The best way to gain experience points to evolve your brobots is Arcade.
However, this is also this way:
- Turn off any features on your phone which will automatically turn it off.
- Select a plane without homing guns.
- Select brobots you want experience points for, these cannot have homing cannons either.
- Start Level 10, Solo.
- Take out all Doom’s guns, except the right most.
- Position your plane to the far left. Somewhere between the OD button and the top most brobot special button works fine.
- Leave game on – experience points will be gained for the distance covered, which will amount to a lot if you leave it on overnight. But perhaps not very good for your phone.
Here is a video featuring Sparrow rank B, Cetus rank A, and Honeybee rank C.