like, even if we choose the universal motor...theres a prob as u noe, torque = current x area x magnetic field x no of turns...
increasin either wud cause a prob except for increasin magnetic field n for that again we need high electricity supply n thats possible is we use mini batteries same as aircrafts as they are light weight, n high output providers...but expensive
still for the thing, using nano or micro-tech building universal motor wud be best idea as they r 1 of the most effecient output providers