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  1. #1

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    Motor chatter

    I am Flying a Freedom 3-D / AXI 2826/10 motor, Jeti Advance Plus 40 amp speed control, e-Tec battery 3s2p 3400 at 10c, prop is 12x8 and draws 35.4 amps. Problem: motor cuts off at about 2 minutes into flight. If I throttle back and then advance throttle the motor emits a very loud chatter. The speed control is rated at 40 amps, 41 for about 1 minute. I am beginning to think the battery is at fault. At 10c the battery should handle 34amps, so I'm pushing it by using a 12x8 prop, which explains the cutoff, but what is the cause of the motor chatter????

  2. #2
    Moderator Matt Kirsch's Avatar
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    RE: Motor chatter

    erdootz,

    When you do pulls on the Whattmeter, pay attention to the voltage as well as the total Amps. Your setup might draw 35.4 Amps, which doesn't seem all that bad on the surface, but if the voltage is dropping like a stone, it's a giant red flag telling you that you're so far beyond capacity that the batteries are in severe voltage depression.

    An AXi 2820/10 with a 12x8 prop will draw well over 40 Amps on a 3S LiPoly. The fact that you're only drawing 35 Amps tells me that it's definitely a voltage depression issue. I would bet in 30 seconds on the ground, the voltage will drop below 10 Volts.

    The chattering is the motor trying to start. All sensorless brushless motors (i.e. 99.9% of what's on the market today) chatter a little on startup. It's normal for a brief chatter, you may not even notice it, but constant chattering is a problem.

    I am certain the chattering is related to your battery issue, though. When the motor cuts out, and you reset the ESC, the pack doesn't have time to recover. It's still at low voltage and doesn't have any "punch" to run the motor, so the ESC can't get past the startup sequence.

  3. #3

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    RE: Motor chatter

    Matt,

    Couldn't erdootz simply reduce the size of his prop to 11x7.5 to reduce the max load or do a 3s2P? I'm having similar issues with another 3D plane fitted with an AXI 2814/ 11x4.7 and a Jeti30. I can run a single 2480 3s on this plane which does well, but it flys longer and recovers better with 2 of them (3s2p)

    I notice that I can't cruise this setup at half throttle for long (during hovers and slow stuff) and then punch it and expect it to be there 100%, but for the most part I've had no issues with power to get out of trouble. The designer of the plane that recommended this setup informs me that if I intend to spend most of my time at half throttle I should step down from the 11x4.7 and go for a 10x5. He admits it's a bit tamer but more appropriate for the kind of flying he's seen me doing.

    I've heard that the controllers have to work pretty hard to maintain middle throttle settings while loaded and the heat that caused under those conditions can cause a thermal cutoff to kick in.

    Can you shed any more light on this stuff? I'm pretty new to electric, but a quick study.

    Regards, Ted


  4. #4

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    RE: Motor chatter

    My AXI 2212/34 just started doing this same thing. Sometimes it just stutters and won't advance RPM when I throttle up. Then, if I drop the throttle and re-advance it runs up smoothly and keeps running smoothly through subsequent throttle cycles. If you watch the prop when this is happening it is bouncing forward and reverse until it actually starts rotating correctly or, in the worse case, shuts off. Strange.
    Team BJCraft

  5. #5
    Moderator Matt Kirsch's Avatar
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    RE: Motor chatter

    Well, he is doing a 3S2P, and it's obviously not enough... 3S3P would be an option, but it also increases the battery weight by 50%, which may not be desirable.

    He could easily reduce the size of the propeller too. This would be the more desirable course of action, because a 12x8 is pushing that motor just a little bit over the edge. An 11x8 for example, would bring things down into a more comfortable operating range for all the electronic components involved. That may not be desirable, either, due to the fact that a smaller prop means less power.

    It will be a judgement call on the part of erdootz whether he wants to go with a more capable battery or a less powerful setup.

