As the motor size increases, the motor controller becomes larger, a bit more complex and more expensive. The motor controller is connected to a micro or to a radio control system. The H-Bridge is a common form of motor controller. This consists of four electronic power switches connected between the power source and motor so that the speed and direction can be controlled. It's a trade between spending more time or more money.
Many people have trouble with reliability of larger home made motor controllers.
Mechanical design and layout become important as the currents increase. Microcontroller Almost any micro can be used. Generally, the faster it is and the more memory it has, the more it can do. One approach is to use one micro to do everything directly, another approach is to use a number of smaller micros, each handling a function, all connected back to a central controller or master. Typical micros are the HC11, PICs and Atmel chips among others.