Selecting an IMU

[Leolotowycz]

Finishing up an install of a auto pilot. Looking for advice on selecting a IMU that is friendly with PI 4.
Thanks In Advance for your thoughts/advise
Leo

[Adelie]

What’s an IMU?

[Reefmagnet]

Inertial Measurement Unit??

[banjoship]

https://forum.openmarine.net/showthread.php?tid=3120

[BillKny]

I'd normally expect someone who can only talk in acronyms to be smart enough to not have to ask such a basic question, unless all the acronym speak is just showing off...

[cal40john]

We use these in FIRST robotics. I've also been working on a drone that I'm programming with an Arduino so should work about the same on PI. Adafruit sells them on a breakout board with an I2C interface. The IMU has an onboard ARM that has a fusion output using filters (Kalman I believe) to make a stable output.


https://learn.adafruit.com/bno055-ab...aglebone-black

https://learn.adafruit.com/adafruit-...ntation-sensor

[Leolotowycz]

IMU. keeps a boat going from one waypoint to another.

[Leolotowycz]

Cf is a friendly site. In some way feel you have lost your compass. Your comment not helpful. Get in touch with your personal IMU.
LEO

[Leolotowycz]

Feel you lost your compass. CF IS A FRIENDLY SITE.

[Frankly]

A inertial measurement unit typically refers to a sophisticated /expensive unit that along with dead reckoning navigation determines the vehicle heading by measuring the rotational motion of the earth. Most of us poorer marine autopilot users still rely on good old magnetics to determine the vehicle heading. Newer units use accelerometers to correct the mag heading for vehicle motion and rate sensors to make for better autopilot performance.


Frankly

[Leolotowycz]

I like your response to explaining IMU. originally I looked at it in terms of mass and forces pushing against the mass, like current, waves, wind,, and the size of one's vessel.etc.
Thanks
LEO

[Bill O]

Originally Posted by Leolotowycz

Finishing up an install of a auto pilot. Looking for advice on selecting a IMU that is friendly with PI 4.
Thanks In Advance for your thoughts/advise
Leo

Leo,
What AP did you install? The pypilot "computer" has a 9 axis imu chip installed w/it already.

We used a different imu discussed here than what Sean has in his pre-made ap computer and works well (his imu choice may work better for his setup). I believe our imu has a new version, but depending on your setup could work for you.
Since the previous article, we have upgraded to a pi4 to integrate our new halo radar and everything seems to be playing well w/each other.

[Bill O]

Originally Posted by Frankly

A inertial measurement unit typically refers to a sophisticated /expensive unit that along with dead reckoning navigation determines the vehicle heading by measuring the rotational motion of the earth. Most of us poorer marine autopilot users still rely on good old magnetics to determine the vehicle heading. Newer units use accelerometers to correct the mag heading for vehicle motion and rate sensors to make for better autopilot performance.


Frankly

In actuality an imu is a "cheap" chip that does make an ap work better. If feel you are stuck w/an "old" technology ap, it is possible to upgrade w/pypilot w/o braking the bank.
The "old" tech ap works well if all you want/need is a point and shoot ap, but w/opencpn and pypilot it is a very inexpensive upgrade to get the latest and greatest.

It's an amazing difference.

[Frankly]

The point I was attempting to clarify was that an IMU determines vehicle heading by measurement of the rotation of the earth, most of our small craft autopilots use the earth's magnetic field to determine the vehicle heading. Since WW 2 this was typically measured with a fluxgate (gimballed to measure the horizontal component like your compass). New technology now uses a 3 axis magnetic sensor and resolves the horizontal component using a triad of accelerometers measuring the gravity vector. AHRS (attitude heading reference system) might be a more accurate description of the latter.

My current AP is a Raymarine Evo driving a 30+ YO Benmar chain and sprocket actuator. I spent a 30 year career designing automatic control systems for the US Navy, the novelty of which has long worn thin for me, but it is a fascinating technology, so have at it if that is your thing.


Frankly

[Northbound44]

Here’s the schematic for a gyro to be used with a Raymarine autopilot

https://www.cruisersforum.com/forums...5&d=1303090913