'Desired' Turn Rate - Far from Desirable on Rover 4.3

[John_Easton]

My four meter craft is achieving the desired turn rate well, but the so called ‘desired’ turn rate is far from desirable.

Surely a truly desired turn rate should follow a straight line from waypoint to waypoint, not a drunken like wobble from wpt to wpt.

What parameters will bring the desired turn rate closer to the actual mission (straight line wpt to wpt)?

LOG - https://drive.google.com/file/d/1b4N3t4kdnz6QAyui3Ux5o0fPBNhYcGbu/view?usp=sharing

[Yuri_Rage]

Not a turn rate problem, rather a position control problem (the PSC_ parameters). Without a log, impossible to help further.

[John_Easton]

Apologies Yuri - forgot to put the link in … https://drive.google.com/file/d/1b4N3t4kdnz6QAyui3Ux5o0fPBNhYcGbu/view?usp=sharing

[Yuri_Rage]

I’ll have a look, but I make no promises. Tuning the position controller has proven quite tricky (and is actually holding up the stable release of Rover 4.3).

I look forward to @rmackay9’s analysis if he has a bit of time to provide it.

[Yuri_Rage]

Zooming to a section of the log where I think a straight path is being attempted shows a lot of position controller overshoots.

P is oscillating quite a bit while the I term is not saturating, and the D term is contributing very little (despite the noise), so I think reducing P is the ticket here. Maybe reduce PSC_VEL_P from 1 to 0.5 and see how that goes?

The rate tuning is somewhat well behaved, though there is quite a bit of noise in the speed controller. Reducing ATC_SPEED_P and I may help a bit with that.

[John_Easton]

Thank you for that Yuri. Do you perhaps have a link to detailed documentation explaining the tuning of the position controller for Rover 4.3? I really need to get my head around this.

Have a look at this section of the log where the throttle is almost shut right down for absolutely no reason at all. This throttle issue has been a hurdle from day one with Rover 4.3.

[Yuri_Rage]

I’m not sure I can fully explain that behavior, but I suspect it’s related to the poor navigation performance/position controller tune.

Here is the documentation for tuning 4.3 nav:
Tuning Navigation — Rover documentation (ardupilot.org)

[John_Easton]

@Yuri_Rage

I’m not sure I can fully explain that behavior, but I suspect it’s related to the poor navigation performance/position controller tune.

Thank you Yuri, I hadn’t noticed that it had been added.

[John_Easton]

We have major progress, the documentation on setting up Rover 4.3 works as advertised and is very exciting for large rover owners.
LOG - Dropbox - 00000013.BIN - Simplify your life

I followed the Rover 4.3 instructions here and it works perfectly for a simple East, South, West, North mission with 90 degree corners. Once I get the throttle sorted out I will do a typical shoreline contour mission and see how that goes. -

• Adjust these parameters to improve the vehicle’s tracking along the lines
  • set PSC_VEL_I and PSC_VEL_D to zero
  • increase PSC_VEL_P until the vehicle tracks the corners nicely without oscillating in the straights
  • increase PSC_VEL_D enough to make the corners more responsive but without introducing oscillations in the straights. This should normally be not more than 10% of PSC_VEL_P
  • set PSC_VEL_I to 20% of PSC_VEL_P
    
    

The only part I’m still having difficulty with is the throttle control as the craft is over throttling as it comes out of a turn where the desired speed looks right, but the achieved speed is overshooting.

Factors affecting the path include:

• The vehicle will cut the corners but will always try to pass within WP_RADIUS or TURN_RADIUS (whichever is larger) of each waypoint
• The vehicle will cut the corners more at higher speeds
• The vehicle will cut the corners more if the maximum accelerations are reduced (e.g. the lowest of ATC_ACCEL_MAX, ATC_DECEL_MAX and TURN_MAX_G * 9.81)
• The vehicle will slow down in the corners if necessary to pass within WP_RADIUS of the waypoint without exceeding the maximum accelerations (e.g. the lowest of ATC_ACCEL_MAX, ATC_DECEL_MAX and TURN_MAX_G * 9.81)