ELSIE (Electro-mechanical robot, Light Sensitive with Internal and External stability ). The press at the time reported the arrival of ELSIE in late 1949, eg Daily Mail, 17 November 1949; and Daily Express, 13 December 1949. But a memo exists from Edison Swan to Grey dated 10 Mar 1948 suggests that the female tortoise [ELSIE] was also built in 1948. [Note: Edison Swan was the company Grey Walter and the BNI used to construct their many instruments.] 
It has not been mentioned before but there are several variants of ELSIE, each with subtle changes. The images I will present below and continued into the next blog entry will highlight these variations. Although difficult to see different componentry and circuitry, the observable differences are around the capacitors, and the relays. The earliest version of ELSIE that I have seen utilises twin-coil relays. The later single-coil relays are also used in the later 1951 batch of 6. This first batch of 5 pictures are of similar (if not the same) version in terms of mechanicals and relays. Here they are: 
to be continued next post in this category…ELSIE – Upgraded.