Ian St.John Archer Archer.pdf The Archer robot consists of two functional units: an immobile target and a mobile robot. The mobile robot will seek out an immobile target platform that has two IR emitter systems mounted on it. One of the emitter systems will be constantly on and rotating. The other emitter will be stationary, and will pulse on when the rotating emitter reaches a set point. By measuring the phase difference between these two signals, the mobile robot will be able to determine its exact position.