IMU (inertial measurement unit)
Overview
The IMU’s job is to assist with measuring:
- Orientation/Yaw - which way is the tractor heading
- Pitch - how up or down the front of the tractor is
- Roll - how much the tractor is leaning left or right
This information helps immensely with improving accuracy in a single-GPS configuration. If you are going for a dual antenna setup, you won’t need an IMU as Yaw, Pitch and Roll are calculated by comparing the antenna postions instead.
IMUs exist in two main setups - an individual IMU component mounted on the PCB, or an IMU integrated into the GNSS module.
Module choice
The Adafruit BNO085 is typically the one to go for; it is effective, affordable and widely documented within the community. If you look at any kind of alternative, the pins have to be in the same configuration to fit on the AIO boards. Generally it is best to play it safe and stick with the BNO085.
These can be hard to find, so watch the Discourse or Telegram channels as helpful members often post when they see stock at $VENDOR.
In 2025 initial testing of the SYD Dyamics TM171 showed promising results. However, it is still in testing stages, so the BNO085 still recommended for most users.
Some users are also experimenting with the Unicore UM98/2 GNSS chip, which has an integrated IMU, with good results.
Adafruit BNO085
Installation
The BNO085 typically comes without header pins soldered - so you will need to source your own and solder them yourself.
The IMU then needs to be placed upright (like on the above picture), with X or Y matching up with the direction the tractor travels. You can orient it 0,90,180,270 degrees, configure X / Y, and invert accordingly from the software.