The arducopter tuning guide.

 

This guide was written at the time of the release of Arducopter 2.8.1 FW. It is a compilation of everything I have gathered from the experts in the field of flight controller tuning. It will help give you an understanding of how to tune any rotor based flight controller, but its specific to Arducopter and this firmware release.

I will update this as necessary, or if you can convince me any of it is incorrect just post below and I’ll update this text.

There is a summary/quick reference at the bottom, so once you’ve read this rather rambling explanation you won’t have to again, other than to check details :D

 

The background

Tuning your flight controller is essential for a perfect flight. Even a fully stock frame will fly better if you tune. The default params will be close, but your battery or motors might be performing differently, your air maybe ‘thinner’ compared to the developer that last published the default params, so you should tune.

What we are trying to achieve is control. We start to accomplish this by modifying the amount of P, I and D in our control loops. All three react to our stick inputs and the errors created by measurements from our sensors, and all three will help us fly better. If we do not have enough of any of the params the copter will not feel like it’s under control, it will wander about, not resist wind and be hard to fly. Too much of any of the params and the copter will seem to have a mind of its own. It will over-react. At best you will see it oscillate, very fast, not so fast or somewhere in between, depending on which parameter has been overclocked. At worst it will simple flip over on take-off or be very unpredictable in flight.

We need to find a balance. You can tune each param up individually, but one will have an effect on another. Therefore we must tune one, then another, then go back and see if we can retune the first one again, this is the balance.

And this is where we adjust those parameters – Mission planner config page:

 

Before you start:

  1. Charge all of your batteries, you are going to need them.
  2. Check you are using compatible ESC’s, motors etc, some combinations cause problems.
  3. Balance all of your props (in-situ preferably – adding bits of tape or nail varnish to one side of the prop until the motor and prop don’t shake at all under throttle.
  4. Do all the other sensible things like check everything over and calibrate your ESC’s , radio compass etc.
  5. Set your copter up as you will normally be flying it. If you tune it then add or remove weight, or change the CoG, you will have to tune it again. Use your normal flight batteries, a 4s tune will be different to a 3S tune. If you don’t want to risk your expensive camera, just substitute its mass with something less valuable, like a bean bag or kids toy.
  6. Be prepared to have the chopper in your hand if possible and throttled up (so gloves on, maybe a full face motorbike helmet – that sort of thing, this way you be able to tune quickly and accurately. If you simply can’t hold it in your hand, or a simple jig such as you will see in the videos below – i.e. it’s a gas heli copter/ mad octo then you will just have to do it the long way round – in flight. But read this guide anyway it will speed you right up! (PS helis are not currently supported in 2.8.1, watch this space.

 

So let’s start tuning

Everything you read below will be demonstrated in the tuning video further down, so you know what to look for, and at the bottom is a summary for quick reference. I think, however, it’s important to include as much information here as possible as anyone starting into this hobby will often find this process to be a bit of a black art.

I’ve found the quickest way to tune the arducopter is to start with rate_D, (but you simply can’t do this unless you can hold your beast in hand or in a jig as the copter won’t fly without any rate_P or I) so a more universal way to start, and actually a more informative way is to start with rate_P.

Since this is about learning for everyone, let’s do it that way. I’ll give a brief low-down on the ‘rate_D’ tune (or Dave C tune, as it’s become known) ‘ later. (BTW, that’s very flattering but I’m only relaying info from the real experts, but hey, if I’m gonna be famous, why not for doing something I love  :)) Anyway....

 

STEP ONE - Tuning rate_P

  1. Put your copter in ACRO mode,
  2. Turn rate_D and rate_I to ZERO.
  3. Set your stab_P to about ZERO, or if you decide to avoid the jig/hand tune and go for immediate in-flight tune set it to about 3.0 as the code is currently using the stab param in acro mode), a true acro mode would not use the stab_P parameter.
  4. Set a range of rate_P you would like to work with. I’d advise 0.050 or lower to 0.225 the first time you do this as, although you are unlikely to end up near either extreme, you will see what happens at, and beyond, the limits.  You will be able to reduce this range as you become more familiar with tuning.
  5. If you know how to do it, set a pot on your transmitter as channel 6 and use mission planner to set your limits, if you have telemetry this is a joy, if not you are going to be plugging and unplugging your usb quite a bit, it’s not that bad though, and defo worth it.
  6. OK, time to go, hold copter in hand above head, or place in jig. Throttle up to about hovering point. Wiggle your roll and pitch sticks. With rate_P about 0.075 (unless you have a monster powerful chopper) it will react slowly to your sticks, it will feel relaxed, lazy. If you tried to fly this you’d be chasing it about with your sticks, you’d probably crash if it was nose in, if you know what I mean.
  7. Slowly turn up rate_P with your pot, or in MP. Move the copter about with your hand and with the sticks as you do so, raise the throttle a bit, lower it a bit, add in more rate_P. It will start to feel and look much tighter in the air, throttle right up and flick your stick the copter should move fast, decisively but then stop quickly and smoothly. If it seems lazy you need more rate_P, if it starts to bounce when you move the sticks or tip the copter about then you have past your limit at this point.  Get to a point where you are happy, it feels tight but does not shake.
  8. Save this rate_P, value, our aim is now to increase it using another parameter – rate_D so on to step two

