I've noticed that the industrial robot arms have very smooth, fast, and strong movement. Does anyone know what type of servos they use. I'm trying to build my own and don't want to have the jerky movement that is seen in a lot of DIY robot arms? Thanks.
Universal states that they use brush-less DC motors with harmonic drives on their FAQ here http://cross-automation.com/blog/universal-robots-top-10-faqs
Bigger ones like the KUKA KR5 uses AC servo motors. From the conversation here https://support.industry.siemens.com/tf/ww/en/posts/kuka-servo-motor/87265/?page=0&pageSize=10#post344333 it looks it is a custom version of the Siemens IFK7 synchronous motor series. Many of these high end motors can have holding brakes, better quality bearings and drive mechanisms and very good control systems that prevent them from jerking like a DIY arm. In a DIY robot, joints are typically connected straight to the motor with no drive mechanism and the basic control system does not provide a lot of options for smooth motion.