This is starting to drive me crazy :) ....................autotune crash

ahh ok, so I’m assuming autotune goes from, for example, 0 pwm to 2000 in one frame which is impossible to replicate manually no matter how fast you move the sticks, makes sense

You can’t desync a modern 32-bit ESC like you did on the old 8-bit SimonK. You won’t see the prop stutter with the naked eye anymore, and that screeching grounding to a halt.
All the modern ESCs, HW, T-M, BlHeli_32, Kiss and whatnot employ a trick. When the zero-crossing (that’s a pole step) doesn’t occur at the predicted moment they stop powering the motor, count and time the next few zero-crossings, then reappliy power with the measured timing. Now, depending on motor number of poles, this zero-crossing happens in a couple of degrees of rotation so the whole process described above takes probably half a motor revolution, or less. Human senses can’t detect a desync today.

But then you can experience an avalanche of desyncs. You can imagine a motor doing each half of a complete spin in-sync / de-sync when it cannot cope with the requested change in rpm. It will provide just half the thrust demanded. Also invisible to the naked eye, but extremely obvious to an accelerometer in the FC.

Now, I’ve recently built a 12S machine, with Alpha 60A HV ESCs and MN701 motors, but it’s sitting at a paltry 9 Kilos AUW, spinning 24 inch props. Sorry @Corrado_Steri, I didn’t download any logs off it, as it behaved OK, but I’ll have it back in a month or so when its owner comes for flight training.

There’s a fine balance between motor capabilities, prop size, prop pitch and load. Prop pitch, for instance, is an overlooked factor. Same diameter, lower pitch, will take your motor in a whole different rpm envelope with a different effort curve to provide the changes requested by the FC.

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Very instructive write, thank you very much.
At the moment it looks like my best shot at the problem would be a desync.
As for prop i am using 28 inch plastic foldables from t-motor. We used them in a smaller build (18 inches and they work really great). 28 inches plastic foldables are the ones advice on those motors from manufacturer, so nothing out of spec.

At this point i don’t know if i should test some blades a bit smaller and with less pitch or going to new esc directly.

I don’t know if it makes any difference but my flame escs are 2 years old and possibly have a pretty old firmware on them.

If your ESCs are two years old, it’s probably not just firmware, but hardware, as well. I went OMG inspecting the last set of HobbyWing 40A, finding STM32F3’s inside. Great move from HW, but undocumented.

If I were you, I’d look at those crazy Aussies doing 12S racers, and the ESCs they build.

Hi Cornel
I didn’t understand you reply from “I went OMG inspecting…” onwards. Are you saying the Hobbywing 40A is really good hardware or really bad hardware ?

I took a look at those APD esc but it looks like are more oriented to race and not to big motors like we use. No where i could find a configuration with 100 or 120 kv motor spinning 28" blades.

I think i’ll go with new Alpha from T-Motor and hope all will be good. Once i’ll do it i’ll report back so it’ll be useful for other that will go big like us.

Thanks for the great support

Very interesting, thanks for the info :slight_smile:

The Hobbywing 40a are known to be very good for lower kv/larger prop combos - they’re often what is recommended when people are having desync issues, but I’d guess they’re probably not big enough to swing this combo? I’d guess that these tmotor ESCs are rebadged hobbywing btw.

Before you go ordering new expensive ESCs without definite reason (hoping for the best isn’t a good technical design), have a look at this:

Very interesting thank you. I see will only be in 3.7 and at the moment i am a bit reluctant to fly dev on such a large machine, i think the easiest and fastest way for me is just get some alpha esc (wich are foc) and hope for the best.

Have you been able to find the cause fot the initial issue?

I am going to autotune a 25kg Octo with U8 Lite 100kV and 28" props soon and this thread makes me a bit nervous. :thinking:

There were a couple of issues with our distribution board that we had to solve and we changed Esc, using T-Motor Alpha now.

Still didn’t test fly it, but there is plenty of people using Ardupilot on big copters so i think it was something related to our setup.

regards,

Corrado

Have you tested the motors for sync issues? My U8 pro’s were really bad with most esc’s. The new U8II pros are flawless with the Alpha esc’s though.

I tested P80III on the bench with Flame Escs and i noticed no desync, but after reading the very interesting comment by ThePara, i doubt i could notice desync as it happens nowadays on the bench. So i moved forward and got new Alpha 80 HV Esc and installed them. Still have to test them because weather is not collaborating and i had to solve a little problem i had on my distribution board.
Hopefully will test fly it tomorrow and see if everything is ok. Will keep you posted.

Did a quick test today and it looks ok. I carried out only roll autotune because it was getting dark but apart from a bit of twitchiness it looks ok now. It didn’t do anything strange.

Alpha ESCs feel a lot different in the air compared to Flame ESCs.

I am updating the post for future reference to other people.

I carried out the complete autotune and it worked as expected no problems at all. I think my problem has been solved. In the end looked like it was a desync problem.

So in my case T-Motor P80III and T-Motor Flame 80HV is a NO-NO.

With Alpha 80HV everything looks good.

Big thank you goes to @ThePara for explaining how subtle is desyncing with modern motors and esc.

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It happened again today, in a lighter way but it did.

We rerun the roll autotune to see if it got any better and actually it did. Now i would say pids are ok.

As said after we did roll autotune again and landed and stored gain we took off in stabilize to feel how it changed.

All of a sudden it gave an uncommanded pitch and roll (can clearly see it towards the end of the flight at second 988), can clearly see motor 3 gets maxed out and 4 goes down. This time it didn’t end up in a crash, it only did that wobble and we regained control and landed.

It looks like a desync issue again on motor 3. We changed Escs already going from Tmotor Flame 80HV to Tmotor Alpha 80HV, situation got a lot better because with old Esc it couldn’t survive 10 seconds of autotune before desyncing. I really hoped it got solved but looks like it didn’t.
Funny thing is that, if i remember correctly, even on the old Escs the motor 3 and 4 where the ones acting strange.

Log:
https://mshelisrl-my.sharepoint.com/:u:/g/personal/davide_monti_mshelisrl_onmicrosoft_com/EbJw9Pvz6OdIujxHfp44tLgBXrpKSN4W-GyM_3KA4VLeVw?e=AidoQB

Unless you’re publicly sharing the information here about how to correct these issues, this is spam.

Wrote to you, thank you for your interest in the issue.

Corrado

Please detail the issues and fix.
If this is a known Issue, please put up the public solution

He is from a company producing ESCs so i guess he will try to help me out with one of their products, wich is fine with me if they really work. I would really like to find an esc that just simply works on big builds.

@proficnc do you have any news, by any chance, about the canbus implementation of Here2?

Corrado

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I understand that their ESC’s are very good, but if there is a specific way it should be used, this would be best discussed in the forums, not in PM

Here GPS on CAN is already supported, but let’s not go off topic here.