Hi Guys,

Today I decided I had a minute to test the parameters of my last tuning setup, not long into the flight, I had a real hard roll/pitch of forward and left, ironically, I switched the log to included motors just before the flight.

Attached is the file is anyone has a moment to check it out. I've had a similar issue months ago where it did sort of the same thing, the front right motor seemed to have stopped and caused this type of crash, I thought it was the spring clip on the bottom of the motor shaft that had slipped off or out of it's groove causing the motor to slide off the stator in which losing power of course. I looked at the clips and all are in place this time.

Hope someone can shed some light on this. Motors are too large and draw alot of power, and with this type of failure, it doesn't leave a whole lot of confidence in the hex to allow it to fly longer and higher.

F550 hex,
flying in x formation,
Motor's 1350kv
ESC's Birdie 30amp.
APM 2.5 3.0.1 firmware.
before this mornings flight, I also added to my midhover throttle, from 300 to 330. The last thing was when I came back to my desk, my mission planner showed "fence breached" on the hud. not sure why being ch7 isn't connected to the receiver. I did however have geofence enabled, just not active with the radio since there was no ch7 hooked up from the receiver to the apm.

Curious, is there anyway to write an algorithm for the apm to recognize a motor failing, sectionalize (doubt that's a word) the area of the surrounding two motors to stabilize the copter and allow for a safer landing? I've seen a micro quad do it recently.. food for thought.
This was also posted on Ardupilot forum hoping for some light on this issue.

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Hi,

Well around 1110 there certainly is a sharp turn down and left, but only for very short time and only 0.93 meters high.

I don't know how the fence is supposed to behave  (never used it) but I don't think you can assume that removing an RC  connection will mean disabled by RC. It might as well mean enabled, or it might mean keep using the previous or default value of the RC channel. Only looking at the source will really tell.

If a motor fails, a well made hex controller should not need to detect anything specially. It will just see that the corner with the dead motor is dipping, and apply more throttle to the dead motor and also to a lesser extent to its 2 neighbors (indirectly, wia pitch and roll controls and output mixers). This should go on until the neighbor motors have enough thrust to level the copter again, all by the normal working of the controller (and the dead motor probably has enourmous amounts of throttle applied to it, all to no avail. ArduCopter did, the last time I looked, additionally compensate for a motor getting more than 100% throttle by subtracting the excess from that of the diagonally opposite motor).

A hex is controllable on 2 axes with a dead motor. This should of corse be prioritized as pitch and roll, given that you can emergency land well enough without yaw control.

Try tie a big brick to that copter and let it run one or two batteries down at lots of power. Do all motors run well?

Regards

Soren

Thanks Soren.

I'll have to try that soon.  Looking back on the video of when this first happened, It's the same left #3 motor that "stopped" running.  Still don't know why, but when I have some time to get back on it, I'm going to perform a hard run on the motors while having the copter tethered down.  See if maybe the speed control is shutting down or something... just doesn't make any sense.

Another thing, Does any one recommend a specific setup of motors and props for the hex? I'm at my wits end with flight being something like 5 to 8 minutes long... These motors draw quite a lot of current.  Battery is 11.1 4000mah.  Flight time should be a bit better, but not with these motors, they're 1350Kv running on 9x4.7 props.

Thinking of dropping the motors down to 850kv range and 12x4.7 props.. seems folks are having better results.

Soren, I think on the question about the APM detecting a failed motor/s and compensate, would the speed and reaction in doing so, quickly enough to avoid smacking into the ground before control is regained. In my cases, just a meter or two off the ground wasn't remotely enough. I'm sure with an abundance of altitude, most situations can regain control again to safely land.  I have the video if anyone want's to see the first time this motor fail occurred to see if they have any input on it.  Let me know and I'll post it.

oh yea, since this last event, one of my motors bearing aren't the happiest... Lovely. only going to cause more drag and more draw in current. great.

