How to make APM work for tricopters so the tail doesn't "wobble"?

LitterBug

Troll Spammer
Can you download the last dataflash log through mavlink? Might be able to see what it thinks is going on.

Cheers!
LitterBug
 

Donnut

Member
Yes I tested by holding it with hand extensively. It really looks alright. And no disrespect but after some more reading I'm pretty sure that the servo should move the motor in the opposite direction of the yaw stick input.

I calibrated the ESCs, by
- turning radio on
- raising the throttle
- plugging the battery in the model
- removing the battery
- plugging the battery again
- moving the throttle down after the beeps (only odd thing is I didn't hear more beeps after moving the throttle down)
- unplugging the model
 

makattack

Winter is coming
Moderator
Mentor
Well, I see your esc calibration method might be problematic. I see you tried the apm, calibrate all at once method, but didn't get the confirmation tones. Did you run up the motors to test as indicated in the docs? The other option is to do them manually as described if you can't calibrate all at once:
http://ardupilot.org/copter/docs/esc-calibration.html

Also, you're not being disrespectful or anything like that about disagreeing with me, but your response leads me to think you still don't understand what I'm telling you about the yaw servo/motor. What I've been saying all along works for me and many other people. My tricopters running APM and MultiWii flies well and are super stable. I'm only trying to help you with what I know to be common problems with people setting up their APM based aircraft. Assuming correct setup and configuration, with working hardware, no tricopter should spin on the yaw axis uncontrollably. You might have drift on yaw, which might indicate a trim or calibration issue, but you should be able to override that with manual control. If it spins to the point where you can't fly it, something is setup wrong.

Watch my video again with the volume up. I show two different behaviors in the tests. One with the yaw stick where it does indeed move the motor top towards the opposite direction. The other with the stick at neutral, but picking up the tricopter (again, no rc sticks/all centered) and yawing it around. It now will move the top of the motor in the same direction of the yaw action to OPPOSE that uncommanded yaw. You see, the apm should be in stabilize mode, and work to keep it level and straight. If it doesn't, then something is reversed and it doesn't know that so it will keep trying to change directions in the wrong direction. This is why it would spin in circles or flip upside down. This is also why you need to connect it to the ground software and observe the orientation to verify.

Ultimately, all that I describe is trying to allow you to test safely without the props on. If you exhaust all those options, then by all means, mount the props, run up the motor, and do the same tests carefully. Hold the tricopter in your hand, then move the various controller sticks on the roll, pitch, yaw axis and you should feel the corresponding behavior correctly. If not, something is setup wrong. Similarly, with the motors and prop running, and NO STICK input, if you roll, pitch, and yaw the tricopter, you should feel it OPPOSE or try to correct that action. If you roll/tilt it right, it should try to tilt/roll left. If you pitch it forward, it should try to pitch back. That force won't be constant as you can certainly override it by hand, but you should feel that initial opposing force when you first move it. Same with the yaw axis. Yaw/spin it clockwise, it should try to spin counterclockwise to oppose it initially. That's what stabilize mode is. Now, how hard and for how long it tries to oppose your action is what those PID constants affect. Similarly, any oscillations you feel will be from too high a P value (or too low a D, or too high an I, etc... they're all related)

Anyway as litterbug indicated, logs would be most helpful. I would also add, if you can create a video that duplicates exactly what I did in my video, that would help in eliminating this question of whether you configured yaw servo reversal/configuration set properly on your TX AND on the APM.

Personally, if I were you, I would work on the following:

1) Making sure my ESC's are identically calibrated for the throttle range. Read the manuals on them to find out what the procedure is (if they can be calibrated, even)
2) Double/triple/quadruple-check everything as per the APM setup guides. I suspect your roll/pitch setup is ok, if all it does is spin on the yaw axis. If it's just doing that, I suspect you've got the yaw configuration wrong.
3) Don't fly it until you're sure of everything and tested everything to the fullest (checking the ground station, etc). If you don't do that, you'll just end up potentially damaging stuff.
 
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