But it remains hard to shrink engines, batteries, mechanical actuators and control electronics to the point where they are small and light enough to fly without impairing their performance.

• 升空的运作过程，必须要有像磁浮列车等大型机器常用的磁场，磁场相斥或相吸，而且磁浮列车需要某种导轨或缰绳导控机器，免得飞太远或出轨。