So your tilter is struggling to push forward more then 7 cubes? This seems like an issue with the tilter geometry, gear ratio, and/or the motor cartridge. It would help to see a picture of the tilter so we can help. I know that lots of teams us a 1:7 torque gear ratio, with either a 100 RPM or 200 RPM motor cartridge. As to how to work the geometry of the tilter check out this thread. Fixing the geometry or gear ratio should not affect the robot width wise and push it further out of the 18" limit.