Hi OkadaKeisuke
Ok, so it is an ARF. But you installed all of the components. Longer engine mount to move engine forward. Flat battery instead of conventional battery so it fits in a tight place. I once added a second battery and second switch for CG control, and gained more reliability. It is true that sometimes there is no choice but to add weight. I look at it as a personal failure if I have to add dead weight.