Scarab uses a velocity camera to estimate ground speed. This sensor is a downward looking camera that watches the ground move past. The camera is embedded in the belly, just behind the drill cavity and underneath the payload. An onboard computer performs optical flow calculations to convert sequences of images into estimates of motion.
The velocity camera sensor is part of a position estimation system. Other sensors measure vehicle acceleration and angular velocity. These measurements are updated many times every second and combined into a single estimate of vehicle position and orientation. The resulting data is called a pose estimate and is a fundamental building block used to create advanced vehicle behaviors.
The velocity camera is also used to estimate slip. By comparing ground speed with the velocity of each wheel, Scarab can determine whether the wheels have traction or are slipping. If the slip is significant, Scarab may reorient itself to prevent digging in the wheels.