Reference build KISS ESC problem

[leopold1]

I recently build a reference quad based on Afernan's AQ6 Quad monoblock-610 KISS ESCs.


I recently received a mail from him concerning the following problem

IMPORTANT NOTE. KISS ESCs are used here with PID control. This is under development yet. We´ve discovered that under certain frame configurations high coupling with control can happen inducing high vibrations (> 1g) making impossible to fly. If that happens it´s necessary to increase DRATE & SLOT params (up to a maximum of 100) and decrease Tilt Rate D

Meanwhile I noticed some strange vibrations. when I give about 40% thr without props mounted, the frame would start to shake. See video



But when I go a little bit higher at 50% it goes away.
The ACC levels are between 2 and 3 when hovering.

On the other hand, the quad flies great with 610 motor to motor.
Previously I left the whole length of the carbon tube which gave me a quad of 780 motor to motor.
It also flew good.

Is there any progress in the problem? What steps should I take besides decrease Tilt Rate D

[leopold1]

No news?

[leopold1]

Concerning the "DRATE & SLOT params".
Where can I change this?

[afernan]

Hi Leopold:

Sorry for the late answer; I´ve miss this post.

I´ve progressed in this KISS-AQ matter. Below a summary of experiences:
- KISS is a very good and quick ESC that uses "freewheeling". Those facts gives the best performances but also are the main problems to get correct working with AQ. I got it working very well (awesom well!) with several quads. For small quads (400-450mm) using X-motor (2208) with 8x4.5 porps it works very well with deffault PIDs. Also with hi- stiff quads (using alu short beams 20x20x1.5mm, 150mm length). This is because all resonances are well above propeller exitation (>200Hz vs 80Hz excitation).
- For the 630mm quad size, 16mm tube (my posted design) the frame natural frequency is below excitation, but its harmonics could not, and those can generate resonances with the help of KISS sensibility.
- I´ve made already 4xquads similar in size/desing (like my 630mm) using KISS & PID control and in some of them I get very good performances (ACC<1m/s2) and in others was impossible to fly (ACC>5m/s2). That means that this design is not reliable and is critical.
- Changing SLOT/DRATE doesn´t change significantly the behaviour. You can get some improvements. But you can enter in another worst problems. To change SLOT/DRATE you need to recompile each time
-Changing FTerm (slope of the aplication of the control parameters) doesn´t solve also the problem.

In summary:

- If you want to use my frame use for the moment ESC32V2.
- With very stiff frames you´ll reduce significantrly the vibrations onboard and you can have the chance to use KISS. I´ll post a couple of frames I´m testing just now.

The good thing is when KISS-PID is working properly (with low ACC levels and PID values close to deffaults) it´s the best performances I´ve seen, specially with strong wind that it´s rock solid in the air.

[leopold1]

Angel,

Thanks for the explination.
Meanwhile I have been flying with the setup and this is one of my logs doing a hover. What do you think.

[leopold1]

Can someone have a look to check that my ACC are acceptable?
And in case I change the KISS ESC's by ESC32 would this give me a great improvement?

[afernan]

@Leopold:

your ACC are too high. You have around 5m/s2 peak-to-peak and this is in the limit AQ can accept. This is due to the KISS use with AQ as I´ve explained before. You can reduce significantly that ACC values by tunning some parameters (see attached document) , but loosing performances and then it´s not worth (I´ve done already).

The effect of the legs it´s also very important (see page 22 of the document). Pls post a photo of your setup

With ESC32 you´ll get better performances in PID and much better in QUATOS, for sure.

Attached is a paper with a record of my experiences in vibrations. Some day I´ll publish in our documentation. For the moment is still in draft but I thing the contents can be of your interest.

Angel

[leopold1]

Concerning the vibration problems of the KISS esc's in conjunction with Angels reference quad, I decided to change the KISS esc's with ESC32.

So the major setup like motors, props and frame were exactly the same. Nevertheless the vibrations with ESC32 were even worse. Changing Pid's didn't really work.

Here are the logs:

KISS ESC PID


ESC32 PID


After this major rebuild, and despite I really like Afernan ref quad, I took the decision to leave the reference quad frame and put the KISS setup on the cheese plate.

Result were absolutely great, hense the logs:


I hope in the future that PID tuning will still be available and that the code really starts using the full potential of the KISS ESC's!

[afernan]

@Leopold:

congratulation for your mount. You got a frame with PID-KISS working great. You got low ACC levels (2m/s2) from your logs.

The question is that builds using KISS-PID are not reliable with "soft" frames. I´ve made several builts already with KISS-PID, (even ESC32-PIDs) that gives very good ACC levels and so an awesom quality of flight, and others with "identical" frames not at all (it seems that was your case with my ref. frame). This is an inherent problem of AQ board using PID control now (not the case with QUATOS).

To waranty good performances using KISS-PID or ESC32-PID you sould use a "rigid" frame like this (http://autoquad.org/wiki/wiki/building- ... 16mm-quad/). Ive verified it in 100% of cases: awesome perfo with KISS/ESC32 and PIDs, and also with QUATOS. This is because it has a real frequency decoupling between frame and control. Not the case in soft frames.

Using "soft" frames (most of them are) you could have strong frequency couplings (mainly with KISS) simply by having slight frame changes. I´ve had many bad experiences in that sense with cheese frames, Warthox or my frames. Not the case at all with "stiff frames": 100% success with any ESC choose, or PID/QUATOS

Could you pls attach some fotos here about your builds using my frame and cheese-plate to see differences? Thanks

Angel

[leopold1]

Here are some photos of my builds since january

First of the ref quad with KISS ESC's. I flew quite well but some vibrations:



Then I switched to ESC32 + PID so a major overhaul of the build was needed. Thus same frame, same HW but with even bigger vibrations:









Then I decided to build the Cheese plate version which works great with KISS ESC and PID control.









Sometimes it was frustrating to rebuild the frame each time and had to cut a lot of wires but finally I have a nice flying machine. In the progress I learned a lot concerning AQ.