Looking for a tiny gear motor? Only from Solarbotics comes the GM15, measuring under 6mm (0.235") diameter, with an overall length of 20.1mm (0.79"), which is smaller than many pager motors! The output shaft is grooved for a 1.5mm radius belt, but we've easily modified it to mate with our 10mm RW wheel (drilled out to 0.086"). They weigh only 1.3grams! It's designed for 3V nominal operation, giving 920RPM drawing 100mA. At stall, you get over 0.49in*oz or 35.28gm*cm of torque! We're quite excited about these motors; they're quality made, inexpensive, and tiny! We expect to see lots of nano-sumo robots (25mm cube, or one cubic inch!) built out of these...