A surgical instrument includes: a distal movable component; a proximal drive assembly including a drive shaft, a capstan, and a plurality of splines; a first cable extending between the distal movable component and the drive shaft; and a second cable extending between the distal movable component and the capstan. The drive shaft includes a tapered projection, and the capstan includes a tapered bore in which the tapered projection of the drive shaft is received. The plurality of splines engage the tapered projection of the drive shaft with the tapered bore of the capstan.