Add support for BNO055 9-DOF IMU

[thall4]

Needs to be able to detect if we run into something and stop moving, and then adjust course accordingly. Doesn't have to be anything fancy, like:

if (x_accel < 0 && motor_direction == forward)
reverse();
delay(500);
leftturn();
delay(200);
forward();
//normal operation follows

[iansan5653]

The new IMU you ordered is a 9-axis. Is the 345 onboard?

[iansan5653]

We used an ADXL345 in the airbrakes. Relevant code:
Setup:
https://github.com/usfsoar/NSL_18-19_Airbrakes/blob/master/main.ino#L64-L69

Usage (about as simple as it gets; we just pulled y-accel):
https://github.com/usfsoar/NSL_18-19_Airbrakes/blob/master/main.ino#L192-L195

[thall4]

I filled this out before I decided to order another sensor, the new one I ordered has an embedded gyro which will make it more useful probably.

[iansan5653]

Yeah the new one should support this feature as well as compass. What's the new one called?

[thall4]

9-DOF Absolute Orientation IMU Fusion Breakout - BNO055

[iansan5653]

accel < 0 is not a good check btw; they would trigger any time the rover decelerates, ie, if it's climbing a hill. Not sure what the new IMU supports but some sort of significant spike in negative acceleration would be better (unless the IMU supports something better I mean).

[thall4]

Yeah I know, that was me just spitballing a basic trigger off the top of my head

[iansan5653]

Started a branch feature/imu with a draft pull request so we can add the feature over time with multiple people working on it.