In your ROV setup, where exactly is the IMU physically mounted?
Hi @halaabu -
Maybe you’re asking generally, for non BlueROV2 vehicles? On the BlueROV2, the IMU is onboard the Navigator or Pixhawk autopilot, which is on the starboard side of the electronics enclosure, towards the front. The Autopilot orientation parameter is thus set to “Roll90.” ArudPilot allows you to specify the placement of this offset vs. the vehicle center of mass as well.
Hi @halaabu, welcome to the forum 
Usually there’s a reason for wanting to know something like this, so relative to what (e.g. the camera, the frame, the vehicle’s center of mass/buoyancy/control, etc)?
Measuring on the CAD model provided in the BlueROV2 product page (in the technical details section), the IMU is located here, relative to the vehicle frame:
That said, the tolerances of the frame and mountings mean those measurements may be off by a few mm or so.
It’s also worth noting that the magnetometers (used for compass heading measurements) are located at slightly different points on the Navigator board:
Hi - I have been searching through the forums, but could not find the answer, and this seemed like a fitting topic for the question: is there a reason or advantage for the ‘roll90’ orientation of the navigator/pixhawk in the BlueROV2 configuration? Or could the electronics tray just as soon have been rotated to be flat - which seems like a more “standard” orientation from copter/rover frames.
Hi @trylu, welcome to the forum
That design decision is from well before I started at BR, but some speculation from a couple of our R&D team members is it might be slightly preferable for cooling the electronics by natural convection.
I expect having it be flat should still work fine, unless your electronics tray is made from a material that’s subject to creep, in which case laying it flat may encourage it to bow over time, which could be inconvenient.
From Rusty:
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