HELP! Strange Acceleration Jitters

[doug sisco]

Hi all, I've been flying my little flamewheel quad with the Naza M for about two months and overall I'm very happy with it. Lately though it's developed a problem where the throttle accelerates in a 'jittery' way.

The problem only occurs when ascending, and I've posted a short video to illustrate the problem. In the video I am in GPS mode (though this also occurs in ATI mode but not in manual mode) and I am ascending smoothly. While ascending, you can hear the motors 'jitter' so that the upward velocity is no longer smooth. The problem becomes worse at times and the quad will sometimes ascend much higher or even 'bounce' up and down as I try to keep the altitude constant.

I've played with all the gain settings and performed an 'advanced' calibration and nothing makes a difference.

It seems as though the z accelerometer is faulty. Any ideas?

 

[Motopreserve]

I would say that perhaps the ESCs were not working well together, but if it doesn't happen in Manual mode, I think that rules that out.

Was there anything that happened that preceded this happening? Crash? Off calibration? Etc?

 

[doug sisco]

Motopreserve, thanks for your willingness to help!

Yes, the problem does not occur in manual mode but is pretty easily reproducible in ATI and GPS modes.

Yes, I've had a couple of accidents but I'm convinced that this problem has been occurring since before then: once it throttled-up and I hit some branches and then came down hard enough to break an arm. It seems to only occur when I am already throttling up slightly- it's like the motors 'catch' and jerk upward, maybe a Z-accelerometer problem. I'm ready to send the Naza M back for repair but I'd like to exhaust all other possibilities first.

 

[Motopreserve]

Of course! That's what we are here for

Couple more quick questions: does it do it if you throttle up but move away at the same time - so that you're not moving directly up (in its own prop wash)?

Does it do it if you are higher in the air? Say from 30 feet to 40 feet instead of lower to the ground up to 10 feet.

 

[cootertwo]

Lot's of things come to mind, but if it "was" OK, and now is not, it must be something that happened recently. I'd start with doing all the calibrations over again. Like a first time setup. Then see what happens.

 

[Motopreserve]

+1. Always good to start with a good, known baseline.

 

[doug sisco]

Thanks again, guys, for the responses.

Here's some more info: I didn't want to mention it but the quad decided to take a dip in my little pond a couple of weeks ago. I immediately took apart everything electronic and blew out the components with a hair dryer. The next day I tested it and it worked ok. The thing is, I believe the reason it crashed into the (15'x10') pond was because of this same problem, so it's very intermittent.

Today I disassembled the Naza and found the barometer component. I set my Weller on 300 degrees and heated it for about two minutes. Then I blew it out again using the hair dryer (on low heat). I was very careful not to get any components too hot (I'm an EE in my real life). I also noticed a little wobble in two of the motor shafts so I replaced two of the props.

I flew it again and the problem was noticeably less pronounced. I can't say it's completely fixed because it's so intermittent.

I also ordered four new ESC's. Of course it doesn't really make sense that the ESCs are to blame since the quad does not wobble when it bounces upward. But what the heck, I can always use them for my next machine.

And to answer your questions: yes, I think the problem occurred at high altitude also.

I'm going to fly a couple more times tomorrow and see how it goes.

 

[Motopreserve]

Well, not mentioning the submarine routine you tried probably led us down the wrong path

If you have dried it out and seen improvement - keep at it I guess. Rice always seemed to absorb moisture in these situations.

If you had noticed a motor shaft bent (likely in a crash) then I'd try to replace those shaft or just replace the motors.

If you've taken a swim - I'd suggest testing everything thoroughly on the bench to see what's happening with each individual motor/ESC combo. Just fire them up individually (sans prop of course!) and put them through their paces.

 

[doug sisco]

Actually I am certain that this problem was occurring BEFORE the pond incident: it was jumping up and down and that's the reason it landed in the pond . Yesterday I velcro'd a 11 oz camera to the top and the problem was much more prevalent. Also, one of the motors got hotter than the others. I'm going to replace that motor and ESC today and see how it works.

 

[Motopreserve]

What throttle position are you hovering at???

 

[doug sisco]

I think I may have discovered the problem: one of the motor's shafts had become loose from the housing, and it was very intermittent. Today it flipped-over after a five minute flight. Fortunately I rarely fly more than a few feet off the ground and there was no other damage.

 

[Motopreserve]

I don't know much, but one thing I know for SURE is that performance will suffer from a motor shaft not being attached to the motor!

Glad you got it sorted out. New motor won't be much to fix.