jstremmler's bicopter

[jstremmler]

After changing the servos, adjusting the CG again….

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   20181031_134957.jpg
   

[jstremmler]

After changiong the servos, adjusting the CG again….

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   20181031_134959.jpg
   

[jihlein]

I’m pretty sure you are going to need to reverse the prop directions.

The oblique angle and prop rotation direction are critical to get the gyroscopic moment in the proper direction. Note in my pictures when pitching forwards the motors “pinch out”, and the left/right prop rotation is CW/CCW respectively. On yours, when pitching forward, the motors “pinch in”, which will require left/right prop rotation to be CCW/CW respectively.

[jstremmler]

@jihlein: Sure, that’s what I did. My mistake when building the bicopter was the wrong direction of the servos. (to the front of the copter) Unfortunately I only could remove one 3D-printed OATs adapter from the arm the other one was glued with CA… So I just turned the arm by 180° and installed the rest again. Flies great now. As motor 1 became now motor 2 and vice versa I even did not have to go to BLHeli_32 and change the motor direction….

[jstremmler]

Had a terrible flight today….
Reason was that I had switched off the accelerometer with SpeedyBee. Flashed Betaflight 3.5.3 in the evening and set up everything properly again. (including Angle and Horizon modes which had of course disappeared when switching off the accelerometer)

Btw. found a smart way to adjust the CG with the battery installed….

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   Bicopter-Balance.jpg
   

[jstremmler]

Yesterday I crashed my bicopter. After approximately 3 minutes in flight it simply fall off the sky. It looked like a failsafe and if the bicopter was just dropping to the ground. Unfortunately I didn’t have the SD-Card installed so that I have no blackbox data. Had to reinstall one Oats and one servo mount and to replace two props….

[Kevin_Erik]

Had this happen to me with Betaflights RTP check. After replacing both Servos i disabled this feature.

Runaway Takeoff Prevention (RTP) looks for conditions that are considered typical for “safe” flight. The intent is to prevent a runaway situation or the insta-crash upon lift off.

Usually the RTP check is done the moment a copter is airborn, stable and a preset throttle level is reached. Either it never clears the stability check and ends up disabling the copter randomly in flight.

Or

The throttle amount the Bicopter requires to hover is below the RTP threshold. Later as the Bicopter is flown, the throttle reaches 25% triggering the failure of RTP.

Here is what you need to know…
https://github.com/betaflight/betaflight/wiki/Runaway-Takeoff-Prevention

[jstremmler]

Yesterday I have flown my bicopter first time after repairing it.

Think the crash resulted from disabling the dynamic filter in Betaflight when it was crashing.

With dynamkic filter switched on it flies much better.

Was following Kevin’s advice and have completely disabled the runaway protection.

So far only misbehavior is an extreme pitching up when releasing my sticks. This of course the leads to an abrupt displacement of the CG which then in follow up causes some vibrations. But just by giving a little pitch forward vibrations can be eliminated.

Any advice?

[Kevin_Erik]

Things that can help…

When tuning Roll, tuning it exactly as if it were a quad-copter. Basically the behavior here is the same.

Yaw and Pitch however, needs much much less D-Term than what you would think. Apparently the Servos really aren’t fast enough to react to it well as all it does is over dampen the system. Granted thats what D-Term is for but not when the Servos respond to it so poorly. Thus far I’ve taken my D-Terms (Yaw / Pitch) to 10-15. I may even go lower should i be able to get the Pitch response curve to flatten out better. For your setup start with 35-40 “P” and “I” for about 15-20. The sloppiness you’ve seen is either the result of P overshoot or your I terms being too low. Trust me, you get too high on any of your terms and you’ll see it the moment you take off via oscillations from the ground effect making the copter go crazy.

Filtering, it pretty strait forward if your able to record your BF logs to an SD card. Initially you’ll want to set your Filtering to the defaults that are best suited for the Dynamic-Filtering, while keeping both the extra notch filters disabled. This will allow you to fly while still being able to see right where your noise is on the logs. After that set the Notch filtering as needed to cover the to greatest problem areas.

[jstremmler]

@Kevin_Erik: Well, so far I tried a lot of settings. David ones are much too aggressive and when I try yours, my bicopter fllies like a lame duck, like my quads have flown 6 years ago. Think this is not accepatble.

Actually I am flying with my PID parameters:
P I D FF
Roll 46 45 33 127
Pitch 50 50 38 146
Yaw 65 45 0 100

With these these PIDs my quad is flying much better than with David’s PIDs. But I can lower the derivative gradually and see how it goes.

And today I will give your latest PID’s:
P I D
Roll 22 10 17
Pitch 40 20 10
Yaw 35 16 13

another trial, which is, since I have installed SpeedyBee, not a big deal…

[Kevin_Erik]

Be aware that I’m using 6″ Props and 2550kv motors. If your using the default gear then you’ll need to bump things up some but at least it will get you in the same ball park.

[jstremmler]

Was flying Kevin’s PIDs today . We had a litte wind today, approximately 3 beaufort. My Biquad was flying terrible pitching up even more when releasing the sticks and flying against the wind. And with the lower P and I values it used much more time to level out with these PID values.

So tomorrow I will switch back to my own PID’s and will lower the D values for pitch a little. (going down in steps of 5 from 38 to 23)

[jihlein]

I’m curious, are you flying the pitch axis in rate or attitude mode? In calm conditions I can fly pitch in rate mode with only an occasional pitch up. If it’s windy, attitude mode is a must, and I’ve not observed pitch ups in attitude mode as of yet.

[jstremmler]

Did forget to tell that in the meantime I did install Betaflight 4.0.0.

Was flying in Angle mode in Betaflight. Horizon also works well and its just like with your quad in calm wind conditions I can fly it in Acro mode as well(but did install Acro Trainer mode for the biquad)

Btw one should not forget (like me) that in Betaflight we have to modify FF as well when we modify the derivative and want to have the same feeling at the sticks. So here is my calc for todays pitch D adjustments:

D FF

38 146
33 127
28 108
23 88.5

So I made a mistake. With Kevin’s PIDs I should have used FF=65 for roll and FF=38.5 for pitch. So I have to give his PID’s another chance.

[jstremmler]

Yesterday it was cold over here and wind was even stronger (4 beaufort).
So I was flying only 4 packs.

Changed pitch D to 33 first. For my opinion my bicopter was flying a little better than with D=38.
Next I changed to D=28 and the bicopter was significantly flying worse.
Changed back to D=33, but even with D=33 I obsereved some oszillations in the turns when changing flight direction from flying against to going with the wind, but only then.

Next I will gradually increase D for pitch in steps of 1 again and will slightly increase D for yaw in steps of 5. (actually my D yaw is 0, see above and therefore FF does not matter) So my next D and FF steps for yaw will be:

D FF
0 0 (this is what I was flying up to now)
5 19
10 38.5
15 58

P.S. Have to mention that I didn’t like the speed of my bicopter, especially when flying with Kevin’s PIDs. (lame duck) This might have been influenced by the OATs tilting of the servos and especially by my built construction moving them inwards when flying forwards. Therefore I have significantly increased the servo min and max values for the servos with the SpeedyBee configurator. Just by doing that I recognized that the SpeedyBee configurator didn’t have a servo menu so that I had to do that via CLI. As a result we can say that David’s positioning device cant be used for OATs.

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