I'm using blender to create scenes and export the scene to my game engine. I've managed to do this with .obj files by exporting the scene and flipping the axis (Y-up), which works nicely.

Now I want to export physics to my game engine by exporting the .bullet file but the problem is that the object transformations for all my game objects are on the blender axis (Z-up).

Is there a way of exporting the physics as Y-up as I can with the .obj file? (or ideally adjusting blender to be Y-up instead of Z-up, which I doubt)

Bullet, like a lot of scientific and engineering apps and Blender itself, uses Z up. No idea what is in the .bullet file, but likely you will have to transform the coordinates when you export them. Or process the file afterwards.

There is no nice way to change the Blender coordinate system.

Thanks. I managed to get the result I wanted by rotating the entire Blender scene around the origin and on the X axis by -90 degrees before exporting the .bullet file then exporting the .obj as Y-up -Z-forward.