 

STEP TWO – Tuning rate_D

  1. You have found a nice rate_P value (or so you think), so leave that fixed for now. For example 0.110
  2. Set a range of rate_D from 0.000 to 0.025.
  3. Throttle up in hand with rate_D at 0.000, things should be as you left them at the end of step one.
  4. Now start turning up rate_D, again move the sticks, shake the beast about, you will notice that at a fairly precise point you start to see very fast oscillations. This is your maximum rate_D, I’d set it just under where you can induce these fast oscillations by moving the sticks fast of shaking a leg.
  5. Now you can go back to rate_P and tune that again, you should be able to increase it considerably!!! So to step three.

 

NOTE: once you have found your rate_D you can try something interesting - you will have to hold onto your bird for this obviously. Set rate_P to zero, then crank up your rate_D as you just have. You will discover that these fast oscillations occur at pretty much the same level of rate_D, no matter what you have set rate_P to. This is why I think it’s more than possible to start tuning rate_D then move on to P. But that’s a shortcut, and this is not what this guide is all about.

 

STEP THREE – Tuning rate_P even more

  1. You have your maximum rate_D set, now try increasing rate_P again.
  2. You should be able to add at least 30%, maybe more before you get the oscillations. It will react faster to stick movement, be difficult to move with your hand and just feel very solid in the air.

 

Congratulations, your copter should be flying better than it ever has done before.

 

STEP FOUR

  1. Using your ‘happy’ rate_P and rate_D values, start tuning rate_I. This is better done in-flight and will feature in part two of this guide. Basically just keep tuning it up until you notice a loss of ‘feel’. It will hold an angle better for you, unless it’s too high then things go sluggish and eventually oscillate slowly.

 

 

STEP FIVE - HEAD OUTSIDE!!!

 

For now set Stab_P  at 3.0 - 3.5, closer to 3.0 if you have a high power machine, just to get you flying in stab mode. Then spend your time tuning rate_I and stab_P.

 

If you find your set up immediately too harsh, back off on rate_P and rate_D by 10% each, and try a lower i-term, if it's still too harsh do that again!

 

All that’s left is to watch the video below so you can see what I’m describing and head outside for fine tuning. Oh, and await part two of the guide and amendments from any discussions raised, then we will have a proper tuning guide that will be integrated into the wiki advanced tuning guide  :D

Results for tuning in this video were

 

Rate_P 0.168

Rate_I  0.654

Rate_D 0.008

 

 

Oh and as promised, below is Part One of the Summary Guide. I aim this to be on one sheet of A4 and tell you everything you need know ‘in the field’.

Summary Guide

  1. Tune up just rate_P
  2. Tune up rate_D
  3. Tune up rate_P more
  4. Tune rate_I as best you can
  5. Take it outside with a stab_p of 3.0ish and tune rate_I and stab_p in flight, to your liking, maybe adjusting the other params too slightly, to get it just as you want it.

 

Summary of what you are looking for

RATE-P

Too much rate P will oscillate quickly, and cause to copter to sound angry under stick input, bouncing rather than smoothly following your inputs. It will also shake more at full throttle and under hard turning.

Not enough you will not feel like you have full control. It will feel sloppy and be very easy to over correct with your inputs. It will feel delayed.

Perfect is where it feels locked in, stiff in the air, but not shaky. (although if I’m sport flying I turn it up a bit for maximum ‘wang’ and just tolerate the slight oscillations)

RATE_I

Too much rate_I will oscillate if you get high enough (a much slower oscillation than a rate_P shake). But quite a long while before it oscillates it will have other detrimental effects on flight performance, like a sluggish feeling or a tendancy to flip over on take-off. This is why I suggest tuning this in flight rather than in your hand/jig.

