From 4ff60d5eb71e82d6cb398f08c62b508e5f08a860 Mon Sep 17 00:00:00 2001 From: Jet Hughes Date: Thu, 30 Mar 2023 09:00:52 +1300 Subject: [PATCH] vault backup: 2023-03-30 09:00:52 --- content/notes/10-orientation-sensors.md | 40 ++++++++++++++++++++++--- 1 file changed, 36 insertions(+), 4 deletions(-) diff --git a/content/notes/10-orientation-sensors.md b/content/notes/10-orientation-sensors.md index fbe105467..1ec1ad183 100644 --- a/content/notes/10-orientation-sensors.md +++ b/content/notes/10-orientation-sensors.md @@ -32,6 +32,7 @@ Accelerometers +![two phones|300](https://i.imgur.com/s45a4TF.png) Compass / Magnetometer - Measures the strength of earth’s magnetic field - Strength is expressed in tesla [T] @@ -41,11 +42,42 @@ Compass / Magnetometer ![Error around metal/magnetic objects](https://i.imgur.com/YIJAcGS.png) +Compass / Magnetometer +- Advantage: + - Absolute orientation measurement +- Disadvantage: + - Usually slow update + - Sensitive to errors + - Local discontinuities in magnetic field + - Ferromagnetic materials + - Power sources + +![gryroscope|300](https://i.imgur.com/VnL5seY.png) +Gyroscope +- Detects the current orientation of the device, or changes in the orientation +- Precisely: orientation can be computed from the angular rate that is detected by the gyroscope, expressed in rad/s [deg/s] on 3 axis. +- Traditional gyroscopes use the e!ect of angular momentum +![gyro deg of freedom|300](https://i.imgur.com/q1LjfPD.png) +![gyro electronic|300](https://i.imgur.com/5Ti80sO.png) + +- MEMS (microelectromechanical system) gyro +- Used in most smartphones or mobile/embedded devices +- Use the displacement of vibrating proof mass to compute orientation (Coriolis effect) +![MEMS gyro|100](https://i.imgur.com/dzTVCpE.png) +![gyro chip](https://i.imgur.com/zVoQ3wM.png) + +Problem: +- The gyroscope gives us angular rate with a unit of rad/s [deg/s] +- We can find the angular position at any given moment t with the following equation (assuming t=0 theta=0) +![eq1|100](https://i.imgur.com/CZKk1M7.png) +- We cannot take a perfectly continuous integral -> take the sum of a finite number of samples taken at a constant interval Ts +![eq2|100](https://i.imgur.com/vL0gRbV.png) +- Gyroscope data changes faster than the sampling frequency + - We will not detect it, and the integral approximation will be incorrect + - This error is called drift/bias as it increases in time, no return to 0o + + - - - - Recap - Several improvements to traditional GPS - AGPS for improved startup time and improved localisation using WIFI