This weekend  I ran the motors while holding the copter down and couldn't get a failed motor.  So what I did tonight was demonstrate just how two motors react to throttle up.  Hope someone can shed some light on this nonsense.  Also while reprogramming each ESC, I ran the motors individually and each throttled up smoothly.  What could be causing this stutter? I tried disconnecting several ESC's to see if it was a lack power getting to those two problem ESC's, but the stutter didn't go away.

http://www.youtube.com/watch?v=Nc-adV4fvJ8&feature=youtu.be

I had an ah ha! moment today while at work this morning.  Realizing that the other motors in my video were accelerating after a motor stopped was because the system was compensating for the failed motor with the other two to equal out the thrust to land the bird safely.  ...  Well at least that part is figured out.  Still stuck on why one if not two motors will shut down, or in some cases, not even fire up properly.  It's always the same two.  Even after swapping esc's.  Oh yes... and I realized in my video I called the ESC an ECU... lol  I work with ECU's all day long because I program Audi's and VW's for performance.  Sorry for any confusion.

Thanks in advance.

Hi Chris...Clearly there is something going on with motor 3. At line 1096 the fun begins. The APM senses the start of the roll/pitch and commands motor 3 to increase speed. Concurrently with that the APM is requesting motor 4 to slow down, as it's the opposite motor. The problem is, motor 3 doesn't increase speed and the error just keeps increasing. So motor 3 isn't doing what the APM wants. The question is why?

The first place I'd look is the ESC for that motor. It could be a flaky ESC or something as simple as a poor connection. In your video, if I heard right, you said something about the ESCs being in "airplane mode". What did you mean by this?

In looking at those Birdie ESCs at Hobbyking I see a lot of problematic reviews. It could be that the ESCs timing are not well optimized for the type of motors you are running, hence the erratic operation shown in your video. And they don't use SimonK. The net result could be very inefficient operation which brings me to....

I  see you are using crazy amounts of power even at hover. Are your motors hot after flying? If so it could be a case of exceeding the motor's power rating, heating it up and temporarily weakening the magnets. What model motors are you using and what is their power rating?

A couple of other observations.....At one point your voltage under load drops to 9.34 volts. That's very low and you risk having an ESC hit a low voltage cutoff, especially ones like the Birdies which may not be very programmable. Also for some reason your throttle out is consistently lower than your throttle in. I'm not sure why that is, assuming your radio is calibrated properly. Typically they are pretty close in level hover conditions.

Sorry I can't offer anything beyond this. My hunch is that you have poor ESC timing or programming causing the motor stutter and a questionable #3 ESC or a bad connection on that power feed.

Hi Tom,

Thank you for the feedback.  I too agree about the timing, heat, and pretty much everything you said.  I've been searching on the timing, and unfortunately, these esc's are only airplane mode.  Not timing adjustments.  I did program the esc's, however, I'm limited to what is available like cell type and break.  Literally that's it.  I'm been thinking of going with turnigy esc's so that I can program the timing and smaller motors because when the bird  pulls way too much power so when it actually flies (very rare occasion), the flight time is truly not long enough to film any sort of long video. I have a Tarot 2d Gimbal with a GoPro Hero3 sitting on my desk because I simply do not trust the bird to put this on and watch it smack into the ground wastefully. 

I've done a full re-calibration on the radio.  As for "airplane mode', these esc's for whatever reason, the esc only has airplane mode.  Clearly not the esc's to be operating a multicopter.  Oh before I forget yet again, the motors I have are, NTM 2826-1350KV running on 9x4.5 props.  The motors have gotten hot while flying, another reason to why I don't like them.  I've been doing some reading (when I get the small window of time that is) about what motors and kv folks are using for the 550 hexacopter, seems most are around 800 to 950kv.  Seen some with even 1000kv and such.  But my idea is to lower the kv, raise the prop size to 11 or 12 ish.. to bring down the amp draw a bit to preserve flight time.  Again tho, lower kv but larger props pretty much puts me back large power draw again.

There's gotta be a fine balance that works nicely.  That or just double up on my batteries. Currently running, 11.1v 4000mah.  I have two, and had thoughts for the future, once I learned how to tune and fly the copter properly, I would add the second battery, re-tune, then have longer flight times.  Now seeing how much power this bird has... I've had to tone it down a bunch, which is nice because if I stuck with these motors, I'd have enough power for both batts and the gimbal system.  Meh... Just need to get it flying properly to earn some trust with it. 

Arducopter is new to me, being the method of tuning.  I'm used to helicopters and fix wing, both r/c and full size.  It's just these PID's.. man they're killer! hahaha  Until recently I found some info that finally allowed me to wrap my mind around what they do and how they work exactly. 

