Apparatus is provided, comprising first and second rails (140) and a pneumatic motor assembly (22). The assembly comprises a first motor subassembly (180), comprising a first-motor subassembly locking balloon (160), which locks the first rail to the first motor subassembly by inflation thereof； and a first-motor subassembly moving balloon (170), which moves the first rail by a mechanism of either inflation or deflation of the first-motor subassembly moving balloon, when the first-motor locking balloon is inflated. Assembly (22) additionally comprises a second motor subassembly (185), comprising a second-motor assembly locking balloon (165), which locks the second rail to the second motor subassembly by inflation thereof； and a second-motor subassembly moving balloon (175), configured to move the second rail by a mechanism selected from either inflation or deflation of the second-motor subassembly moving balloon, when the second-motor subassembly locking balloon is inflated. Other applications are also provided.
