Discussions

Hello all!

I had the time yesterday (and guts) to see how 2.8.1 would do in high wind situations and thought I would share my experience with everyone as I was over all impressed.

Conditions:

• Overcast
• Temperature: 60-70 F
• Wind was out of the SSW at 30-35 mph
• Gusts up to 50 mph

Flight Agenda:

• Two 9 minute flights where stab, alt hold, and loiter modes are tested
• 3rd 9 minute flight where stab, loiter, and RTL modes are tested
• 4th 9 minute flight where auto mode is tested

Stabilize Mode:

Flew well, comparable to with light wind. Not a huge difference in handling seen between 10mph winds and 30mph winds other than the amount of correction needed to stay in place.

There were only small wobbles when the strongest of winds came up. I was able to make roughly 2-3m/s directly into the head wind at full throttle. Much throttle manipulation was needed to keep a steady altitude while moving into the wind as the gusts would cause the drone rise and fall, as well as the need to apply more power as you head into the wind.

Overall pretty acceptable considering the conditions, was fairly comfortable to fly - if not a bit thrilling. =)

Alt Hold Mode:

Alt hold also worked well - comparable with a light wind. Not a huge difference in handling seen between 10mph winds and 30mph winds other than the amount of correction needed to stay in place.

Using alt hold to fly into the head wind resulted in moderate altitude lost while traveling into the head wind at full stick position. The movement into the head wind would need to be stopped every 7-10m due to altitude loss (3-7m) to allow for alt hold to compensate and then return the the specified height.

Flying in directions that were tangential to the head wind posed much less problems keeping altitude, but were somewhat affected.

The high wind gusts (40-50mph) would cause altitude leaps up or down 1-2m but they were usually compensated for quickly when manually holding position - However not so quickly compensated for if moving.

Other than the issue with keeping altitude, alt hold performed well.

Loiter Mode:

Loiter was pretty amazing, really, considering the conditions.

I was able to loiter in a 1-2m area in the constant winds of 30-35mph. (alt hold of +- 1m most of the time). 

When the high speed gusts came the drone did get blown around moving +-1-2m of altitude and up to 10m in horizontal distance from the loiter point. When blown from the loiter point it would work its way back but never really back to where it was but somewhere within 2-4m. Im assuming that this is due to GPS accuracy vs anything else? 

The drone was wobbling a bit slowly trying to keep stable but again all in all not bad and with some onsite tuning was able to improve some (Not as stable as stabilize mode tho.)

But over all the drone performed very well, considering the high winds.

RTL Mode:

RTL was not as impressive as loiter.

When RTL was invoked the copter would start to very rapidly move in the direction of the wind (10m/s+). Eventually it would stop having missed home considerably and try to crawl its way back.(It was kind of cool to see it move this fast)

In crawling its way back the altitude will fluctuate considerably while moving against the wind dropping slowly heading into the wind until it would nearly hit the ground and then slowly and come upwards again, a 4-8m variance is seen. These dips were pretty extreme causing some near ground incidents - manual control to get it back up to a safe altitude. When traveling perpendicularity to the wind the affects on altitude seemed to be much less 1-2m variance.

However when all was said and done it usually got within 4-5m of home, which isn't great but acceptable.

It *appears* that RTL was thinking this: (My guess)

• I need to be at xyz coords (home).
• That's north 50m and west 50m.
• Lets go north at 5m/s (+ wind velocity).
• Wow going fast now.
• Almost there Ill start slowing down. Hmm there seems to be quite a bit of wind.
• Opps I way overshot the north 50m mark and still need to get over to the west by 50m
• Let me head south again abit while heading west to home.

Auto Mode:

This was bad. I set a pretty simple course east/west which was perpendicularity to the wind direction, the drone was to fly east-west 3 times and then return home.
I flew the drone up to 10m (which was the missions alt) and put it in auto mode.
It then took off toward its waypoint but descended into the ground before I could stop it. (I was watching and hoping it would catch itself).
The drone flew about 34m and descended from 10m to ground in that time with no sign of a correction. 
Luckily it was 1 and 1/2 foot field grass so only about 10$ worth of damage.

Thoughts:

Overall I was pretty impressed. Honesty with how strong the wind was I thought I would take the drone out and it would flip over in the 1st strong gust, however I was proven quite wrong =).

In loiter mode at one point a strong gust came up and blew my hat down the road and the drone only moved about 3m and got back to nearly where it was pre gust. (Also I kept it up during a brief shower that was about 2 minutes long and pretty light).

So pretty good in my book =)

However, as good as it is, there is room for large improvement in the altitude hold while heading into the wind or flying in wind. The good news is that seems to be simply software(algorithm) or pid tuning, as in stab mode the copter was able to maintain altitude fine to a variance of ~1m - granted with heavy throttle control.

Questions:

• Has anyone else tested in similar conditions? (Where I live we frequently get this type of wind and even higher say up to 70mph during rough storms.)
• As I'm still learning how the pids affect different copter behavior, does anyone have any thought on if there is tuning that could be done to help with the altitude hold while moving into the wind?
• Is this similar to adding more weight to your copter - more inertial resistance but only in a single direction?
• For the "return to original loiter point when blown from it" issue - Can position distance deviation be derived from the mag/accel/gyro data? 
  • Example:
    • Loiter is initiated (0,0,0)
    • Wind pushed drone to 0,-15,2 
    • Can I derive, with better than GPS accuracy, from the accel/mag/gyro how far I have traveled from 0,0,0 to return to it?
• In thinking about this situation does anyone have any idea if large props and lower KV rated motors would help the scenario of alt hold into the wind?

What could be improved:

• Altitude hold while moving into the wind needs to be improved greatly if possible
• RTL needs to understand that there is a constant force in a particular direction and understand how to compensate for it better and sooner than currently, while abiding to the over all speed limit set in MP.
  • IE. If MP says to move at 5m/s toward a way point I should not move at 5m/s (calculated) + wind speed.

Thanks all, hope this is useful or will generate useful discussion.

Setup:

APM 2.0

Arducopter 2.8.1

Sonar (XL-EZL0)

HK 550 Hex Frame

1200KV Motors (I know these are not the best choice)

9x4.7 props