Could you touch on the throttle out portion.  As mentioned above, I've done a calibration many time. Maybe I'm missing something.  Also I don't have any trims setup on the bird.  I did when I was first starting out. Any ideas on what or where I should start with the lack of correlation between the throttle out and throttle in?

Oh another thing that came to mind, what's the best way to check the balance on these???  I've tried just holding it with my thumb.. it's not very accurate. lol.    I mean sure, it functions, yet I don't really think it's best to go off of my thumb.

Over the weekend, I about killed one of my batteries by accident because I ran it down to far when testing.  So far I've been able to bring the cell back to up... wasn't that far down.  Hopefully it holds. 

Tom, thank you for the help and insight.  Really looking forward to trusting this copter hands off watching it run some filming missions. Hopefully sooner than later. lol Been a year... seriously.

Those motors look generally OK. They can handle 227 watts on 3S and 302 watts on 4S. I think your KV value is a bit on the high side which means smaller, faster props, a more responsive aircraft and shorter flight times.

To really get your answers you need to spend some time on eCalc modeling your hex. I put in some guesses for your hex and was coming out with estimates of around 6 minute hover times. There wasn't a Turnigy NTM 2826-1350 motor in their drop down options so I used a Turnigy SK2826-11 1350. Should be close enough. Try different sized props and also look at using a 4S battery. You might be able to pull a few more minutes. It will strongly depend on your hex weight.

Lowering your KV to the 800-1000KV range could make a big difference when coupled with the right sized props. Again, eCalc will give you the answers to this.

Fundamentally I think your current problems stem from your ESCs and specifically there's something likely weak with your #3 ESC. An ESC running airplane timing is not a good match for a multicopter. Consider upgrading to ESCs with either SimonK or BLHeli firmware. They will play much more nicely with your motors.

I wouldn't worry about the PIDs much at this point. You have deeper issues. The Autotune that comes with 3.1 seems to do a very good job of getting the tuning in the ballpark.

I'm not sure what the difference between your throttle out and in means. I haven't seen that before. Usually your throttle out, which is set by the APM, closely matches your throttle in, which is commanded by you. The only difference I've seen is when the APM adds or subtracts temporary throttle for "angle boost" when the aircraft isn't level.

As for balance, you're probably doing it right. Know where the center of your hex is and pick it up by that point. It should be pretty much level around that point. For my quads and tri I just lift it up with a finger at that point and see how level it is.

Thanks Tom.  I've used Ecalc playing around with something close to my setup.  I'm thinking, smaller motors and new escs to begin if not cure this problem.  I've seen while reading alot on the simonK firmware, but haven't looked into it just yet. Wasn't sure if turnigy plush esc by them selves were enough, or if I would need to flash the eeprom with the simonk firmware. Do you recommend only going with simonk or blheli firmware over the stock turnigy plush firmware?  More so, is the bird going to benefit from these direct changes rather than use the stock firmware?

Another concern is if going with smaller motors and larger props, is with the added weight of the gimbal and camera going to be too much to lift and sustain decent flight time for filming.  That and I'll probably have to double up on batteries.

I'll have to look into the 4s idea... I've kicked it around a bit, but haven't put serious thought into it.  Figured it was a bit toooo much.  haha.

Will need to get a solid weight on my bird with all the variables to consider to put into ecalc for a better idea on how things will go.

Been thinking of using mission planner with x-plane to get used to the flight modes and such. But when looking around a bit, I didn't see that you can fly a quad, just the fix wing.  Kinda puts a bind in my plan.

Ironically, I was fooling with ecalc, and managed to get up to 10-15mins of flight time, yet I can't recall the combination of motors and such that I used.... lovely.  I need to get a weight on my bird and start again on ecalc. 

Autotune looks quite awesome, been reading along with the thread thats going right now and it's been great seeing the devs help out and get these birds up and flying properly.  Been wanting to try AT but, gotta wait until my bird is airworthy and functional. 

Wondering, I read somewhere about the motor compensation that occurs when a motors fails, someone asked about different pid's to help make the bird still flyable when that situation happens.  Is there any way of have two sets of pid's stored that can be accessed in a time like this?

Again, thank you for your help. Looking forward to flying again soon.

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