Why would you want to buy steppers when you've already got servos? You can run brushed servos with the Gecko G-320 drives, which will operate from step-and-direction signals. Since you're not locked into any proprietary drivers, you should be able to use an open-source controller like ROS: ROS-Industrial: open-source software in industrial robotics This downloadable software also looks interesting: https://sourceforge.net/projects/armcontrol/