I used 15x15x800mm carbon fiber square tube to build my frame.
It’s very durable,strong,and light. I build two quad 525mm and 650mm size as those pictures.
525mm quad’s weight is 1945g include 6S3P Li-ion battery, and over 60min flight time.
650mm quad’s weight is 2270g include 6S4P Li-ion battery, and over 50min flight time.
I think maybe it’s not the best frame,but it’s good for me.
For your reference.