    Ted, you're also hitting those cells up pretty hard from what you describe. It's one thing to hit the LVC after a reasonable flight, but if you're hitting it after a short time at full throttle, talking about "recovery" and such... It's really not good for the batteries or the pocketbook, if you know what I mean.

    shannah, a little twitch is okay. Excessive twitching is a sign of a problem. Does your ESC have adjustable timing (should be described in the instructions)? Set it for the "hard" or "advanced" setting. If that doesn't help, check your connections. If that doesn't help, consult with the manufacturer or vendor of the ESC and see if there are any known issues. In the past, I've had ESCs with burned out FETs that exhibited similar behaviour.

  6. #6

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    RE: Motor chatter

    Thanks Matt,

    I do get a reasonable flight (maybe 10 minutes on a 3s) before I notice these power issues and do an approach. I don't think the LVC limits are being reached with what I was refering to- it's heat shutting it off which I realize could be voltage drop via excessive demand on the battery. When this thing happens after 4-5 minutes, I land and check the battery voltage- I'm usually between 11.5 and 11 volts (+/- .2v), and the SC is quite warm to the touch and the battery is warm. But is this not normal?

    Today, I was out at a local field using a 3s doing slow passes, true harriers to hovers (my first attempts at this ), and a witnessed harrier landing (if I could have done a back flip...) without any issues at all. Things felt warm as usual when I checked, but it didn't seem overly so. I'm left thinking that it's my inexperience and throttle management. Maybe I'm getting better ....or today was an exceptionally good day?

  7. #7

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    RE: Motor chatter

    Thanks Ted for your remarks on my motor chatter problem. My last flight confirms you pinpointing the problem with the battery. If I don't fly aggressively I don't have the cutoff, and the subsequent chattering of the motor, because the battery is not over taxed. It has been suggested that I go to a smaller prop and I may have to do that, but before I do I was wondering if I switched to using NiCD or NiMH if I could get more draw on a battery, with less voltage drop and consequently no cutoff and no motor chatter, and still have acceptable performance??? Again, that may still be a tradeoff because those batteries are heavier which effects performance.

  8. #8

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    RE: Motor chatter

    Hi erdootz,
    I'm left thinking that not flying aggressively was my problem. Since my first reply to this thread I've heard that the ESCs have to work harder when loaded at partial throttle settings (something about how brushless ESCs work.......?) . I worked my plane pretty hard yesterday and kept the flight times relatively low (<10min) with the single 3s. I know that I can get a good 15minute flight with 2 in parallel 3s2p and not worry about anything. I agree with Matt that if I had..say a 3 in parallel (3s3p)..I would have a better setup for reducing voltage drop which would definately end the cut off issues but then I would pay for it with an increased flying weight which would reduce the fun factor.

    So, I still don't know all of what will solve the issues for me. But the pocket change will be getting pretty thin if I go through a battery. So......



    I have to make another one of those parallel adaptors. I made one when I started this project and it walked away from my transmitter box......I guess I should have painted it flourescent green


  9. #9

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    RE: Motor chatter

    Thanks Ted for your remarks on my motor chatter problem. My last flight confirms you pinpointing the problem with the battery. I did go to a smaller prop, from 12x8 to 11x8, and that did stop the chattering of the motor. If I don't fly aggressively I don't have the cutoff, and the subsequent chattering of the motor, because the battery has not been over taxed. However, I was wondering, if I switched from using the LiPo to using NiCD or NiMH of the same capacity, if I could get more draw on those batteries, with less voltage drop??? That will still be a tradeoff because the NiCD or NiMH batteries are heavier which effects performance but perhaps I could go back to using the 12x8 prop and make up for the lost performance I have using the 11x8 prop?????? Any thoughts??

  10. #10

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    RE: Motor chatter

    Hi Ted Shredz
    My last reply to you on motor chatter should have gone to Matt Kirsch for his solving of my motor chattering problem. Sorry for the mix-up, but feel free to make any comments on my substituting NiCd's or NiMH for the LiPo.


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