I wanted to start a conversation around the roll and pitch of Arducopter drifting as you fly.
The reason is I just assembled new hardware and problems that weren't there before have now shown up in a bad way. Flying indoors in a 5ft space I was able to get up to 30° error in roll and around 10-15° in pitch. I was able to control it and it flew perfectly level the whole time, I just had to hold the stick into the corner of the radio. Lading and waiting corrects the issue.
What could cause this. I had been flying an older version of the IMU this whole time. This version has an analogue filter for the gyros where the new hardware has it as an option. You must solder the pads around the gyros to enable them. I was also flying with two slightly tweaked motors giving off a lot of vibration. This could affect the accels.
My question is: If you have a problem like this, what is the vibration level on your copter, and do you have the filter pads soldered?
And notice I didn't say "loss of control" or "it didn't fly stable". I had control, and it flew perfectly. It just lost it's reference to the ground and I had to compensate with the stick. Had it been worse than 45° I would have lost control.
There are three pairs of pads, each with a white outline. (look for GYRO-XY near the relay).
Jani Solders his to enable the filter. I have never flown this board until now. I will solder them to test the filters this week.
Replies
Spent some time on properly analyse the data sampled from the gyros. I tuned the ADC library to allow 2000 Khz sampling and wrote a simple program to collect the data for various motor speeds.
As we can see from this data then there is considerable amount of disturbances above 500Hz.
The strongest peaks around 800Hz. Granted this is on my own quadcopter so disturbances could manifest them in different frequencies for different designs of quadcopters.
The main point is that _ALL_ of these disturbances will manifest them selves at lower frequencies due to aliasing when the data is only sampled at 200Hz like the standard ADC library does. (I know the code says 400Hz but it will never release a sample unless it has collected at least 2 samples with a very simple averaging filter, hence the 200Hz sampling rate). But even at 400Hz with this particular data we would have bad aliasing.
I would be very interested to see similar data from other quadcopters, both good and badly behaving.
Anyways I believe this is the main reason for bad behaving quadcopters. And the only real solution is to get rid of the high frequency disturbances before the data is sampled.
I attach my test programs and if any of you guys are interesting in supplying me with some data I can analyse it in a similar way. Please note though to only run this program with your quad on the workbench with NO propellers attached. The program will spin the motor with MAX throttle!
When looking on the graphs the two magenta lines are the approximate speed of the motor in Hz.
Please click on the image to see the animation.
aliasing.tgz
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
Two things that are new in 2.0.24 that I have found really useful (1 day of testing to go before I release it):
If you hold the yaw to arm or disarm the quad, you can keep holding that to get the in-field level or the auto-trim mode.
Hold to disarm for > 10 seconds = level the quad – the LEDs will cycle quickly and stop.
Hold to arm for > 20 seconds = Auto-trim mode for only 45 or so seconds – just fly in a no-wind situation and you can trim your quad by flying it perfectly still at about 3-4 feet. The will work in any mode, but for obvious reasons, use stable or simple.
Both modes exit automatically and the LED will flash in a pattern when in each mode.
Jason
I took my quad from near my home out to the FAR site in the Mojave desert.
I tried to fly it and as soon as I took off it tiped about 30 degrees to one side and full control input
was insufficient to level it out. The controls made changes, but full control deflection was insufficent.
It flew directly toward the larges chunk of concrete within 50 ftt and crashed on it.
I'm now impatiently awaiting parts from jdrones so I can fly it again.
This makes me ask the question could these instability issues could be environmental?
This was very early in the morning so the temp was not that different, but the altitude, and humidity were very different.
solder.png
Found the explenation of ch7 ;-)
Reply by jasonshort on June 1, 2011 at 12:08pmI actually have that capability in the code. It's commented out right now but easy to enable. The idea is that you fly in a windless environment, a large indoor space, then hold Channel 7 high and fly it until it's perfectly level. Accels are trimmed in flight based on stick input. It works great but people were flying with ch 7 high all the time causing issues.
uncomment this line in control_modes.pde :
//trim_accel();
Hi all,
any more updates on the effect of the jumpers soldered???
Dani
I just programmed my eurgles ch7. So from the rx I should connect ch7 to the seventh input on the APM?
puuh,
that soldering excercise delivers great results.
the copter is stable when jumping in the air.
have not flown to much - but the stability is back.
i reduced the i term for yaw - that gave nice results with no overshooting.
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