A robotic surgical tool includes a drive housing having first and second ends, at least one spline extending between the first and second ends and including a drive gear that rotates with rotation of the spline, and a carriage mounted to the spline. A closure tube extends from the carriage through the first end and has an end effector arranged at a distal end. An activating mechanism is housed in the carriage and includes a driven gear coupled to the drive gear such that rotation of the drive gear rotates the driven gear, and a carrier arranged at a proximal end of the closure tube and coupled to the driven gear such that rotation of the driven gear moves the carrier and the closure tube axially along a longitudinal axis of the closure tube. Moving the closure tube along the longitudinal axis closes or opens end effector jaws.