UPDATE: WYBO Controller now offer an option to use the index. If your index signal is reliable, you will save time at each startup by activating this option.
What is encoder index ?
Encoder index is associated with a physical position of the encoder which activate the z-signal.
By using an index, you can theoretically memorize any position by simply tracking the number of turns from that index.
How does ODrive use index ?
When ODrive makes an offset calibration using index, it saves the number of turns of the offset position from the index position.
If you do not use index, you must do an offset calibration at every startup. That's what WYBO Controller do now.
Why WYBO does not use index ?
The problem with index signal is that it is subject to electrical magnetic interference (EMI). Just search "index" on ODrive forum and you will find a lot of issues linked with EMI and index.
For your index signal to be accurate, you need to have a very well shielded index cable. That is not the case for majority of builds.
Right now, we've chosen not to use it so we can keep our solution as reliable as possible. The only drawback is that the system must make an automatic offset calibration for all connected ODrive at every startup.
Nevertheless, we may add an option for index use in future versions.