Not enough will cause the copter to get pushed by a constant wind, then it will fight back using just P. It will not hold a very firm angle during forward flight and will need more correction. This will not be as smooth as it could be in either case.

The perfect amount will cause the copter to lean gracefully into a constant wind, but also allow you to set a lean angle and stay there as you fly about. As you dial rate_i in pay close attention to the feel of the copter, you are not looking to create oscillations here at all, you should notice a strange ‘feel’ long before this point.

 

RATE_D

Too much rate_D will oscillate very fast, you will see a twitch forming then a fast buzzing oscillation

Not enough rate_D will simply mean you can’t dial enough rate_P and so you will suffer the effects of having rate_P too low.

A perfect rate_D will help fight the wind and follow your sticks as its fast to react, but will also allow you to reach a maximum rate_P level for you frame, thus giving better control.

Tags: PID, guide, rate_D, rate_I, rate_P, tuning

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Replies to This Discussion

Hey DanRZ,

 

By default you should have more than CTUN runnig, Are you sure that you are only getting CTUN? ( Ia ssume you know that you can go down a line and the column headings change)

 

If not, this link lists the extra logs you can turn on in terminal

Datalogging

 

 

Hello, i have more datas on logs :

Logs enabled : ATTITUDE_MED GPS PM CTUN NTUN CMD MOTORS.

And on your link i can see the "RAW" type. I suppose it is that value that i need to add to my enable logs.

Thanks a lot, i already have seen see that but didn't remember the RAW type.

So i  will add the RAW type and see what i get.

Thanks again for this really helpful post and have good flights for 2013. ;)

Leonard.

I tried the reccomended values and it felt vague, verging on uncontrolable. Strangley when a gentle breeze went through it went bezerk.

I started from scratch on a jig with Daves guide and ended up with even higher rate-P =.23 rate D=.014.

It seems happy outside with these values but havent got round to rate I yet.

I am usind simon Ks ESC.

http://www.unmannedtechshop.co.uk/rc-gear/bl-motor-esc/30a-multi-ro...

I had it flying really nice with the smaller props with quite high values.

I think I was having trouble recognising what a high rate P does but when I tried a 'silly' high value .3 the woddle was there, but went at about .25.

Vince

 

Hi mate,

If that is where you got to then it should be fine. Don't be afraid to back the numbers off if you still feel you have good control though.

I wouldn't take the Stab_P up though, I would keep all of them set to 4.5.

Leonard

When should stab_p be touched ? 

Good question. I am not really sure to be honest because I haven't had to change it to get very good results.

If you do change it you should keep Roll, Pitch and Yaw Stab_P equal. This is because Stab_P acts in the earth frame and is translated to the body frame for the Rate loops.

This means that your Pitch Stab P will be commanding the Pitch Rate loop and the Yaw Rate Loop if you are rolled over by 45 degrees for example.

Sorry I can't answer this question better!

Its still not flying sweet and I am beginning to wonder about vibration.

When I first set up the quad with 12” props there was loads of shaking and it was difficult to tune. Checked the props on a balance and they all were worse than I had ever seen before and needed heaps sanding off the heavy blade. Supposed to be APC but looked cheap and tatty.

Anyway, the current symptoms of vibration and tuning difficulty are much the same as before except the new props are all perfect. Im not that happy with a 14” prop on a 3mm shaft but they look straight after my crash. There is some tracking error on some of the blades. The prop hub is only about 7mm diameter so its a big ask for the prop to go on perfectly flat.

The top of the motor had 4 threaded holes. I would be much happier mounting a prop driver on those so will try to get some, or make some.

 

At the start of this thread Dave C says something about balancing the prop and motor together. How?

 

 

Vince

 

The only time I really touch stab_p is if it flies well in acro, but it doens't feel right in stab.

 

If stab_p is too high you will get a slow oscillation after a stick input, if it's too low it will feel a little sluggish returning to level.

 

The really important ones to get right are the rate params. The lowest stabP ive ever used was 3.8 for a way over powered X8, the highest was 5.5 on a highly tuned, well balanced, stock ardu quad.

Hey Vince,

 

I am a hydrologist, although I specialise in hydrodynamics much of the same principles apply.

