Originally Posted by AriMB
It's not just after a collision though. Anything that would cause one wheel to slip and not the other would cause the same problem, even if the wheel isn't completely raised off the ground. This could happen in autonomous by driving over a small bump* or a slippery/sticky piece of field tape**, for example. If the wheel that's slipping is the one you're measuring, you may know that the wheel slipped (because the module turned unexpectedly), but you don't know how much distance you lost from slipping.
* flat fields often have unexpected 1/4" bumps (see 2017)
** FTAs do their best to keep all the tape lines intact and smooth, but you know as well as I that they get messed up by the end of a long competition
Understood. As I've said I'd likely do a 3 sensor approach at the minimum. But I think the Internally Indexed Differential Swerve would be less susceptible to the error being described.