The Role of Throttle Scheduling in MotoGP

At Circuit of The Americas, I was able to resume a conversation with Aprilia team manager Romano Albesiano by asking a foolish question. Having seen jerky, erratic operation of anti-wheelie systems of some non-factory bikes, I asked if this were an example of differences in software sophistication. The front wheels of factory bikes, by contrast, smoothly rose an inch or so off the pavement during hard acceleration and hovered stably there.

He replied that it was not. He said that the difference I was seeing was not a comparison between factory and non-factory anti-wheelie software, but was a consequence of the factories all employing throttle scheduling while non-factory teams rely on anti-wheelie. Erratic operation occurs as an anti-wheelie system detects a rising front wheel, cuts power, the wheel drops, and then rises again when power is restored. This repeating cycle only crudely approximates maximum acceleration through a series of mistakes and corrections. Throttle scheduling, by contrast, delivers continuous torque in correct proportion to local traction.

Every well-equipped team has conducted extensive traction mapping of all the circuits for many years. This has resulted from combining every cycle of operation of traction-control systems on the team’s bikes with the GPS coordinates of exactly where the loss of traction occurred. By easy calculation (knowing what transmission ratio and final gearing were in use at the time) this is converted into engine torque. Through either dyno data or use of an on-board torque-meter, this can be put into the form of a correct throttle opening for each point on the line through a given corner. This throttle opening is smooth and continuous rather than on-and-off.

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When the rider opens the throttle fully, the full amplitude of this map is executed, smoothly varying from point to point. Because the map “knows” the grip at each point on the track, full application of the map will lift the front wheel only very slightly and smoothly, causing the observed “stable hover.”

When a team spokesman has in the past said, “During the off-season we worked to improve acceleration” that did not mean giving the engine more mid-range. It meant improving the accuracy and sensitivity of its throttle scheduling. Such systems have been in use at least since 2008, and were common in F1 long before that.

In the past, before adaptive (self-learning) systems were banned, throttle scheduling self-adjusted during races to compensate for changes in tire properties, track surface, and temperature. With the present ban, riders must switch in such changes manually, based on information displayed by their teams on their pit boards. This conceptually takes us back to the 1950s, when GP bikes carried bar-mounted adjusting levers for fuel mixture and ignition timing (bear in mind that bikes today continue to carry an adjusting lever for gear ratio–the shift pedal).

The rider can also vary engine torque as he deems necessary. As he reduces throttle angle, the amplitude of the throttle schedule is reduced, while retaining its shape.

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