 

A few golden rules about props which don’t seem to be common practice in the hobby word;

-        Never ever ever ever drill out the centre of a prop to make it fit a specific shaft size, you will never get it accurate enough without seriously expensive machining equipment. This is one of the most important points I can emphasize, not matter how much balancing you do it will not matter if the prop is not exactly centre. To this point don’t buy cheap props, use spaces or put tape/heatshrink to make up the difference in shaft size, get a prop then buy a shaft mount that is exactly the internal diameter (it should be a tight fit) or vice versa.

-        When adjusting the balance of a prop you never add/remove material from the blade, always add/take weight from the hub, this is due to the blade having a very specific aerofoil and adding/removing material normally results in turbulence on the surface of the blade which can be much worse than being out of balance (less lift on one side of the prop), to this point you are unlikely to be accurate enough without a computer balancer to get this right anyways but if you are going to use a home balancer such as the common magnetic balancers add weight to the hub. In my opinion if the prop is not balanced when you get it don’t bother using it. There is a reason why some brands of props like Master Airscrew are so much more expensive and you will see the results in how balanced and free from “extra moulding crap” they are. When I put these props in the dynamic balancer at work I am amazed at how close they are to being perfect and my assumptions is they are putting through a cheaper dynamic balancer themselves after moulding.

-        Technically it is better to balance a prop on the motor and most decent motors are normally not too bad although they usually get out of balance pretty quick from dirt getting into them from use. You won’t be able to balance the motor with the core in it due to the magnets, they have to be done separately and you also have to hope the shaft hole is perfectly straight and the grub screws holding it in are not warping the alignment all of which is going slightly out in a motor worth less than $40 (making a motor with a shaft alignment that is “true” and a balanced magnet and hub assembly is a true art  as even the strength and consistency of the magnet comes into play and cost significant money to achieve due to the tolerances that are needed in manufacturing). Just buy decent motors and they will be close enough.

-        The shape of each prop also plays a big role especially in the leading edge. This is a tricky one as it is very hard to check without a very accurate laser to measure it with. The cheap and simple test to make a plaster mould of one of the blades leading edges, then when it is dry you give it the lightest of coatings of a dark spray paint (like one quick pass) so you when you turn the prop round and put the other blade into the mould and push down and add a little vibration you can see the light colour of the plaster mould through the dark paint. If this is not showing the entire length of the blade you know the blade is not the same shape.

 

Now, in saying all that in most cases it does not matter that much in the hobby world as the vibrations really don’t make that much of a difference, but when we are using sensitive electronics that will be affected by the vibrations unfortunately it does and the less vibrations we have the better.

 

I do have a question, how big are your motors that are spinning 14” props?  

 

It kinda sounds like you might be loading up your motors too much and as a result they can’t react correctly to the changes being asked of them by the APM meaning it won’t matter what settings you put it if this is the case.   If you are spinning such big props and the motors are up to the task I would say you don’t need high stab _p rates. My hexa is serious overpowered and I only need a stab_p of 2.9, at 4.5 it has all sorts of problems and one would assume that this is due to the amount of thrust being produce and the APM not being able to deal with how much change is caused by only a minutiae increase in thrust.

 

Very interesting.  The shattered piece of prop (left side of the image) is exactly where I added tape to achieve balance.  I replaced them with more expensive fiber props and those were perfectly balanced right out of the package.

Thanks for all the info but I think ships propellers are so different, most of those rules won’t work.

 

You will never balance a model prop by working on its hub, but removing material from there could be very dangerous. I normally try to balance by adding tape/paint to the underside but with these cr*p 12” ones that wasent enough, I had to also remove by sanding. It worked. They were vibration free and the copter was nice. I dont think minor shape changes to the underside of a model prop will make any difference at these low Reynolds numbers so will give the laser leading edge measurement a miss this time. My point was more about vibration even though the new bigger props were perfect. There is no vibration from the motors alone. I can understand with boat props, any mis-shape could lead to cavitation.

 

Drilling hubs? Sometimes no choice. Done it 100s of times, mostly on 2-stroke motors where any vibration is not as noticeable. Normally just 1mm bigger.

 

I am using these motors and they recommend 14x4.7 props.

http://www.fast-lad.co.uk/store/products_multicopter_motor_4008-530...

 

The 12” ones hovered at 14amps and the 14” ones at 13amps. That’s about 55W per motor – not stressed at all.

 BUT, being so big they will take time to react so perhaps that explains my higher than normal values.

 

Thanks for trying to help.

 

Have you tried using the SimonK firmware on your ESC's?  I believe that is meant to fix some of this problem...

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