Member "Dajiu" disabled his R3 Roomba by placing each cliff-sensors IRED & PT side by side, taped together as I recall, about four years ago. He posted that achievement in this rr thread: viewtopic.php?p=58152#p58152
but rather than detail what he did, as well as provide a great step-by-step procedure about taking the R3-Roomba apart in order to reach the sensors, he built a web-page at this address to hold that information: http://www.pottsland.com/roomba/Roomba_ ... ensor.html
Now, a comment: From an opto-electric view point I am certain that Dajiu's side-by-side coupling of an IRED with its PT partner is more desirable than beaming IR radiance directly into the PT, for the reason that side-by-side coupling tends to mimic the considerable attenuation normally experienced by scattering the IR signal off flooring materials. IOW, the detector portion of a Cliff Sensor is expecting a low level return signal, not the high strength of source radiance. Notice I said "desirable", not superior.
Good of you to post, Andy. Your thread title may be easier for searchers to find than Dajiu's.