3.2.7 Descend Protocol 2

 Descend protocol 2 occurs when the total length of the staircase to be traversed down

is longer than the critical length. The Andros is moved to the edge of the stairs and the

front auxiliary tracks are moved downward to catch the Andros as it crosses the apex of

the stairs. (Figure 3-8a) While this is occurring, the rear auxiliary tracks are moved

downward to help rotate the Andros down to the plane of the staircase. (Figure 3-8b) The

Andros is moved forward until the main tracks come in contact with the stairs, as seen in

Figure 3-8c. The controller uses the "end of world" capability of the stair counter

assembly to determine the edge of the stairs, as discussed in Chapter 2.3. The Andros is

moved further forward and rear auxiliary tracks are moved to a horizontal position. The

Andros is moved down the steps until the third to last step is reached. Then, the front

auxiliary tracks are moved to parallel to the ground plane, which allows the Andros to

make an easy transition to the plane of the floor. (Figure 3-8d) The Andros is then

moved off and away from the staircase.