Analysis: what stair training changed

The flat policy, the stair policy and the multi-terrain policy were compared step by step in recorded walks, on flat ground and on the stair lanes, to see where the stair policy's advantage comes from.

• The flat policy lifts its front feet 5.6 and 5.8 cm at the first two 3 cm steps, as high as Stanford's climbing policy (5.5 and 5.5 cm), and still crosses 3 times in 100 against 90: with the front feet on the steps its body pitch peaks at 35° in the median trial (Stanford's: 19°) and the trial ends
• The stair policy raises its steps on the stairs only: 4.6 cm on the flat approach, 7.3–7.6 cm at the second and third step, with a peak pitch of 20°
• On flat ground at a 0.5 m/s command the stair policy walks 0.39 m/s against 0.44 m/s for the flat policy, through a shorter stride (24.3 against 27.2 cm), with half the body bounce (6 against 12 mm)
• On the multi-terrain test course every policy passes 18 of the 34 tests 97 times or more in 100, so the scores differ on the other 16, mostly near-limit stairs