low RPM.
Maybe a rare earth magnet added to a tooth would give a higher voltage pulse for that tooth and make it stand out from the crowd? So you would still get the same pulse interval as the other teeth so angle change and RPM detection wouldn't be affected and have a voltage threshold trigger for the index detection.
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MPaulHolmes (12-14-2014)