Initial config parameters

[cih79]

Hello guys.
I need your help with, I think, initial configuration parameters for my quadcopter.
First of all, let me give you some details about the configuration of my quad with problems:
• 4 X Roxxy 3535/16
• 4X ESC Hi Model 26v/40A (tested ok…allthough I didn’t heard many good things about HI Model)
• Arduino Pro mini, BMA180, ITG 3200, BMP085
• 2200 Gens Acc (for testing purposes…I will need to buy a bigger one in the future)
• Spektrum DX7s (only 4 chanels used…if everything is ok I will try to use the rest in the future)
• Multiwii 2.0 software, configured after reading the tutorials etc), quadx
This is my second quad. The first one is a bit heavy (motors Roxxy 4250, the whole thing is about 5 kg), and running Multiwii 1.7. It worked ok…all the motors were running smoothly and evenly, the liftoff was a bit tricky. I think the cause was the weight, also I couldn’t control it very well…but at least was stable and after liftoff it stabilized by itself….I think that is the way it should. I tried to use also a newer Multiwii version (at that time 1.9), but it was not that stable…although I made the same configuration from the GUI.
Ok…back to the problem. After configuring the parameters, in the GUI, when I was trying to increase the throttle, the output for 2 of the motors was increasing more than for the other 2. Oddly enough, this behavior was not consistent…I mean sometimes was like this, other times all the motors were reacting in the same way. Anyway…I thought that this can be automatically compensated by the software (the first quad, although it did kind of the same thing in the GUI, in the real flight was compensating very well after liftoff).
When I tried to fly, for the first time with the problem quad, it behaved like in the videos (I am attaching the YouTube links). If necessary, I will make also some screenshots with the Multiwii GUI so you guys can see the parameters I used.
http://www.youtube.com/watch?v=Y25i5aqYCN8
http://www.youtube.com/watch?v=ahCcIcJYVlM
http://www.youtube.com/watch?v=ktptpS3D7Gw
http://www.youtube.com/watch?v=PI4IHJEr9mc

Thank you in advance for your replies.
Cris

[bill516]

Put the screen shots up then we can see whats happening, saves having to ask questions. For a start I will say Gyro only mode, that is all sensors off except gyro which is on by default. Set r/c rate to about .6, trim motors at 50% using GUI to get equal rpms for all motors, you should be able to hover at that and adjust trims to get hands off hover.

[cih79]

First of all: thank you for your reply. I will do exactly what you sugested about the rc rate. I'm not sure what you mean by "trim motors at 50%...".
The first screenshot is the multiwii with ESCs not armed, the second screenshot is with throtle at 50% and ESCs armed.

[bill516]

Trim motors at 50%. Arm motors and throttle up to 50% check GUI motor rpms and use TX trims to get them all approx the same, look at your GUI rpm reading they are all different. If doing this with props on be very careful, as you will have to hold the copter in your hand. Once you have rpms balanced then test fly and use Tx trim to get hands off hover. All the check boxes need to be clear to do this, you dont want any sensors active other than gyro which is active by default. Once you have Tx trim adjusted dont touch them again unless you make changes to, your model.

'Your next step will be to trim in stable mode but we'll do that when you get hovering.

[cih79]

Ok, I'll do that (prob it will take a few days since I also have a job...and a kid).
Anyway...I trimed the TX before...I'll try to follow step by step your instructions, maybe it will work.
Thank you,
Cris

[AndyM]

Cih79, I had similar problems with initial setup and bill recommended lowering rc rate to .6, I did but felt it was still slightly too responsive in relation to my inexperience at flying so I reduced further to .5 which seems to work for me. Another thing I noticed recently is at the beginning I was frustrated that my quad wasn't as steady/controllable as videos I'd seen on YouTube but with every flight I notice it is more stable/controllable so in my case anyway it's apparent it was pilot experience and not the quad itself. I was running on 1.9 until recently upgrading firmware to 2.0 (stable version) at the weekend, had it flying as well as I could've hoped except for an issue with twitches when MAG was on so this morning tried calibrating MAG sensor, when I connected to GUI and hit start I forgot to click 'read' so all PID values were still at '0', I did mag cal and clicked 'write', didn't realise I'd just wiped all PID settings :/, after reflashing 2.0 firmware and still same problem it finally sunk in what'd happened. Thats what led me to this post as i needed find & re-enter the 2.0 PID values to which your picture above proved invaluable, so thanks. Bills advice got me from flipping over every time I tried lifting off to finally getting some airtime so I'm confident he can do the same here.

