Medical robot systems, surgical tool assemblies, devices, and methods regarding the same. The medical robot system may include a robot coupled to an end-effector having a guide tube. The robot may be configured for controlled movement and positioning of the end-effector. The system further includes a motor assembly coupled to the robot. The motor assembly may be configured to move the end-effector along one or more of an x-axis, a y-axis, and a z-axis. The surgical instrument is positionable and/or slidable within the guide tube. The surgical instrument includes at least one detectable feature, such as a reflective lens or stripe. A detection device is configured and arranged to detect the at least one detectable feature. The system enables a depth of the surgical instrument in the guide tube to be determined by the at least one detectable feature on the instrument.
