The SMAC planner supports both the Reeds-Shepp & Dubin motion models for ackermann / legged robots.

The Dubin model can only move forward which RPP encapsulates perfectly. However Reeds-Shepp can allow the robot to reverse at a cusp (and point the opposite direction). So at these points we should move the carrot from the front of the robot to the reverse of the robot in those situations and invert the velocity so we can support reversing as well.

This figure shows a simple geometric view of the reverse cusping: https://github.com/leggedrobotics/se2_navigation/blob/master/pure_pursuit_core/doc/path_conventions.pdf

As well on the path smoother, do in sections