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dumping more INDI tuning knowledge

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qadmus 2020-09-03 23:18:06 -07:00
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Tuning.md

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# Lateral Tuning
### INDI tuning strategy
- Search Discord / Github for prior work on INDI tuning for your vehicle
- Vary one parameter at a time, by less than 10%, finding lower and upper edges of stability.
- Parameters are not independent, make it easy to notice improvements.
- Use a road you travel often and know well, with straights and curves, and excellent lane markings on both sides.
- Start with moderate values for outer (angle error) and inner (rate error) loops, like the Prius's outer 3, inner 4.
- Avoid instability: wobble, sloppy lane keeping, entering or exiting corners poorly, oscillating or jerky steering.
- Don't confuse tuning with poor planning from poor lane markings, or unexpected behavior from unknown roads.
- Start with moderate values for outer (error) and inner (rate error) loops, like the Prius's outer 3, inner 4.
- Avoid instability: over/underturning, early / late corner enter / exit, sloppy lane keeping, oscillating or jerky steering.
1. CRITICAL: Tune actuator delay first. Enter and exit curves dead center, no wobble on straights.
1. CRITICAL: Tune actuator delay first.
2. Tune actuator effectiveness. Lowest value without oversteering. May vary with speed.
3. Tune time constant. Lowest value with smooth actuation.
4. Tune inner loop (steer rate error gain). Highest value with smooth corrections on curves.
5. Tune outer loop (steer error gain). Highest value with smooth corrections on straights.
3. Tune time constant. Lowest value with smooth actuation. Avoid the noise of actuator gears thrashing.
4. Tune inner loop (steer rate error gain). Highest value that still gives smooth control. Effects turning into curves.
5. Tune outer loop (steer error gain). Highest value that still gives smooth control. Effects lane centering.
### Notes on INDI tuning parameters
* steerActuatorDelay
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* Crude
* If turning too early, decrease steerActuatorDelay
* If turning too late, increase steerActuatorDelay
* On straight section, vary in small steps away from best guess until the plan wobbles left and right.
* On straight section, vary in small steps +/- from best guess until the plan wobbles. Use mid-point.
* Fine
* Steer torque, pose yaw are proportional
* Normalize torque and yaw signals
* Normalize steer torque and pose yaw, which should be dependent but delayed
* Find median phase delay in frequency domain?
* Find maximum correlation of varying time delay?
* lateralTuning.indi.actuatorEffectiveness
* As effectiveness increases, actuation strength decreases
* Too high: weak, sloppy lane centering, slow oscillation, can't follow high curvature, high steering error causes snappy corrections
* Too low: overpower, saturation, jerky, fast oscillation
* Just right: just above fast oscillation
* Just right: Highest still able to maintain good lane centering.
* lateralTuning.indi.timeConstant
* Extend exponential decay of prior output steer
* Too high: sloppy lane centering
* Too low: noisy actuation, responds to every bump
* Just right: just above noisy actuation and lane centering instability
* Too low: noisy actuation, responds to every bump, maybe unable to maintain lane center due to rapid actuation
* Just right: above noisy actuation and lane centering instability
* lateralTuning.indi.innerLoopGain
* Steer rate error gain
* Too high: jerky oscillation in high curvature
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* Just right: brief snap on entering high curvature
* lateralTuning.indi.outerLoopGain
* Steer error gain
* Too high: twitchy hyper lane centering
* Too high: twitchy hyper lane centering, oversteering
* Too low: sloppy, all over lane
* Just right: crisp lane centering