A two-axis gimbal is a robotic mechanism that keeps a camera or sensor pointed steadily even when its base tilts or shakes. It usually controls pitch, which is up and down rotation, and roll, which is side to side rotation. This matters in drones, robots, vehicles, and handheld devices because clear images and accurate sensor readings depend on stable orientation.
By separating the motion of the base from the motion of the payload, the gimbal reduces blur and pointing error.
Key Facts
- Pitch rotation tilts the camera up or down about a horizontal axis.
- Roll rotation tilts the camera left or right about the viewing direction.
- Torque from a motor is related to angular acceleration by tau = I alpha.
- Angular error can be estimated as theta_error = theta_target - theta_measured.
- A basic proportional control command is tau = Kp theta_error.
- IMU sensors measure angular velocity and acceleration to estimate the gimbal orientation.
Vocabulary
- Gimbal
- A gimbal is a pivoting support that allows a payload to rotate about one or more axes while staying controlled.
- Pitch
- Pitch is rotation that points the camera or sensor upward or downward.
- Roll
- Roll is rotation that tilts the camera or sensor clockwise or counterclockwise around its forward direction.
- IMU
- An inertial measurement unit is a sensor package that measures acceleration and angular velocity to help estimate orientation.
- Feedback control
- Feedback control uses measured error to adjust motor output and move a system toward a desired state.
Common Mistakes to Avoid
- Confusing pitch and roll: pitch changes where the camera points vertically, while roll changes how level the horizon appears.
- Assuming the gimbal cancels all motion: a two-axis gimbal cannot directly correct yaw rotation unless a third axis is added.
- Ignoring the payload mass and inertia: heavier or more spread-out cameras need more motor torque because tau = I alpha.
- Setting feedback gain too high: excessive gain can make the gimbal overshoot, vibrate, or become unstable instead of holding steady.
Practice Questions
- 1 A gimbal motor applies a torque of 0.060 N m to a camera assembly with rotational inertia 0.020 kg m^2 about the pitch axis. What angular acceleration does it produce?
- 2 The roll angle measured by the IMU is 8 degrees, and the desired roll angle is 0 degrees. If a proportional controller uses Kp = 0.015 N m per degree, what corrective torque command is produced?
- 3 A robot base suddenly tilts to the right while the gimbal camera remains level. Explain how the IMU measurement and roll motor work together to reduce the disturbance.