Some time ago I started training and racing on tandem bike with visually impaired cyclist. I took part in training camps and several races. It is great adventure and big motivation. 

I asked myself if I can design tandem frameset. I set up some requirements and desing challenges such as:

-aerodynamic shape seatposts, 

-asymmetric chainstay, 

-shaft drive connecting two cranksets,

-thru axles, 

-flat mount brakes with aerodynamic covers,

-Sram Universal derailleur hanger,

-front and rear handlebars integrated with stems

First of all I took a pen and create some sketches. Well that's maybe not exactly true, but line art modifier in blender quite well can fake it

scene source: https://youtu.be/Q09wNDtAtVE

some components source: https://grabcad.com/max.morozov-2