X‐ray image quality for stop‐motion exposures is greatly affected by the system power capability. High power levels are required for adequate resolution, which often precludes the use of mobile x‐ray systems for stop‐motion exposures. Currently available mobile systems use (1) 90‐V nickel–cadmium batteries capable of 120 A, (2) a power line of 220 V ac, 60 Hz capable of about 100 A, or (3) a capacitor discharge unit using 1.0‐μF capacitors and limited to 17‐mAs equivalent output (compared to three‐phase systems at 100 kVp). In each case, instantaneous power is usually limited to 10 kW. An alternative means which now appears to be a practical power source for mobile x‐ray systems is the flywheel energy storage system. A 5‐kg flywheel has been constructed which runs at 10 000 rpm and stores 25 000 J while drawing only a few hundred watts to bring the system up to speed. When coupled to an aircraft alternator, pulsed power levels of 25 kW have been achieved. The aircraft alternator also has the advantage of high‐frequency output which has permitted the use of smaller high‐voltage transformers. This system permits the generation of powerful x rays using low‐power sources, such as single automobile batteries, common 115‐V outlets, or electrical sources of poor regulation such as found in third world countries.