One last thing re your motors giving varying readings the new 2.0 firmware does auto ACC calibration, I'm not sure the ins and outs of it but that may be relate to what you're seeing

Andy

[cih79]

Hello guys.
I finally got some time to test your suggestions and it went quite well I might say…but I think I have a lot to learn. I am attaching 2 videos…sorry about the quality.
http://www.youtube.com/watch?v=bE3Wt0zZjEI
http://www.youtube.com/watch?v=lOMgASaB-Mk

I want to learn how to hover at fixed point…and I got a little scared when I saw the quadcopter drifting a bit, and I crashed it (no problem, nothing broken). So…for now I am not using stable mode…and I think I need to learn how to fly before using this.
What do you think? From the attached videos, can you suggest any other modifications to make it more stable (without stable mode)? As you may see, I really don’t have a “clean” takeoff, I mean the copter is leaning a bit forward (and, of course, I tried to trim the TX a bit, but I couldn’t eliminate this behavior)
Thank you,
Cris

[bill516]

That is looking good, I dont think you have a stability problem, you may be overreacting a bit with the the sticks but that will calm down with practice, you can always increase expo to tame the sticks for now. As for the take off it will vary depending on the surface you are taking off from, a nice level surface like concrete or tarmac will be the best, next would be bare earth, then grass. Its all to do with the down wash from the props, on concrete the prop wash should be the same all round so you should have equal lift on each motor, but we have to trim for flight so your motors might not be exactly matched at the point that your copter is lifting so it will pull to one side until you are airborne. What you have to do is expect that movement and counter-act it with some stick input, the more you do it the more you will do it without thinking till you take off level. Uneven ground or grass will make the prop wash swirl around affecting your lift but once you are out of that turbulent air then it will be much more stable.

When you are close to the ground you are in the area known as ground effect, this is where the air is more dense because of your down wash hitting the ground and coming back up to meet your down wash, dont know if you have noticed but when coming in to land you have to back off on the throttle to get through the ground effect then put throttle back on to slow your sink rate. I find it a bit more difficult to hover a multi-rotor in a single spot than a single head helicopter because I think its the props and the wash they create, as well as all the other factors we have to contend with, wind, turbulence, ground etc. Hovering is like trying to balance a marble on the top of a football, (not in the hole where the air valve is), the more you go to one side the faster it will try to fall off, but it is worth being able to do it if you have a limited area for landing or take off.

Stable mode is not a magic button, all it will do is keep your copter level and return it to level should some outside force move it from level i.e gust of wind or moving with stick input then letting go of the stick. Stable mode will mot keep you in a fixed position either you need GPS for that, what you are doing it the right thing for now, learn to control your copter.

You can always practice with a simulator, I know there are some multi-copter ones out there but not what they are. I used Helisim RC its made for 450 helis but its cheap (free) and it gets you used to moving the sticks to maintain a hover.

[cih79_1]

Hello guys.
Unfortunately I forgot my password and I can’t seem to be able to recover it…no worries, I created a new user here.
So, from the last time that I posted here, I made some improvements to my flight skills and also to the quad itself (made it lighter, more balanced):
http://www.youtube.com/watch?v=H10Go1la_no
http://www.youtube.com/watch?v=jnxpdo4cnBo
http://www.youtube.com/watch?v=_kTa9XKI ... ure=relmfu
http://www.youtube.com/watch?v=PKkHNWqe ... ure=relmfu
http://www.youtube.com/watch?v=mPJsfisx ... ure=relmfu
I still have a problem related to the stable mode. I followed all the instructions related to calibrating the stable mode (at least I think I did everything). After the quad takes off, I activate the stable mode, and slowly the quad drifts a little to the front-left side. After I am switching off the stable mode and I compensate from the sticks everything returns to normal acro mode.
What I am aiming for would be get a very stable platform for the camera, one that I could just get to a certain altitude, switch to stable mode and altitude hold, and then just take some pictures without touching the sticks. So I am trying to take it slow, step by step: first I did acro mode…now I am struggling with stable mode and altitude hold…
Do you have any advices for me regarding this?
Thank you,
Cris

[Th0rsten]

Hi Cris

Did you trim stable mode?

