DC geared motor mix standard 6 mm shaft at front commonly used in all robotics models available in 150 rpm (specific the rpm required while placing an order). Center shaft geared motors specifically designed for robotic applications offer a wide variety of options. Easy to use and mount, standard size for all rpm's, a huge variety of rpm's available, long durability and very affordable price with distinct features. These motors open a wide choice to fit with almost all wheels and chassis. Metal Gears inside thus low noise and high torque at shaft output.