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IMU Notes

amcdonley

Posts: 159
Joined: 2015-Jan-27 Tue 1:56 am
Location: Florida, USA

AGREE? “IMU WORTHLESS FOR SIMPLE ROBOTS’ X, Y, HEADING?”

Postby amcdonley » 2019-Aug-01 Thu 1:29 am

Found a phenomenal [90 page introduction and analysis](https://arxiv.org/pdf/1704.06053.pdf) (university level, but first and last sentence of some paragraphs are understandable):

Manon Kok, Jeroen D. Hol and Thomas B. Sch ̈on (2017), ”Using Inertial Sensors for Position and Orientation Estimation”, Foundations and Trends in Signal Processing: Vol. 11: No. 1-2, pp 1-153. http://dx.doi.org/10.1561/2000000094

My conclusions from the paper:

1. IMU heading error quickly becomes 10-30 degrees
2. By itself, no IMU can give useful path and heading.

And my conclusions from this mental excursion:

1. Our body also suffers from the same rapid “eyes closed” error accumulation
2. Brooks is correct that environmental references are stronger than symbolic representations (world coordinates), for the robot mobility domain.
3. Vision will be the most powerful sensor my robot already has, among encoders, TOF distance, microphone, and camera
4. Robotics is (still) hard.

Last edited by amcdonley on 2019-Aug-01 Thu 4:33 am, edited 1 time in total.

blimpyway

Posts: 99
Joined: 2018-Mar-19 Mon 9:18 pm

RE: AGREE? “IMU WORTHLESS FOR SIMPLE ROBOTS”

Postby blimpyway » 2019-Aug-01 Thu 4:09 am

try to make a simple two wheel balancing bot (segway bot) without an imu.

amcdonley

Posts: 159
Joined: 2015-Jan-27 Tue 1:56 am
Location: Florida, USA

RE: AGREE? “IMU WORTHLESS FOR SIMPLE ROBOTS”

Postby amcdonley » 2019-Aug-01 Thu 4:32 am

blimpyway wrote: 

2019-Aug-01 Thu 4:09 am

try to make a simple two wheel balancing bot (segway bot) without an imu.

Understandably impossible for the “keeping its head up” function, but can it provide accurate (world frame: x, y, theta)? It’s a serious question. Am I wrong about that application of IMU?

MrMecatronico

Posts: 1
Joined: 2019-Aug-02 Fri 1:40 am

RE: AGREE? “IMU WORTHLESS FOR SIMPLE ROBOTS’ X, Y, HEADING?”

Postby MrMecatronico » 2019-Aug-02 Fri 2:17 am

blimpyway wrote:try to make a simple two wheel balancing bot (segway bot) without an imu.

Balancing a reverse pendulum and providing heading and absolute World position are two very different problems.

amcdonley wrote:
My conclusions from the paper:1. IMU heading error quickly becomes 10-30 degrees
2. By itself, no IMU can give useful path and heading.

And my conclusions from this mental excursion:

1. Our body also suffers from the same rapid “eyes closed” error accumulation
2. Brooks is correct that environmental references are stronger than symbolic representations (world coordinates), for the robot mobility domain.
3. Vision will be the most powerful sensor my robot already has, among encoders, TOF distance, microphone, and camera
4. Robotics is (still) hard.

Balancing the reverse pendulum is solved by feeding directly the accelerations measured by the IMU to the stabilization control system.

On the other hand for the path and heading problem, those variables you what to measure are second derivatives of the IMU original measured variable (linear and angular accelerations). This means you have to integrate twice the IMU measure in order to get an estimation of world position and heading.
Integrating sensor signals is tricky and risky, on each subsequent integration step you are not only adding a signal increment, but a bunch of random noise too. This means that depending on the sensor noise and for how long you’ve estimated the coordinates you’ll get an error on those coordinates.

Your conclusions from the paper are correct. In fact, for useful path and heading on mobile robotics statistical filters are used (e.g. the Kalman filter), mixing different sensor measurements (encoder odometry, GPS, vision estimations,etc..).

Hope i’ve helped :)

PS: robotics is still hard yeah, but challenges are fun ;)

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Gavinmc42

Posts: 3264
Joined: 2013-Aug-28 Wed 11:31 am

RE: AGREE? “IMU WORTHLESS FOR SIMPLE ROBOTS’ X, Y, HEADING?”

Unread postby Gavinmc42 » 2019-Aug-02 Fri 12:45 pm

The newer drones use Optical flow sensors for hovering.
Pixart have one that can be used with Crazyflie.Quaterions and Kalman filtering?
GPS helps to nudge them back on track, later RTK GPS for centimetre accuracy.

I have some hope Bluetooth 5.1 will help for indoor and short range bot.
Optical sensor from a mouse for movement/direction sensing.
Indoor Lidar is now single chip, scanning versions cost more.

Everything helps but the maths is hard ;)

I’m dancing on Rainbows.
Raspberries are not Apples or Oranges

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