A modular infusion pump for dispensing a fluid, comprising: a curved reservoir module, comprising: a tubular, curved reservoir containing the fluid, the curved reservoir having a proximal end and a distal end ; a flexible drive train configured to slidably fit within the curved reservoir and to expel the fluid through the proximal end of the reservoir , the flexible drive train including: a plunger at a proximal end of the drive train , a cursor at a distal end of the drive train , and a plurality of balls positioned between the plunger and the cursor ; and a control module comprising an actuation mechanism comprising a lead screw configured to mechanically engage the plurality of the balls of the drive train when the reservoir module is connected to the control module and to drive_the drive train through the reservoir , characterized in that the flexible drive train includes a flexible and elastic filament extending between the cursor and the plunger , wherein the plurality of balls is positioned along and connected by the filament , wherein the filament is configured to maintain the plurality of balls under axial compression. a curved reservoir module, comprising: a tubular, curved reservoir containing the fluid, the curved reservoir having a proximal end and a distal end ; a flexible drive train configured to slidably fit within the curved reservoir and to expel the fluid through the proximal end of the reservoir , the flexible drive train including: a plunger at a proximal end of the drive train , a cursor at a distal end of the drive train , and a plurality of balls positioned between the plunger and the cursor ; and a control module comprising an actuation mechanism comprising a lead screw configured to mechanically engage the plurality of the balls of the drive train when the reservoir module is connected to the control module and to drive_the drive train through the reservoir , a tubular, curved reservoir containing the fluid, the curved reservoir having a proximal end and a distal end ; a flexible drive train configured to slidably fit within the curved reservoir and to expel the fluid through the proximal end of the reservoir , the flexible drive train including: a plunger at a proximal end of the drive train , a cursor at a distal end of the drive train , and a plurality of balls positioned between the plunger and the cursor ; and a control module comprising an actuation mechanism comprising a lead screw configured to mechanically engage the plurality of the balls of the drive train when the reservoir module is connected to the control module and to drive_the drive train through the reservoir , a plunger at a proximal end of the drive train , a cursor at a distal end of the drive train , and a plurality of balls positioned between the plunger and the cursor ; and a control module comprising an actuation mechanism comprising a lead screw configured to mechanically engage the plurality of the balls of the drive train when the reservoir module is connected to the control module and to drive_the drive train through the reservoir , characterized in that the flexible drive train includes a flexible and elastic filament extending between the cursor and the plunger , wherein the plurality of balls is positioned along and connected by the filament , wherein the filament is configured to maintain the plurality of balls under axial compression. <EOS>