Computer Science, Electronics, Electrical are more or less related. So whether to go for Mechanical or Electrical/ECE/CS. I think it depends upon what aspect one finds more interesting. The electronics and computing part takes care of the Control System and Signal Generation, but will not cover some of the complex mechanical aspects of robotics. So, one can choose CS/EE/ECE if he/she is more interested in the Signal Processing/Image Processing/Control Systems/Microprocessors/Circuit Design/Artificial Intelligence part, otherwise you can go for Mech