New PixHawk 6c Throttle issues

[mandoman (Tom Evans)]

I’ve tried this post before but I don’t think I explained the symptoms clearly.

I have my Tarot 650 flying well with my original HB Pixhawk 6c. Throttle response was nice and progressive allowing for smooth liftoffs, hover and flight. Unfortunately this original 6c suddenly failed (!) losing the FMU side altogether!!

I order a replacement HB 6c and now have it installed in the same setup as the original. However for whatever reason the output from throttle inputs is frightening different and I’m really stuck trying to understand.

When I raise the throttle nothing much happens until about mid-throttle. At that point the motors all come alive but not high enough to takeoff (thank goodness). Moving the throttle still higher I suddenly reach essentially full throttle and if not tethered the quad would uncontrollably take off with no possibility to achieving anything like an altitude hold condition.

Since I’m using the exact same parameters as with the previous (original) 6c I’m truly at a loss.

If anyone could give a little guidance about what to do about this situation I’d be eternally grateful. As it is right now i”m absolutely stumped and dead in the water.

TOM

[dkemxr (Dave)]

Post a link to a .bin flight log of the take-off attempt.

[amilcarlucas]

Looks like the classic “test a closed loop system in a open loop way and hope it does not notice it”.

That test is invalid and the results expected. But do post a .bin file.

[Juergen-Fahlbusch]

@mandoman

Since I’m using the exact same parameters as with the previous (original) 6c I’m truly at a loss.

Did you copy really all parameters from the old to the new FC? How you did this?
Some parameters, all calibration and some tuning parameters are HW dependent and need to be readjusted also if the module is in principle the same.

[amilcarlucas]

@mandoman You will be a lot better off using the AMC software to import the settings from the old FC into the new FC while guiding you though the process of calibrating the new FC parameters.

[mandoman (Tom Evans)]

I did it by hand “one by one”!

[mandoman (Tom Evans)]

Thanks for your reply!

I have experience (all BAD!!) with AMC. It simply has never done anything useful for me. It just produce a bunch of contradictory setting – a disastrous waste of time.

I’d really like to hear if you have anything to offer about the peculiar throttle response issue I’m seeing. Thanks

Tom

[mandoman (Tom Evans)]

I’m sorry I’m just not smart enough to decode your response :-(..

Thanks anyway

TOM

[Yuri_Rage]

Unless you share a log or, at a bare minimum, some saved parameters, we really can’t diagnose anything. It’s highly likely you flubbed the config, but that’s just speculating.

[amilcarlucas]

@mandoman

It just produce a bunch of contradictory setting

If you enter incorrect data it will produce contradictory settings.

And If you do not understand that some parameters require different values depending on the tuning step you are in, you might perceive that as contradictory settings, when in reality that is the correct way to do it.

Anyway, give concrete examples and I will help you understand, or fix the issue if there is one.

Post a .bin file or even better use the “Zip Vehicle for Forum help” button and post the resulting zip file

[dkemxr (Dave)]

@mandoman

I’m sorry I’m just not smart enough to decode your response

Not hard to decode posting a link to a .bin log file.

[amilcarlucas]

Here are some threads explaining it:

Uneven motors output on take-off

yes, the situation being open control loop: “no props” and/or “tied down”. The methodic configurator documentation explicitly tells you to not do this. It adds NO benefit, nor valid information. If you had read it, you would have known.

Motors do not spin the way I expected (no props on the benchtop)

Is this related to the EKF expecting the copter to tilt/move according to the inputs but it actually doesn’t? I also have some sort of issue related to motors where I can go to the full RPM of something like 11200 using motor test but when I put my RC throttle to 100%, the max RPM the motors reach is about 7400. Don’t know if this will happen in flight. Broke a prop and waiting for a new one

problema en velocidades de esc´s

If you are trying to do some sort of test on the ground, it is invalid. There are no conclusions to be drawn via open loop testing like that.

Motors do not spin the way I expected (no props on the benchtop)

Open loop actually means there’s no feedback. The system may or may not respond as required but there’s no feedback to be fed into some sort of controller logic, right?

How to make the same PWM signal on all engines?

Yes, it was on the bench with unmounted props. I don’t have a connection with ground station yet except over USB. Do you need a log with this test when it is on the bench? I still could reproduce the issue even on the bench. Done. I disabled this two options. Anything yet should be disabled? [Screenshot from 2025-10-17 18-19-17] I noticed 500 files as threshold, so actual logs after rotation could be in any other files. I am erasing it now to improve navigation. Yes, the first version with…

Pwm And RPM Issue (Solved-There is no issue)

That is normal, because without props, you are testing a closed loop control system in an open-loop configuration. So it just behaves like that. Once you put props on it and let it fly, it closes the control loop and things start to work as expected.

Testing without props before first take off of a heavy lifting drone (MTOW 70kg)

That is normal, ALT_HOLD is a closed loop controller. You do not have props on and are not flying, hence the loop is open and is normal that the controller performs the way it does. Stop doing incorrect tests and you will stop getting incorrect results.

ESC RPM measurements not equal

You’re chasing ghosts. Testing open loop control on the ground does virtually nothing other than confirm that commands are sent and received. Per motor RPM should be similar during motor test of same throttle %, but depending on a ton of factors, may not be identical. ArduPilot’s attitude controller takes care of all of that during flight, so your concern is almost certainly a non-issue.

T Motor Calibration Issues

Without props? On the bench? That test produces meaningless results. Please do not test a closed system in a open-loop configuration. It will never work like you expect it to do.