Are control systems and motors typically driven from the same source in robotics projects?
You'll usually have one main power source to the project.  Having multiple sets of batteries (A batteries for the filaments, B batteries for the plates) went out of style decades ago.

You want LOTS of decoupling between the microcontroller supply lines and the stepper supply lines.  Ditto the microcontroller and the stepper driver board supply lines.  Stepping motor coils are good inductors (DUH!), and they throw BIG spikes back at the controller when they are switched.  You do NOT want those big spikes to get back into your microcontroller supply.  Bypass capacitors and filter capacitors, conservatively rated, are your FRIENDS.

Stepping motor driver design is a Black Art.  It is not unusual to see a 12V stepping motor being driven from a 50V supply, as this allows creative design to minimize settling time.  The old Airpax stepping motor catalog had some REALLY good design information on this.

In this day and age, decent quality cheap switching power converters are easy to come by.  For a battery-powered system, these days, I'd look for one of these, in preference to the old 7800-series linear regulators, for the microcontroller supply.