The Pendulum Whiteboard Printer is a fully-automatic robotic device for marking or otherwise effecting whiteboards, pinboards, or other vertical surfaces. The physical device consists of an effector platform suspended by two suspension wires whose lengths are adjusted by motorized spindles mounted above and on either side of the board surface. The position of the effector platform is adjusted by winding and unwinding the wires. Electrical power is supplied to the effector platform through the suspension wires or through an on-board battery. Control of a pen and/or other apparatus on the effector platform is achieved through modulation of the power voltage. A further component of this invention is electronic and computational apparatus for controlling the device, which may include automatic visual interpretation and feedback from a video camera viewing the board and printer.