Both locos pull the same train: 22 LHB coaches, about 1050 t, on level track.
Auto is a flat-out start on a clear main line: no wheel slip, crossovers or brake release to wait for. Real drivers start more gently, but both locos skip the same things. This is an illustrative model, not a certified simulation.
Steps of 0.1 kV; hold a button to keep going. 16.5 converter minimum · 22.5 WAP7 full power · 25 nominal · 27.5 max continuous.
Each notch moves the tap changer one step. The MPS lever weakens the motor fields, from notch 20 up.
Push forward for tractive effort (TE), pull back for braking effort (BE); this run only uses TE. The driver asks for a share of the maximum pull and the converters work out the voltage and frequency.
Why the WAP4 line is a sawtooth. Each notch fixes the DC voltage. As the train speeds up, the series motors generate more back-voltage, so less current flows; and because their field is made by that same current, the pull falls even faster than the current does. Taking the next notch lifts the voltage and the current jumps back up. The WAP7's converters re-adjust voltage and frequency hundreds of times a second to hold the pull you asked for, so its line stays flat until it reaches its power limit. Passengers don't feel the WAP4's teeth: each notch adds only about 10 to 50 kN, a change of a few hundredths of a m/s² across a 1160 t train, and the pull then fades over several seconds. The series motors also damp surges, because their pull drops as soon as the loco runs ahead of the train. The WAP7's torque control holds its pull steady instead, which is partly why a hard WAP7 start or regen can feel jerkier.