A few projects similar to Quad-a-ball have been built in the past. There are two notable research papers in the field: Hytaq, a vehicle from the Illinois Institute of Technology, and Gimball out of Ecole Polytechnique Federale de Lausanne.
Quad-a-ball differs from these two prior research vehicles in that it is the first triple-axis spherically-enclosed quadcopter capable of carrying payloads (eg. larger than a microcopter)
