This guide will show you how to clean your iRobot Roomba 4100’s optical encoder. The optical encoder is used to detect cliff edges and tell the robot to back up when nearing these. When the encoder is obstructed by debris it will cause the robot to continuously back up in a circle, aka the “circle dance“. Also, make sure to remove the battery before attempting to repair. Steps 1-3 cover removal of the battery pack.
If this guide does not fix your problem or a new problem emerges, check [[iRobot Roomba 4100 Troubleshooting]].