A computer-assisted medical device comprising: a first repositionable arm having a plurality of first joints (215, 245, 315, 355), a plurality of first links (210, 220, 240, 250, 310, 320, 330, 350, 360), and a first distal end configured to support a first instrument; a second repositionable arm having a plurality of second joints (215, 245, 315, 355), a plurality of second links (210, 220, 240, 250, 310, 320, 330, 350, 360), and a second distal end configured to support a second instrument; an input control configured to provide movement commands for the first instrument; and a control unit comprising one or more processors, the control unit coupled to the first repositionable arm, the second repositionable arm, and the input control, wherein the control unit: determines first positions of the plurality of first joints (215, 245, 315, 355) and second positions of the plurality of second joints (215, 245, 315, 355); uses a first virtual model of the first repositionable arm and the first positions to determine a plurality of first virtual boundaries (230, 260, 340, 370) around the first repositionable arm; uses a second virtual model of the second repositionable arm and the second positions to determine a plurality of second virtual boundaries (230, 260, 340, 370) around the second repositionable arm; determines a first overlap between a first one of the plurality of first virtual boundaries (230, 260, 340, 370) and a first one of the plurality of second virtual boundaries (230, 260, 340, 370); determines a first overlap force on the first repositionable arm due to the first overlap; maps the first overlap force to first virtual torques on multiple first joints (215, 245, 315, 355) of the plurality of first joints (215, 245, 315, 355); determines a first tip force on a distal end of the first instrument based on the first virtual torques; and applies the first tip force as a first feedback force on the first instrument and the first repositionable arm. a first repositionable arm having a plurality of first joints (215, 245, 315, 355), a plurality of first links (210, 220, 240, 250, 310, 320, 330, 350, 360), and a first distal end configured to support a first instrument; a second repositionable arm having a plurality of second joints (215, 245, 315, 355), a plurality of second links (210, 220, 240, 250, 310, 320, 330, 350, 360), and a second distal end configured to support a second instrument; an input control configured to provide movement commands for the first instrument; and a control unit comprising one or more processors, the control unit coupled to the first repositionable arm, the second repositionable arm, and the input control, wherein the control unit: determines first positions of the plurality of first joints (215, 245, 315, 355) and second positions of the plurality of second joints (215, 245, 315, 355); uses a first virtual model of the first repositionable arm and the first positions to determine a plurality of first virtual boundaries (230, 260, 340, 370) around the first repositionable arm; uses a second virtual model of the second repositionable arm and the second positions to determine a plurality of second virtual boundaries (230, 260, 340, 370) around the second repositionable arm; determines a first overlap between a first one of the plurality of first virtual boundaries (230, 260, 340, 370) and a first one of the plurality of second virtual boundaries (230, 260, 340, 370); determines a first overlap force on the first repositionable arm due to the first overlap; maps the first overlap force to first virtual torques on multiple first joints (215, 245, 315, 355) of the plurality of first joints (215, 245, 315, 355); determines a first tip force on a distal end of the first instrument based on the first virtual torques; and applies the first tip force as a first feedback force on the first instrument and the first repositionable arm. determines first positions of the plurality of first joints (215, 245, 315, 355) and second positions of the plurality of second joints (215, 245, 315, 355); uses a first virtual model of the first repositionable arm and the first positions to determine a plurality of first virtual boundaries (230, 260, 340, 370) around the first repositionable arm; uses a second virtual model of the second repositionable arm and the second positions to determine a plurality of second virtual boundaries (230, 260, 340, 370) around the second repositionable arm; determines a first overlap between a first one of the plurality of first virtual boundaries (230, 260, 340, 370) and a first one of the plurality of second virtual boundaries (230, 260, 340, 370); determines a first overlap force on the first repositionable arm due to the first overlap; maps the first overlap force to first virtual torques on multiple first joints (215, 245, 315, 355) of the plurality of first joints (215, 245, 315, 355); determines a first tip force on a distal end of the first instrument based on the first virtual torques; and applies the first tip force as a first feedback force on the first instrument and the first repositionable arm.