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

I'd check that simonk has updated the firware to work with pancake motors, i know there used to be problems with motor stalls, and the escs going out of sync etc. Maybe fixed now though.

Great guide, a little scarey doing a "string tune" on a Hexa with over 8kgs of thrust though..........still have all my digits an took me 10 mins to fix the verticle blinds unfortunately :)

Its much worse when u have a hexa withh more than 18kg thrust and around 7,5 kg alltogether weight(with camera)...i dunno how to do it this way.... :-((

Just wanted to say thanks!!! Looking forward to more!

Regards,

John

Its not going well with my re-tuning after installing larger props. I’ve done Daves method many times now and it always gives me very large P values. It fly’s like that but not very well.

So I went back to my old settings, used with the smaller props, which originally worked with the bigger ones as well. After hovering in the barn for I few minutes I took it outside and it just went berserk and crashed. Broke a motor mount.

I am suspecting vibration may not be helping.

 

Just for info-

My motors are smooth without props. The props are in perfect balance. Put the two together and I get a drill on hammer action. The motor shafts and prop drivers are straight and the prop fits tight.

Cause-

When checking the prop tracking (stand a box or bottle next to the copter and turn the motors by hand so the blades almost touch it) I saw about 4mm difference on 2 props. I just held them bent for a few seconds and re-test. Surprisingly they do stay in the new position (APC anyway). After doing this there was almost no vibration.

 

Quick one about prop balancing. I too use tape or clear nail varnish, but put it on the TOP of the prop. Its the underside of the prop that's doing all the work, making this surface uneven with tape of blobs of stuff can actually make the vibrations worse.

 

The only times I've had props fail inflight it's been right at the hub, so I'd never try to remove material in this area to achieve balance.

 

My advice is to dynamically balance. Just attach one motor at a time to your chnl3 of your rx, hold it tight, spin it up, add a bit of tape to one side, if it gets less shky add more tape (or remove a bit) until things smooth out.

 

Once it's balanced you should get little or no shaking at any throttle setting.

 

I should also add this is another reason why i like using those cheapo prop adaptors that everyone hates. They may be flimsy, them may bend easily, but they show up any vibration much more than if you have you prop adaptor hard bolted to the motor housing. I always look down on them from above and from the side, if they move at all under throttle then either things aren't balanced, something is bent or the prop is not centred, balanced or tracking correctly. 

Dave how do you come to the conclusion that the bottom does most of the work when it is actually the top of the airfoil where the air travels further  than it does at the bottom of the prop and that causes the higher pressure above the prop to give the lift.?

Take for example on a jet airline where the top surface of the wing is the most critical to maintain a smooth shape and surface and the engines are mount at the bottom where its less critical. This is also evident when it lands and the wing expands and the top shape is given a bigger rounder surface area to give better lift at slower speed. The underside is a bit of a mess really when this takes place. Thats just my view and observation though and I could be wrong. I use nail polish and keep it smooth and never have any issues with it on the bottom side.

I was about to ask that. Perhaps its just naming confusion. I would call the ‘top’ the most curved side (low pressure side) and that is normally the side most affected by roughness, which can cause the flow to separate. You are very unlikely to get separation on the high pressure side.

Ahh the principles of flight, always a good one to pickle your head.

 

If we had higher pressure above the wings then we would be pushed down. In theory we have faster moving air above, due to the greater distance to travel, therefore it's lower pressure (think stretched out). However this is not the whole story, in fact it's a bit of a myth, flat sheets at an angle create lift. Also, isnt the lower surface facing the on-coming air more? I know my tape peels off the lower surface fast!

 

A bit of food for thought, there is so much more our very own DIYdrones site

 

http://www.newscientist.com/blogs/nstv/2012/01/physics-in-a-minute-h...

 

I gave this some thought the first time i got the tape out. I couldn't make my mind up, so tried it. I find it much easier to balance the prop from the top, I get to a state of none shaking quicker by adding bits of tape, they don't fly off and seem to work. I just had nothing but trouble underneath.

 

It may just have been the props i was using at the time, so i could be wrong. Why don't we try it? So get equal bits of tape each side of each prop, on top at the front, below at the rear!  

 

 

Sometimes a step on the top surface will trigger the flow to separate and sometimes it will trigger it to turn into turbulent flow and stick much better to the surface. It depends on airfoil and Reynolds number. If you like to experiment with that stuff try the excellent free program XFLR5 which runs XFOIL.

 

Will certainly avoid a stiff neck sticking the tape on top.

Turbulence delays flow separation.

Yep sorry my mistake and correct the higher pressure is generated at the bottom not the top. (long day at the grind yesterday) But even this happens with a flat sheet as it travels forward at an angle with the front edge up. The air is compressed on the underside and a slight vacuum is created on the top side. Although when I was a kid I use to think that the air pushing underneath lift the plate and I still think this has some relevance.  After all, do the same in a medium that doesn't compress like water and it works as well.

I prefer the nail polish to tap becasue its easier to put on the right amount or wipe it off if its to much. I find tap is so fiddly.

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