====== Michael Wrona notes ====== youtube name: MicWro Engr Note that these videos contain theory learned from Michael's reading. \\ He does not have any demonstrable hardware or software. ==== Intro to Inertial Measurement Units (IMU) ==== \https://youtu.be/LjeFZetmfYc?si=fNag0weh7Y1BTe6- Inertial Reference Frame \\ Earth-Centered Inertial Frame, ECI Frame \\ IMU = accelerometer + gyroscope + (optional) magnetometer ===gyroscope=== measures angular rotation rate in radians per second or degrees per second \\ has bias and drift \\ bias \\ when the sensor is stationary, the measurement is non-zero.\\ this means that the measurements are off-center. \\ drift \\ when we calculate the angles of the current orientation, by looking at the measurements over time, the bias in those measurements leads to drift in the current position angles. summary: gyro bias causes gyro drift how to eliminate bias and drift: Extended Kalman Filter === accelerometer === measures linear acceleration in 3 axes: x,y,z four accelerations: linear, gravity, coriolis, centripetal measured acceleration = linear and gravity - coriolis + centripetal coriolis and centripetal acceleration depend on earth's rotation, velocity, and position \\ These are fine measurements relevant only to high-precision sensors. by looking at acceleration due to gravity, we can estimate roll and pitch \\ roll, phi, φ \\ pitch, theta, θ integrate acceleration to velocity \\ integrate velocity to position \\ accelerometer also has bias which leads to drift in velocity and position \\ Extended Kalman Filter can be used to eliminate bias \\ accelerometer also has noise, due to vibration \\ Low-pass filter can be used to eliminate noise. Note: do NOT use a low-pass filter on gyroscope readings IMU grade and accuracy ^ IMU grade ^ acc bias ^ gyr bias ^ | unit | g | degr/hr | | Marine & space | 1E-5 | .001 | | Aviation | 3E-5 | .01 | | Tactical | .001 - .01 | 1-100 | | Automotive | >.01 | >100 |