14 Choosing Sensors for Position, Velocity, and Acceleration
Position and Velocity Measurement
Measuring angular position is important in many mechanical applications and velocity and acceleration can be derived from measurements of position over time. Angular position can easily be used to track linear position through linkage mechanisms or spring recoil tapes or lines. (video 29:05) Slides are available as a PDF.
Inertial Measurement with Accelerometers and IMUs
GPS can provide position information, but it updates too slowly and measures too coarsely to provide immediate guidance for navigation of drones or autonomous vehicles. Inertial Measurement Units (IMU) have long been used to provide avionics guidance and more recently built into your phone to detect how far you walked and which way is up. (A test pilot colleague verified that a 2013 vintage iPad provides IMU data of quality very close to those in US Navy fighters.) The same chips that go in your expensive phone are available cheaply to build into your drone. IMUs are complicated by tracking rotation about three axes and translation along three axes with a lot of vector math, but the same ideas go into tracking linear motion along one axis.
Design Question: Can you adequately resolve short term position, velocity, and acceleration with an Arduino and an ADXL335 or LIS3DH accelerometer?
Accelerometers provide 3D measures of how quickly they are accelerating, plus the force of gravity. Rate gyros provide rates of rotation about three axes. Both are now available in MEMS packages to provide low cost inertial motion sensing in practical consumer products. Combined with magnetometers to act as a compass and GPS to provide a slowly updated position, sensor fusion can provide a detailed, time resolved picture of motion through space to support autonomous guidance of cars, drones, anything that moves. Slides for this video (13:12 pdf) provide a review aid.