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.

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Hi Kevin,

Below is my vibration log at Z axis:

Is it good enough? 

since my quad still climb slowly at alt hold and loiter, even after increasing the THR_MID at my hover point as Richard Boyhan suggest.

Any clue?

When it starts to climb, does lowering the throttle stop the climb? It still seems as if your THR_MID is still to low. What value do you have for THR_MOD?

Hi Kevin,

I will have another look at the logs and do some extra flights.

Also will enable the inav logs.
If I'm not mistaken the alt baro and alt inav should match, if not too much vibration.

It is quite interesting to figure it all out but sometimes frustrating as well.
As I'm using a TBS like quad it's quite time consuming when changing setups (vibration reduction).
In a way it is all part of the game :-)
Still prefer this than out of the box and nothing else to configure.

The same thing was happening to my quad when I made it lighter (removed fpv gear, gopro and used smaller batt). It would go up and down in alt hold or loiter. I then put everything back on and alt hold an loiter were stable again. I could not figure out which settings to change to keep it stable when it was going up and down.

Hopefully this information can be of some help... Maybe trying adding weight to yours to see if it will be stable?

Here is the weight of my quad,

With no fpv gear and gopro: 1240grams with 3200mah 3s

With fpv gear and gopro: 1464grams

Hi kevin,

I just made another flight to collect some data.

The accel-z doesn't look good unfortunately.

Way too spiky.

As mentioned I also enabled the inav logs.

Alt hold is sometimes ok but now and then I have pulsing motors.

The quad rises slowly to a certain point, then slowly descends to the initial alt hold setting, same for loiter mode.

I also included my latest log file.
Any thoughts are welcome.

Attachments:
Did you recheck your zAccel values? I had the opposite happen when I doubled my battery and increased my weight altitude hold was all messed up. It turned out that I had a bent motor shaft.

To tune Alt Hold you should start by reducing the Accel P term keeping Accel_I 2xP. You should not need to tune the rate terms.

Hi,

I solved the accel-z vibes and althold is fine now.

Vibes went away by adding a smale plate suspended by O-rings and some Kyosho zeal tape in between the APM and the plate.

It just needs a little tweaking, will keep the comment of Leonard in mind.
What I saw yesterday during the test filght was that in althold it dipped a little when doing fast roll commands left to right and back. When I did it more slowly I did not see this behaviour, so maybe a little more ALT_P?

Loiter an RTL are fine too but also could use a touch of PID tuning.

Nice tuning weather here so I've been out on the field and emptied about 6 lipo's.

I've been tuning the loiter and RTL parameters.

Loiter is fine but sometimes it twitches a little and then starts off in a toilet bowl spin (sometimes quite violently)

The next time I switch to Loiter it is very calm.


For the RTL part...
This is working but if I'm about 30m for the home position and I switch to RTL it very quikly picks up speed, overshoot a little, slams into the brakes (heavy tilting) and goed into toilet bowl.

When I engage the RTL from a closer distance it works well.

Auto landing is working as well.

When it is in a smooth RTL, it loiters for about 5sec, slowly descends and after a couple of minor hops it settles down.


Any thoughts on what to verify?
Here are my parameter settings (TBS like frame, 1100KV motors, 900gr weight)

Thanks

I've just spent a couple of days trying to work out the same problem.

Flew beatifully in Stab, Alt hold was great, and I could get loiter in calm conditions almost rock solid (except for the MTK drift).

BUT 

If the Hex was disturbed it went into the 'toilet bowl' manoeuvre, which, if left unchecked would result in a crash.

I found the most response was from Rate Loiter, lowering the P to 2.4, halved D to 0.2 and I down to .05 although it could probably have stayed where it was.

I was also able to get Loiter Speed to 0.7

The Hex still wandered and was not as locked in as I would like.

The biggest difference was made by replacing the MTK GPS with the UBlox.

I can now throw it around in Loiter, let go the sticks and it just locks into place.

Although sometimes I notice it gets into a drift to the right, and will just keep drifting until I give a bit of stick correction which locks it into that spot. It looks like one of the relocation variables is not being reset properly when the sticks are released.

Hi Mike,

Thanks for the feedback.
Sounds indeed lilke the same issue.
I'm also using the MTK GPS with an APM1.
I will try to tweak the Rate Loiter settings like you suggested as soon as the weather is fine.
I lowerd the loiter rate values to P:4 but not enough it seems.

Can someone suggest the parameter to change so the throttle stick position is about the same in Stabilize as in Loiter?

After updating to the latest firmware, when I go to Loiter from Stabilize the quad takes off rather quickly up.  In Stabilize the throttle stick needs to be about mid point to hold an altitude about 5 meters.  The stick needs to be only about 10% up to get Loiter to that altitude.  This makes transitioning between modes problematic.

Second question, since I didn't save the parameters before I updated the firmware, is there any way to recover them from old flight logs?  Loiter also jitters around a great deal now while Stabilize flies well.  It would seem if I could recover those previous values I might just set the current parms to those and regain Loiter stability.

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