T-Motor 40A -400MHz ESC Questions

[ramdmc]

Hey guys,

I have a peculiar problem and am trying to track down the cause of flight instability. I have a rather large Carbon Core X8 Octo powered by T-Motor 4014-330 through T-Motor T40A ESCs. Oh and turning 16" T-Motor Carbon props. Pixhawk flight controller too.

Initially when I took delivery from the builder, it flew horribly and we tracked the problem to a couple of things, first it was running the default PIDs and had not been tuned, the next thing I checked was that the ESCs all had different setting, 2 had braking on, different start modes, and timing was not consistent across all 8 ESCs.

Since then I've had the f/c professionally tuned, and the ESCs all programmed the same via a program card.

Settings are as follows:

Brake: Off
Battery Type: Ni-xx
Cut Off Type: Cut-Off
Cut Off Voltage: Low
Start Mode: Normal
Timing Mode: Middle
Governor Mode: Off

All ESCs were programmed to these settings and it flies much better but periodically especially in low wind conditions will over/under correct. I've checked the log files and it appears that the F/C is sending the message to the ESC to correct but it's just not executing it fast enough. Initially I suspected the larger props taking much longer to react but have witnessed X8s with much larger 27" props handle wind effortlessly.

Have I programmed the ESCs incorrectly? I was going to try and chase this problem down and see if I can correct with my next course of action would be to buy a different ESC.

Can anyone chime in? I'm pretty bummed and I am not getting any support from the vendor, according to him, it's flying as intended.

Thanks in advance
RC

 

[Pumpkinguy]

Just by listening to you talk it sounds like you are pretty sharp with this stuff. Why the heck did you hire a builder? lol

Were the esc's throttle calibrated to your radio?

 

[ramdmc]

Just by listening to you talk it sounds like you are pretty sharp with this stuff. Why the heck did you hire a builder? lol

Well that's a very good question and at the time I just needed it and could not find stock of the parts I needed. I was under a timeline but believe me, I am so regretting it

Were the esc's throttle calibrated to your radio?

Yes, that's one of the first things I did. You mean throttle range calibration right?

 

[ramdmc]

And you're in Toronto, awesome, I grew up in the High Park area. Settled in Peterborough.
Read you build thread last night, nice hex man, I was actually considering a Hexacrafter frame, quality product, very impressed.

 

[Bartman]

@ramdmc

approximately what throttle % is the heli hovering at? what is it's total weight?

my best performance has come from helicopters with the throttle around 60% when hovering. at that point the motors have excess power to maintain control and the props are working hard enough to keep the aircraft airborne without a huge surplus of lift that can be hard to keep under control for the flight controller.

if you're hovering at or below 50% i'd put on smaller props, retune the PID's and try it again.

here's a great video explaining PID's but I suggest you prepare large amounts of coffee to help make the magic happen

ignore that your software is different, the fundamentals behind PID's are universale.

 

[ramdmc]

approximately what throttle % is the heli hovering at? what is it's total weight?

It's hovering just over 5o, I'd say around 55%ish. Total weight is just over 7.0kg. Going to take it out tomorrow to test a few things and strap a 1kg ballast to see if that changes anything, weather permitting of course.

my best performance has come from helicopters with the throttle around 60% when hovering. at that point the motors have excess power to maintain control and the props are working hard enough to keep the aircraft airborne without a huge surplus of lift that can be hard to keep under control for the flight controller.

This is kind of what I'm suspecting but haven't been able to observe , I'm beginning to suspect it's over powered.

here's a great video explaining PID's but I suggest you prepare large amounts of coffee to help make the magic happen

ignore that your software is different, the fundamentals behind PID's are universale.

Thanks for the vid, I'll check it out. I know manually tuning a MR can be a labour of love. The pilot who tuned mine happens to be a f/c dev and seasoned pilot, I know first hand how long and tedious the process is and although I was present, I let the pro do the work.

I'm interested in knowing the details and understanding the process better so that I can become less reliant on others.

Many thanks Bart

 

[maxwelltub]

Is your ESCs set to Nicad? Thats going to give you all sort of other issues with your battery voltage levels. There should be a lipo setting unless I am missing something

 

[violetwolf]

The pilot who tuned mine happens to be a f/c dev and seasoned pilot, I know first hand how long and tedious the process is and although I was present, I let the pro do the work.

His name's not Robert by any chance...

And honestly I've never found the need to tune pid's with pix or APM. They fly pretty damned good on stock settings. I'll adjust Loiter and Alt Hold.. That's about it.

 

[Pumpkinguy]

And you're in Toronto, awesome, I grew up in the High Park area. Settled in Peterborough.
Read you build thread last night, nice hex man, I was actually considering a Hexacrafter frame, quality product, very impressed.

Isn't high park where all thw millionaires live

 

[Pumpkinguy]

Looking at tmotor data I can assure you, you are not overpowered @ 7kg.
I think the motor selection is probably bang on. 950 grams of thrust x 8, less 10% or so for coax efficiency loss.
No way you are over powered.

