ADDITIONAL TIMING CAMS
In addition to the four main timing units there are three more cams
On the left is a cam with a brass tyre wrapped around it for 240 degrees. This is fitted to a shaft running at 2/3rds the speed of the top/fast drums. Brushes run on the surface of this cam and enable sensing for one complete rotation of a top drum or 26 points as it is more normally described. During the 13 points of 120 degrees of dead time the carry mechanism advances the middle drums one position.
The two cams on the right have the same brush arrangement but in this case a circuit is only made for 1/26th of a revolution. One cam is fitted to the middle or medium speed drums and when in the appropriate position ‘primes’ the lower or slow drum circuits to advance at the same time as the next ‘medium’ or middle carry.
The third cam is physically the same as the one just described but is fitted to a bottom or slow drum shaft. It serves two purposes. If the machine tests all 26x26x26 positions and does not find a genuine stop this cam together with other inputs stops the machine from ‘going all around again’.
Its second purpose is to quickly bring the machine back to its ‘start’ position. With the ‘carry home’ switch activated, both carry mechanisms will operate together and both middle and bottom drums will rotate until the operator sees that the machine is approaching a ZZZ stop. The ‘carry home’ switch will then be turned off and the machine allowed to reach its ‘home’ position where all drive will then be removed.