Estimated power pid

[andysc3]

How accurate is the power pid? I was logging it and it wasn't even close. Half the time it showed neg numbers.

[joecar]

CALC.POWER_RW calculates the net HP used to accelerate vehicle's mass after overcoming all friction components...

( i.e. it is a measure of the net power left over to accelerate the vehicle after all friction components have been overcome )

( it is an application of Newton's first 2 laws of motion )


it calculates the instantaneous rate of change of work on a mass: P = m * v * dv/dt

when the velocity is increasing (dv/dt is positive), the mass is accelerating (i.e. has net acceleration);
when the velocity is decreasing (dv/dt is negative), the mass is decelerating.

If you can accelerate faster, then it will produce a bigger number.


It shows negative numbers on deceleration (because rate of change of velocity was negative)...

if you log it accelerating up over a "good" stretch of road (net HP to accelerate), and then within minutes log it decelerating in neutral on the same stretch in the same direction (net HP consumed by friction losses), and then you create spreadsheet maps (HP vs MPH) and align them by MPH, and subtract the losses (subtracting a negative = adding the absolute value) you can estimate the flywheel power at each MPH...

(e.g. 250 - (-50) = 300)


It is only as accurate under controlled conditions and if the sampling rate was much higher

(for example, windshield mounted accelerometer/g-meters sample at 100 Hz).


Will it equal what you see on a dyno...? No (since you're accelerating the dyno).

Will it give you a relative indication of effectiveness of mods: yes/maybe, but only if the test conditions are strictly controlled.

Can it be inaccurate...? Yes, easily (especially if the sampling rate is low... 10Hz is low; 40Hz is ok; 100Hz is good).

Can it be accurate...? Possibly, with great difficulty (requires strictly controlled conditions).

Does it correlate to quarter mile ET/TS...? Possibly.

Does it require a Physics degree to apply it effectively: Yes.

[joecar]

So whether it produces meaningful results depends on how you use it.