Intro to Inertial

Elecia White

Logical Elegance, Inc.

Embedded.fm

@logicalelegance

Plans

60%: Accelerometer, gyro, magnetometer

30% Navigation is hard 15% Kalman filters, quaternions are

awesome 10% Calibration is expensive 8% Summary of sensors,

applications, costs

You are here.

Intro to Inertial Sensors

Sensors

Accelerometers

Gyros

Magnetometers

Accelerometer

F V

X

Accelerometer

Sensors

Accelerometers measure gravity

Gyros

Magnetometers

Gyros

Gyros Angular Rate Sensors

Sensors

Accelerometers measure gravity

Gyros Angular rate sensors measure spinniness

Magnetometers

Magnetometer

Sensors

Accelerometers measure gravity

Gyros Angular rate sensors measure spinniness

Magnetometers measure north and magnets

Midpoint Quiz!

Stickers! Books! Win now!

Exclamation points are free!!

Axis

Axis

Look! Pretty lights!

Accelerometers measure gravity (apples)

Gyros Angular rate sensors measure spinniness (gestures)

Magnetometers measure north and magnets (compass)

Where am I?

Navigation is hard

Accelerometer

F V

X

F V

X

Accelerometer

Kidnapped and Blindfolded

Position Calculation

𝑋𝑎=𝑒𝑟𝑟𝑜𝑟𝑠𝑎+∫∫ 𝐴𝑑𝑡𝑋𝑔=𝑒𝑟𝑟𝑜𝑟𝑠𝑔+∫𝐺𝑑𝑡

Kalman Filter

"Basic concept of Kalman filtering" by Petteri Aimonen

Kalman Filter

I <heart> Quaternions

I <heart> Quaternions

http://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles

Calculate heading

https://github.com/adafruit/Adafruit_9DOF/blob/master/Adafruit_9DOF.cpp

Calculate heading: A+M

https://github.com/adafruit/Adafruit_9DOF/blob/master/Adafruit_9DOF.cpp

Navigation remains difficult.

Tactical Considerations

All sensors are temperature sensors, some measure other things as well.

Things to ask sensor vendors

Acronymic Combinations

A+G = Vertical gyro, A+M = Tilt compensated compass A+G+M = Attitude heading reference (AHRS) A+G+M+GPS = Fusion navigation solution

IMU, IMU with nav library 9DOF – accel + gyro + mag 10DOF – barometric and/or temperature

Barometric is for altitude but only good for relative measurements

Cost comparison

Prices change pretty rapidly Not recommendations, not exact

Sensor Specific Price Board

Price (1kq)

Accel MMA8451ADXL345

$8 (Adafruit)$18

$1.20$4.70

Gyro(Rate)

L3GD20HMAX21000

$13 $3.18$2.92

Mag HMC5883LMAG3110

$10$15

$1.55$0.78

IMU L3GD20H+LM303LSM9DS0 MPU-9150**

$20$20$35

$3.18 + 1.76 $5.32$7.12

Links and books

Embedded.fm episodes: 9 (Kidnapped and

Blindfolded) 43 (A Lot of High-Falutin’

Math) Adafruit 9DOF code (

github) Hackaday.io/elecia for

North Star IMU light example

Elecia White @logicalelegance

Thank you! Questions?