Teslahed's Adventures with Open Pilot (CC3D)

[teslahed]

Well i';ve finally got around to giving Open Pilot (a CC3D kindly leant to me by Gary ) a go. So far i';ve managed 5 mins of flight time and half an hours worth of PID tuning, after the initial setup.

I used the setup ';wizard'; to do the basic config which was surprisingly easy. I haven';t had the chance to mess with a dji naza but i get the imperssion it';s not totally dissimilar to the software used on that. Nothing like multiwii at all - much easier for newbies to the hobby to get started with. It';s just a question of clicking through the boxes and picking sensible options.

I watched this video and had a look through the open pilot website;

https://vimeo.com/24073238#at=2
http://www.openpilot.org/

I';ve set my ESCs to turbo mode because they are all simonk';d.

So - PID tuning. This is the tricky part. I have a lot of experience PID tuning multiwii and can setup a new frame / controller in about 15 mins without much effort (now - took a while to get to that point), but i haven';t got a clue when it comes to Open Pilot.

I have so far concentrated my efforts on tuning RATE stabalisation (Inner Loop) P values (proportional) for Roll and Pitch. I have flight modes setup on a 3 way switch so i can swap between stabalise 1 and stabalise 2, and i';ve set stabalise 2 to RATE mode only.

I';ve upped P from the default value (30 in basic mode or .00300 in expert) all the way up to 80 (or 0.00800). Oscillations set in so i';ve backed off down to 70 (0.00700) which is seems happy with.

I';ve also set Rate Mode from 150 up to 190 to make the quadcopter more responsive in the air. Eventually i want to have this thing flipping and looping - i may need to up it some more.

So my questions are;

i.) For basic PID tuning is this method ok or am i missing anything obviously important?

ii.) Is putting Rate mode up to 190 the setting i want to alter in order to flip quickly?

iii.) Multiwii allows you to add expo in the PID settings to balance fast response against smooth flying, which i like. I can';t seem to see any expo settings in the open pilot ground station software - do i have to add expo on my transmitter with open pilot?

Any other hints or tips would be most welcome.

http://youtu.be/Q8dGXWkIKbc

Looking at the video it';s possible i need to put P down a little more, it';s not totally smooth.

[SimonS]

You';ve watched Part 1 So now watch Part 2 - PID tuning.

http://vimeo.com/openpilot/pid-tuning

[Hands0n]

An interesting new flight controller - that is some horsepower in the SoC I must say. Having sat through Part 2 - PID Tuning I';m none the wiser.  I';ve got PID, understand that okay. But the control and configuration paradigm is not making much sense to me.

But it seems to fly well.

Is this supposed to be taking on the MultiWii or more elaborate FCs like the Naza and APM?  I';d have thought with that processing power and memory size it would be the case. 

[teslahed]

Open pilot should provide stunt performance similar to multiwii but has a better and smoother auto-level and nicer ground station software.

I haven';t actually flown mine outdoors yet so it';s a bit early for me to say what i think from experience.

Having sat through Part 2 - PID Tuning I';m none the wiser.

I also found part 2 quite heavy going. I';m going to watch it again tomorrow morning and it will hopefully make more sense the second time around.

[proudhon]

I';m looking forward to hearing your thoughts on the CC3D when you get some more flight time.

With regard to tuning PID values:

Tuning rate mode first is a good start. On the TeslaQuad the first approach I tried was to set the I and D terms to 0 and increase P until oscillations occurred, then back off P 10-20%. Then I increased I until I had good angle hold, and then I increased D until the overshoot oscillations disappeared. I think this is more or less the recommended approach.It worked pretty well for line of site flying but I felt the quad was ';over tuned';. The P term was around .5 and the I term nearly double that. When I started flying FPV it became more apparent that the tuning really wasn';t quite right.

So I then tried a different approach with better results: I set the I and D terms to 0, and then adjusted the P term as low as possible. It';s a bit more subjective and difficult to describe, but there was a P value where the quad was just barely flyable - any lower and it was like stabilization wasn';t working. Then I increased the I term until I had reasonable angle hold, but I couldn';t get it quite as locked in as the first method I used. Then I increased the D term until the overshoot oscillations disappeared, but using this method they were much smaller anyway. See attached screen shot for the final PID values.

The second method resulted in a much lower P term, but the quad doesn';t seem to hold an angle quite as well as in rate mode. To get around this I fly in axis lock mode on all three axes. See the other attached screen shot for the stabilsation modes I have set up - I typically fly in the second mode. Leaving the defaults in attitude mode worked fine (if you use the I and D terms in the rate loop, you only tune the P term in the attitude loop. This is what worked for me, but I';m sure by playing around with it you will get it figured out in no time. Setting up the TxPID option helps tremendously for fast tuning if you haven';t done that already. I also found I had to introduce a little bit of deadband (1 - 2.5) on the input screen to stop the quad wondering around - this I think was due to pots that didn';t centre perfectly on my 9XR.

As for expo, the GCS only allows you to adjust the throttle curve. I think the OP wiki recommends that you don';t program expo on your TX, but I have done so previously with no adverse effects. I also setup dual rates on my TX. You can see my stick range and limits on the PID screenshot. Full stick angle (deg) is for attitude mode, and is the maximum angle the quad copter will hold with full stick input. The upper limit of these values is 255. Full stick rate (deg/s) is what is important for acro flying in rate (or axislock) mode. It represents the target rotation speed of the quad when the stick is fully deflected. 400 deg/s on pitch and roll is sufficient for acro flying, but I use dual rates (75%) to knock this down to 300 deg/s when I';m trying to fly a bit smoother. It is possible to go higher, and given your ability I guess you probably will. As for the full stick rate setting, I can';t remember what this does, but I think it relates to attitude mode.

Well, I  hope this is somewhat helpful! I also found the wiki pretty good, but I did read it about 5000 times when I was setting up and tuning my quad. Let me know if you have any questions.

Cheers

[teslahed]

Thanks for your detailed response - i';m going to read it again tomorrow but it';s already been very helpful

I watched part 2 - PID tuning again and it made a lot more sense the second time around.

I get the impression from what you';ve said that if i want to make the thing acrobatic enough to flip and controllable enough to fly at the same time, i will need to add expo on my transmitter. I would definitely use expo (only on the flight controller) if i was stunt flying multiwii in this way as i would need high rates to flip but at least a bit of expo to keep the thing controllable and smooth in flight. Dual rates also sounds like a good option.

[proudhon]

Not sure where I got the idea that expo on the TX is not advised, but it seems according to these posts that lots use it:

http://forums.openpilot.org/topic/19467-expo/
http://forums.openpilot.org/topic/10878-rate-mode-and-expo/

Cheers

[teslahed]

Just been test flying the open pilot CC3D outside for the first time;

http://youtu.be/bgJHgk8_Udw

I imagine it needs a lot more PID tuning but it';s already flying ok. Autolevel mode feels great but i am not totally happy with the acro performance. I need to up the rates and add EXPO to get it flipping properly and as well as that it doesn';t feel as ';locked in'; as multiwii does. But then i am practiced at PID tuning multiwii.

[nub]

well be interesting to know what u think about it and how it compares to the multiwii boards once u have it finally dialed in.

[SimonS]

I think that the default roll rate is only about 150/s. I';ve got mine at 360/s at the moment.

It';s under the advanced tab.

[teslahed]

i have just upped my rate settings. My PIDs are now as follows;



thanks Simon.