[nuttle]

You have to pay attention to signal integrity when working with anything even slightly high-speed on the digital side car. We've had good success with SPI, but I don't want to take things off topic. Your project is great!

FWIW, here's a photo of a 6-encoder board we used for Lunacy, before it was legal to use CAN. This worked really well, it used the digital I/O lines as a bus to interface a similar (but non-SPI) encoder chip. At first, the digital I/O lines had enough bounce to cause occasional problems, one major source was the long round cable used to connect the cRIO to the DSC that year, at least if you went with the KoP solution. The ribbon cable connected to the digital I/O on the DSC and the other connectors were to encoders and coast/brake inputs (I think we decided this wasn't legal and left these off).

This type of thing is a good off-season project, it does normally take a while to get everything working well, including the software! Again, it is great that this is being done; thanks for sharing and good luck!