Which sensor is used to measure rotation or position of joints and wheels?

• A. Photocell
• B. Gyroscope
• C. Encoders
• D. Altimeter

Answer: (C)

Measuring rotation or position of joints and wheels is typically done with encoders. An encoder converts mechanical rotation into electrical signals that encode how far and how fast something has turned. There are two main types: incremental encoders, which output pulses as the shaft spins and require counting to know position, and absolute encoders, which provide a unique position value for each angle. In robotics, encoders are mounted on joints or wheels to track joint angles or wheel rotations for control and odometry. They often use optical or magnetic sensing and produce two signals in quadrature, letting you determine both amount of rotation and direction. The pulse count is then translated into a real angle or distance using the known resolution (pulses per revolution) and any gear ratios.

Light-based sensors like a photocell detect light levels, not rotation. A gyroscope measures angular velocity or orientation but not the actual absolute position without integration, and it can drift over time. An altimeter measures altitude, which is unrelated to joint or wheel rotation.