 

[ramdmc]

Is your ESCs set to Nicad? Thats going to give you all sort of other issues with your battery voltage levels. There should be a lipo setting unless I am missing something

This is intentional so the ESC does not shut off motor when low voltage failsafe is hit. Rather kill a lipo than have a multi fall out of the sky. I'm pretty good bout leaving 20% in the battery at the end of my flight.

 

[ramdmc]

His name's not Robert by any chance...

Meh, I'm not naming any names. But if you require assistance with Pix/APM, I know a guy

And honestly I've never found the need to tune pid's with pix or APM. They fly pretty damned good on stock settings. I'll adjust Loiter and Alt Hold.. That's about it.

That was my experience initially but the craft I took delivery of was not airworthy. I mean, was tuned so poorly it flipped over as I tried to lift off on the maiden, imagine my disappointment. I mean a monkey on meth could have built a better MR

 

[ramdmc]

Isn't high park where all thw millionaires live

Yes, live. as in right now. My parents sold our house back in the 90s for what they thought was a lot of money. Presently, there is absolutely no way I could ever afford the house I grew up in, not even close.

 

[ramdmc]

Looking at tmotor data I can assure you, you are not overpowered @ 7kg.
I think the motor selection is probably bang on. 950 grams of thrust x 8, less 10% or so for coax efficiency loss.
No way you are over powered.

That's what I found, this is why I suspect the ESCs. You should have seen the ESCs when I got them, no 2 had the same settings, was so bizarre. I'm going to try a few things, one change at a time and test so I can observe the outcome of each tweak. I'm looking forward to some time this weekend but looks like the weather will not cooperate. I have a 500 ac field as my back yard and the wind coming off the ridge where my home is creates some crazy vortexes.

 

[fltundra]

. I mean a monkey on meth could have built a better MR

That totally sucks! I wish more people would think to ask for local assistance on the forums then they do. I always willing to help anyone with their build/maiden flight. It's always nice to have an experienced person too look over everything, especially with a first build.

 

[ramdmc]

That totally sucks! I wish more people would think to ask for local assistance on the forums then they do. I always willing to help anyone with their build/maiden flight. It's always nice to have an experienced person too look over everything, especially with a first build.

I totally agree and have helped friends int he past. Prior to this X8 I built a few quads, even got a Disco pro flying smoothly on a pixhawk. I bought this X8 from a builder because of time constraints and didn't have time or energy to "fiddle" with a mapping build. Plus no one had anything in stock which is common in the spring. Should have learned from last year. Going to stock up in March before spring fever hits.

 

[Old Man]

Might want to consider December before all the dealers offload their inventory and manufacturers shut down for the Chinese New Year a month afterwards...

 

[Pumpkinguy]

That totally sucks! I wish more people would think to ask for local assistance on the forums then they do. I always willing to help anyone with their build/maiden flight. It's always nice to have an experienced person too look over everything, especially with a first build.

When I was building my first big rig I would have loved to have an experienced guy that local to me for peace of mind help setting up the fc and tx bit I gotta say this forum was a very close second to having a real person.

 

[violetwolf]

Do you have any photos of the machine you can post? Barring a proper setup I wonder about things like pendulum effect, FC mounting etc etc.

The Pixhawk likes to have some vibration isolation. With an amateur builder this may be another area that got overlooked.

Same with layout and balance. X8's tend to be a little more finicky due to a small wheelbase in proportion to weight.

 

[ramdmc]

Do you have any photos of the machine you can post? Barring a proper setup I wonder about things like pendulum effect, FC mounting etc etc.

I don't but I can take some. I think it was built fine, mechanically anyway. CC Cortexes come built by Cam in the UK, local builder just chooses the F/C and gimbal set up. Thing is this frame was engineered for a DJI F/C. The Pixhawk is mounted suspended over the PDB on o-rings, it's taut and able to transfer direction changes, etc but not sure it's the ideal set up and this is the only other potential "flaw" I have suspected. My 3DR friend who tuned it suppressed my suspicions however.

The Pixhawk likes to have some vibration isolation. With an amateur builder this may be another area that got overlooked.

The vibrations are quite good, although a tight fit, none are making it to the Pixhawk nor are they showing up in the logs.

Same with layout and balance. X8's tend to be a little more finicky due to a small wheelbase in proportion to weight.

I made sure to balance it on the x-y axis, it wears a 22k mAh lipo on the top with the gimbal underneath, we had tested it with a 1kg balast velcroed to the underside and even with 2 of these 2500gram 22k mAh lipos straped to the top. No dramatic change.

Don't get me wrong, it's 1 million% better after 3DR dev tuned it and quite "functional". It's just not giving me that confidence I get when flying a quad or a hex. These things are supposed to be rock stable in the wind, not the case. I've never had a crash but in the current state wouldn't fly it over people. Experience has taught me that something just isn't right.

I just wanted to see if anyone had an in depth knowledge of T-Motor ESC programming so I could verify the state of mine. I've flown another CC Cortex but was an AP rig using an A2 and flew very tight so I'm beginning to suspect the ESCs or the suitability of this frame for the Pixhawk F/C.

I want you all to know that I am sincerely grateful for you're selfless offers for assistance and intelligent suggestions, this is a knowledgeable and mature group, I'm honoured.

RC