Jason, Gigio and I just got back from a day of test flying four ArduCopters, which is the most we've ever had out at one time. These were of different designs, with different props, motors, ESCs, batteries, frames etc. The point was to try to see why some people have great-performing ArduCopters and others have issues. We assumed it was due to hardware differences, but we needed to test to know more.

Unfortunately, the wind was around 20Mph, gusting to 30, so it was a pretty tough environment for flying. Serious stress testing! We had our share of "hard landings", but all quads lived to fly another day.

Here's what we learned (and are doing):

  1. Quads with the gyro filters enabled do seem to fly better, but this seems to be most obvious only if they've got vibration issues to begin with.
  2. Balance your props! Out-of-balance props lead to vibrations that can cause IMU errors to accumulate, leading to the "I have to hold the stick all the way over to stay in place" problem. Jason is going to put a better software filter on the accelerometers to try to compensate for that, but the main difference between good-flying quads and bad-flying ones seems to be vibration.
  3. While you're at it, double check that your motors and props screws are tightened down. Check them often. We had one motor fall off in flight (d'oh! It wrapped itself around the one arm on way down and pulled out a wire. need a new motor now) and one prop fly off. One of those (the former) was mine, so I feel pretty dumb about not checking.
  4. We've fixed that bug where the quad gains altitude quickly in alt hold at the transition between using the sonar and the baro sensor. That will be in the next code pushed in a day or two.
  5. Position hold ("loiter") in 25 mph winds is hard ;-). Jason is going to tweak the algorythm for that situation, where the quad has to tilt by 20 degrees just to fight the wind. That's near the max angle of tilt in the code, so if it gets blown downwind, it can't tilt further to come back. For these kind of steady-state tilts, he's going to allow it to tilt further to return to position.
  6. Something I learned: if you want to reset "forward" in Simple mode, just disarm the motors, point the quad in the direction you want forward to be and rearm. That will reset the direction.

 

Jason is going to be releasing 2.0.24 in day or so. If that solves most of these issues and passes beta testing, we'll take AC 2.0 out of beta!

 

 

 

 

 

 

 

Views: 388

Comment by emile on June 13, 2011 at 4:27am
Chris, neither of you ever had Yaw issues? It seems I can't get my quad with stable yaw. It goes left and right without stick input. It also seems that right is more powerful than right... I tried every configuration possible, checking motor balance, Mag and what so ever.
Yesterday I have experienced another strange issue. Giving full right had no effect on yaw, while a slight left was very powerful. When leaving controls the quad was quite stable. While writing, something comes to my mind. Could it be the saturation experienced in the roll/pitch drift, only applied to yaw? Will try to solder the pads today.
Cheers,
E.

3D Robotics
Comment by Chris Anderson on June 13, 2011 at 7:11am
Emile, I haven't experienced the yaw issues myself, but enough other people had that we were able to diagnose and make some changes. Look for a new version of the code today or tomorrow.
Comment by robert bouwens on June 13, 2011 at 8:00am

@emile

you need to play with kp_rollpitch.

not lowering but much higher. then you solve the gyro offset problems.

 

i lowered the yaw settings because of overshooting.

now it is stable - with regards to yaw.

Comment by emile on June 13, 2011 at 8:13am

My quad has never been so stable regardin roll and pitch. I would say it is almost perfect! No wobbles, no descent instability just nice and firm. Also never had drift problems like others, but only yaw is making me a little mad...

BTW my PIDs with KDA 20-22L and custom frame (AC clone) are: P:0.4 I:0.24 D:0.17 these are maybe a little "not fun to fly" but are giving me the best in terms of stability.

I tried different Yaw PIDs but never got succesful. 

Anyway thanks for the suggestion!

Cheers,

E.

Comment by robert bouwens on June 13, 2011 at 8:56am

the yaw pid settings are the one you of interest.

but thanks for the pid settings as i have a couple of kda 20-20 in the back.

will try these settings.

# define STABILIZE_PITCH_P  0.48
# define STABILIZE_PITCH_I   0.1
# define STABILIZE_PITCH_D  0.11
these are the ones i am using - somewhat to high but stabilize was nice.

did play with kp_rollpitch not with the averaging buffer.

cheers

robert

Comment by Chris Starke on June 13, 2011 at 9:34am
Nice to see the code moving along. One problem i do have with the current code is that i live in cape town south africa and the magnetic declination here is 24 degrees and in the current code it is not possible to put in more than 15 degrees.
Comment by Chris Starke on June 13, 2011 at 9:40am
whoops its actually -24 but still the same problem
Comment by robert bouwens on June 13, 2011 at 9:43am

@emile

when i flew with stock yaw pid settings then yaw overshoots without doewing anything on yaw.

to solve this i need to drastically reduce the i and d term for yaw.

that works nice for the small jakub frame.

cheers

robert


3D Robotics
Comment by Chris Anderson on June 13, 2011 at 10:12am
ALL: please try the new code (2.0.24 alpha) that Jason has posted here:
http://diydrones.com/forum/topics/arducopter-2024a-alpha?xg_source=...

Lots of changes and improvements. We need more alpha test feedback before we'll feel comfortable pushing it out as a hex for all the beta testers, so please try it and let Jason know in that thread how it works for you.

Moderator
Comment by Mark Harrison on June 13, 2011 at 11:57am

-1 prop saver:  I've built a new model with 1300 kvm blue wonder motors, and am using the prop savers until my 3mm prop adapters arrive.  They definitely make it hard to eliminate vibration... each flight it's necessary to spin up the props and fix the wobblies.  I'll still use them on my fixed wing planes for now... it seems a lot easier to get one prop spinning smoothly than four at a time.

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