1. Land and disarm.
2. Give full Throttle and than trim with the other stick.

In the video, the quad flies very well - you build it the right way.

[bill516]

Hi Cris, that is looking very good, its not dancing around the sky like some vids I have seen. Stable mode is only to keep the copter level and to re level to copter after an input be that from a gust of wind or a stick input. Stable mode is is achieved through the dark art of PID tuning which in a nut shell means lots of reading on the subject and lots of tweaking and testing. Its what makes this copter so enjoyable and so frustrating at the same time, what works for dos not mean it will work for someone else. Altitude hold is something that is in progress at the moment, some guys are really getting to grips with it and I expect they will have some real success with it very soon. If you want to get your copter to stay in one place while you take pictures then you need to get GPS, it will give you the option of position hold which will keep you copter in the same place regardless of outside influences i.e. wind, but dont expect miracles. GPS is only as good as the equipment you buy some are better than others some are cheap and others expensive, again reading is the way to the answer. There is also the option of gyro stabilsed gimble to mount your camera but I have no knowledge of them so its a case of reading again.

[cih79_1]

Hi Th0rsten.
Thank you very much for your response.
Yes, at least I think I did it the right way: motors disable, throttle stick full, trim with the other stick. The only thing that I can think about is that I didn’t repeat that action more then 4-5 times (I understood that this is a repetitive action sometimes….maybe I’ll get it right…).
Also…do you have any advice regarding the pressure sensor?(I am using BMP085) The guys from a Romanian forum told me that this sensor is crap…that I should switch to MS561101BA. I am not saying that this is not right….but I am thinking that having bought 2 sensors would worth trying make them work…also I understand a lot of people are using the BMP with some degree of success. How should I setup the sensor to be accurate?
Thanks,
Cris

[cih79_1]

Bill516,
Thank you also for your answer.
Well, a year ago, when I started buying motors, ESC and making the multiwii controller, I was hoping to heave the same results as mikrocopter ( I was not prepared for the long way that was ahead of me). Now I am a bit stressed because every time when I look at someone’s flight, it seems so easy to do…and so close to what I was hoping for…and at the same time it seems that I am very far from this.
So…I understand. I still need to practice, to wait for the developers that are adding day by day new stuff, and maybe to improve my quad design.
Also, I have the same question for you: should I stick to BMP085 or just switch to another sensor? (BMP is very sensitive, and from what I was told, is not good)
Cris

[Th0rsten]

that I didn’t repeat that action more then 4-5 times

It can be up to 20 times and more.
I always do 5 times, test, do 5 times again, test, than 2 times back and so on.
Can't help you with other sensors - I'm only using Gyro and ACC.

[cih79_1]

Yes…it works! It was only 10 times...lucky me!
Apparently I had to insist a bit …now I have stable mode which is too stable…and very hard to control (I will modify the PID a little bit).
What about the pressure sensor? Do you have any advices for me?
Thank you,
Cris

[Th0rsten]

Try LEVEL PID 8.0 0.010 100
That's my setting.

Did you shield the BMA from light and wind?
http://www.youtube.com/watch?v=-dbLm7XM ... e=g-user-u

[cih79_1]

Yes, the BMA is well insulated with some foam (of course, it's not sealed in foam).
I will give it a try in a few days.
Thanks for the link.
Cris

[cih79_1]

Hello guys.
I build last night a new lighter frame. I was very pleased to fly this new quad...it stays longer in the air (I got 5 more minutes of flight time), and it behaves very well.
Now my quad is 1.8kg, and I would like to try to make it lighter by using carbon fiber instead of aluminum ( I didn't find until now a good price for square 10X10 mm carbon fiber rods, for the arms, and good 2mm carbon sheet for the central parts).
Also, I wanted to tell you that I tried stable mode...pretty good but still too stiff...I need to work on the PID.
Any of you guys tried GPS? What do you recommend that I should buy? (I would like to try to keep the quad hovering over a fixed location).
I am attaching some videos of the new quad frame, taken by my wife today:
http://www.youtube.com/watch?v=Fl0tWOOfaqg
http://www.youtube.com/watch?v=yQ1jZjY-M4w
http://www.youtube.com/watch?v=HKyL_CORW1E
http://www.youtube.com/watch?v=6BxaBB8mHSk
At the end there is a bit of a piloting error ...but everything was ok...nothing broken or bend.
Thank you,
Cris