I am trying to build an arm that will have about 5 by 5 by maybe 7 or so centimeters of room for a rotary motor capable of lifting it. The joint will basically allow the arm to rotate in a single degree of freedom in a circle that is perpendicular to the ground.The rest of the arm will probably be around 64 centimeters long and weigh around a minimum of 9 kilograms before it lifts anything.
What kind of motor type would give it the best chance of lifting the arm quickly† and reasonably accurately‡?
† Raising from straight down to out 90 degrees in around 1 to .5 seconds maximum.
‡ At least a centimeter at the end of the arm which means probably at the very least 300 positions for the motor.