IMU placement

[jhoop]

Hello everyone
I'm wondering how and where you all put you IMU's?
I would like it as close to centerline and center of gravity but I know that it can't handle the long wire run.
Do you use an ESP8266 or ESP32 to get the data to the Pi? But then I read that there is a lag in the data.
How to you compensate for where it is usually located, close to the Pi? Or it doesn't matter in the real world.
Thanks
Jim

[baltika_no_9]

Hello everyone
I'm wondering how and where you all put you IMU's?
I would like it as close to centerline and center of gravity but I know that it can't handle the long wire run.
Do you use an ESP8266 or ESP32 to get the data to the Pi? But then I read that there is a lag in the data.
How to you compensate for where it is usually located, close to the Pi? Or it doesn't matter in the real world.
Thanks
Jim

I would imagine that the delay you mention is to a large extent under your control if you are using the IMU attached remotely via an ESPxx. In the sketch you can define how how frequently the ESP sends updates (via MQTT or whatever your chosen protocol might be).

In terms of physical placement I'm not certain it matters to any significant degree although of course you should keep it away from sources of magnetic influences such as high current carrying cables and ferrous components.

[seandepagnier]

The delay is not acceptable for an autopilot, especially if you have a pi receiving it since the wifi can have random lags that are significant. A dedicated esp32 to esp32 link may be acceptable, but this has not been proven.

The location of the imu is not as important as you think as for putting in the center of the boat. Obviously putting on top of the mast, or the very end of the boat is not ideal, but the accelerometers most affected by this are the least important sensor.

The most important part is to keep it away from magnetic distortions such as speakers, compass, other magnets, current carrying wires etc. If you are really concerned, it is common to use a pi zero for the imu and autopilot, then the pi with openplotter just gets this data over wifi and there is no problem, and both can be placed more optimally.

[yiannis]

I know I am re-opening an old post, but I am trying to keep things simple and avoid using ESPs etc.

So my question is: do I have to keep the IMU away from AC current or even the low DC current that we have in the enclosure of the Raspberry Pi?

I remember seeing a position for the IMU in the new MacArthur HAT and it seems to be right bang in the middle of all sorts of components and near the MAIANA connector which is high frequency. Right?

I have this enclosure.
   

Top right is the SSD. I have space in the areas marked 1 and 2. I use cable-ties to secure the boards on the bottom, rather than metal screws (easier, quicker, they don't corrode and less ferrous metals to interfere with the compass).

So, would it make a big difference if I put the IMU in area 1 or 2? Or should I try something completely different?

I am open to suggestions.

TIA,
Yiannis

[mgrouch]

Put IMU into separate small flanged box. Run i2c wires to your main box.
You would need to calibrate IMU and for that you need to rotate it in all directions.
It’s not convenient to have it in big box.

[Techstyle]

I had issues with mine being correct on one tack, but totally wrong on the other tack.  I swapped the IMU thinking it was that but the new one had the same issue.  I tried a new location and that changed the issue slightly and then I moved it to a third location and now it works great.  The thing that mostly changes was the angle of the board to the boat.  The IMU is now 5ft back from the center of pitch and 5ft Starboard of center of roll.

I agree with MrGrouch, make it separate to aid calibration and be prepared to move it around a bit

[PaddyB]

So, would it make a big difference if I put the IMU in area 1 or 2? Or should I try something completely different?

I mount the 9doff seperately using a cat5 cable. I2c is only designed for short distance so cat% on it's own wasn't stable, this hack has solved that (so far....)
rj45 breakout boxes can be found on ebay or if you like a fiddle the cheap little socket/socket things can be taken apart & soldered, though wires are short.

https://youtu.be/6v1KZBRZRCI?t=171