So I made a drone since I’ve made other RC models before, and I’ve been learning about all the extra things that go along with drones. Such as the extra sensors, computer and software and firmware.
I really like the PixHawk but Mission Planner has bugs and it often doesn’t connect or freezes, or won’t allow the PIDs to be changed.
The Drone’s an X8 with 4 arms and two propellers on each arm, with one above the other.
In flight, or even just above the ground, it will often start descending, until the throttle stick is at the top and the drone even rocks back and forth a few times before meeting the ground.
The frame is rigid (carbon tubes and plates) and the flight controller is properly fitted with gel in the centre of the frame. No Bad AHRS or any other fail safes or warnings.
In the Datalogs show the motor PWM outputs going wild when the drone descends. Also in flight, some motors will go to 100% and others to idle!
I’m not sure what’s going on here.
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it sinks probably due to a local gravity anomaly.
would you like more wild guesses ? or prefer to post logs ? :)
I got the SD card working (Thank you) by formatting it and trying different Log bitmasks because some seemed unstable.
I also got the attitude to be stable with good control response by manually tuning.
Now the only real problem the drone has, is it will descend, for no obvious reason.
The PWMs from the PixHawk to the ESCs start to diverge (reducing over-all thrust) and their amplitude also gets a lot bigger, initiating a descent. From 6 meters altitude (above ground effect), and from a stable hover, at the end of the datalog on the right the drone just descended and no throttle stick input would arrest the descent.
CTUN ThO (not shown above) shows the PixHawk intended to climb, but the drone descended instead.
I'm going to try turning the PIDs down a bit, although only the kP is any value: kI and kD are very close to zero.
SO, I'm also wondering if turning UP kD will reduce the amplitute of the diverging PWMs. I just don't know why they are diverging. Yes I can see one motor is maxed-out and others are getting close to idle, I just don't know why. Its fine or 10 minutes at a time until this happens.
IMAX is also 0. – Can anyone explain what this parameter is and what its effects are please?
(I've read it limits the maximum I-gain, and I have Rate kI for roll and pitch at 0.06) (kI could do with being higher)
Stabilise or Outer PIDs are 4.5 for roll and pitch. What would turning them up or down do?
Any suggestions or recommendations are much appreciated :)
Thanks.
no, usually , you should have seen the folders be created, log started, it's common for it to abruptly stop logging on power loss. (and the logs are always useful until the last <second.)
Thanks Again Andre!
The Bitmask, I've been looking at Logs on the Parameter List
I just wasn't clear on what was being called a sync issue. I have not seen any sync issues from bench testing.
Can a faulty power module cause DataFlash Logs not to be saved?
for bitmask : use http://ardupilot.org/copter/docs/parameters.html , calculate the bitmask from that info if you are using current AC build.
Sync issues is something you can hear, sometimes smell :) , google it - watch youtube for examples - you want to see perfect acceleration of propeller at any rate of fast stickbanging, no hesitation.
dataflash: nothing appears on SD ? - try removing (if any) partitions on it, and formatting it with FAT32 - if nothing, not even directories spawn, having tested different SD cards, I'd say the pixhawk is bad.
DataFlash Logs are still not working (they have worked for a few months and last week they just stopped working).
Tested 2 SD cards and 2 USB cables today.
Tried the Log Bitmask settings.
Even re-installed the latest firmware.
And tried reading Logs with the QGroundControl
And still "No Logs to Download"
Hello Andre,
I'm not clear on your advice "calculate a decimal value, enter it, not rely on some GUI (which may contain bugs)".
Sync Issue: if I setup the bench test again with handheld Tx and Rx only, what am I testing for and what am I looking for?
ESC Refresh Rate: I have RobotBirds PRO but they haven't simply told me an answer to this.
"Using the tickboxes in the Log_Bitmask"
try another GCS, and calculate a decimal value, enter it, not rely on some GUI (which may contain bugs)
you have done the ESC throttle calibration ? - if your throttle stick at full throttle when you climbed slowly ?
I have been looking at the DataFlash Logs, at the motor outputs, some go high and others can go to idle! Sometimes the signals look very noisy.
And another new problem:
The DataFlash Logs won't stay saved when disconnecting the battery.
They were fine on the old firmware, but after an update, the Log_Bitmask tickboxes are different, the number in the Log_Bitmask on the Full Parameters List seems to change itself to a number not on the list in the box next to it.
So it's either now not saving Logs, or if I get it to stay saved after disconnecting the battery, the information I want, such as the motor outputs and altitude are not there! Using the tickboxes in the Log_Bitmask on the Standard Parameters list, seems to enter a random number in the Full Parameters List and then it won't log.
Hi Andrea K
I tested the motors and propellers on a test rig, with scales, with a normal R/C receiver, before building the drone.
The arm with 2 motors (co-axial) was giving 2.1Kg thrust at full throttle.
So, you'd expect 4 arms to give 8.4Kgs full throttle.
And for this to EASILY keep a 5.5Kg drone aloft.
Is it too marginal for 7.0Kgs? How about 5.5Kgs?
It seems in-flight, that the PixHawk is not outputting the same PWM to the ESCs as the basic R/C Rx did.
Or can you really lose that much thrust due to un-tuned PIDs?
Thanks!
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