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Common Problems and Solutions with Mini Quads
#1
We often see the same problem over and over, to save time repeating the same answer, here is a compilation of issues, with cause and solution. Please let me know if there is a common problem you see people ask all the time, so we can add it to the list.

#1 - Motor twitching when not armed

Caused: When your quad is not armed, your FC would still send a signal to the ESC's, i.e. Min_command. Even at 1000 (the default value), it might still trigger the motors to run at extremely low RPM. This signal isn't high enough though (at 1000), so the motors only twitch, but do no spin.

Solution: Lower Min_Command by step of 10 until the motor stop twitching, Min_Command is at 1000 by default, and you would probably end up somewhere around 990-950.


#2 - Why does one of my motors get really really hot?

Solution: Check if your motor screws are too long and touching motor winding.

#3 - My quadcopter is acting odd (vibration, twitch, rpm raising, etc.) when it's armed, but still sitting on a level surface without propellers

Cause: Arming the quad in any mode - rate, level, etc. will engage the PID controller. The PID controller will attempt to stabilize but without propellers the behavior will be unpredictable - exhibiting many of the reported symptoms, most likely twitching, jerking, apparent increasing of throttle.

Diagnose: Check motor direction and order first. Make sure your quad arms and disarms correctly. Test that failsafe is configured (best failsafe is a quick disarm). Put some propellers on the craft (again check orientation) and try hovering in an open and safe area. Chances are the craft will fly fine, if so tuning and fun are next.

Solution: If craft still jerks or twitches, check for obvious mechanical problems - bent shafts or bells, motor mounts, esc solders. Next most likely cause is the gyro - some are very sensitive to vibrations (MPU6500), in these case soft mounting might help, or a better FC altogether. Many retailers sell rubber mounting screws now that are almost direct replacement to the plastic FC mounts. (http://www.getfpv.com/m3-anti-vibration-...-of-6.html) Anything beyond that I would not consider a common problem and best is to provide detailed description and ask for expert help.

* Credit to Jordan Marinov

#4 - My quad flips on take off

Diagnose and Solution:
  • Check if your board is rotated around yaw axis, and if so please set the correct yaw offset in the software
  • Check if the rotation of propellers are correctly
  • Check if the ESC signal leads are connected in the correct motor pins on the flight controller, and you didn't connect them the wrong order
#5 - Motor Stutters

This can be due to the following reasons:
  • Incompatible ESC protocol
  • Cold soldering point
  • A phase of the motor is broken
  • Motor screws are too long and touch the motor windings
  • Damaged motor
  • Incorrect motor timing is set, usually the manufacturer gives a suitable timing. Desync by wrong "Demag" setting in BLHeli , test a higher value.

#6 - When I arm my quad, the motors run faster and faster on the bench without propellers. What is wrong?

This is a normal behavior. In this case, the PID controller attempts to control the aircraft, but because there is no propellers so the quad isn't moving, so the motors are trying harder and harder to try to move it. Just put the props on and test fly!


#7 - bars are not moving in the receiver tab? No RX activity.
  • Receiver is connected incorrectly, eg soldered to the wrong pins, short circuit or provided wrong voltage
  • Clean / Beta / Raceflight is configured incorrectly


In most cases, Clean / Beta / Raceflight is not configured correctly . For example, the "Serial RX" option must be selected for a FrSky XSR in the Ports tab, and "S-Bus" in the "Receiver" menu in the "Receiver" menu. The servo travel (visible in the "Receiver" tab) must also be set correctly. 

#8 - Why does my cop drift when hovering?

1. TX sticks need trimming. Use the trim of your transmitter to make sure your sticks end points are 1000 and 2000, and centres at exactly 1500, if the value jumps around 1500, you can consider setting "deadband" for this axis.

2. If this is horizon or angle mode, your ACC might not have calibrated properly. Also it's possible to trim the ACC if that's necessary.
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[-] The following 3 users Like Oscar's post:
  • Jordan Marinov, BigglesFPV, juha_j
#2
A variation of this one is asked almost daily now around the forums and FB:

"My quadcopter is acting odd (vibration, twitch, rpm raising, etc.) when sitting on a desk, without propellers, armed"

Cause: Arming the quad in any mode - rate, level, etc. will engage the PID controller. The PID controller will attempt to stabilize but without propellers the behavior will be unpredictable - exhibiting many of the reported symptoms, most likely twitching, jerking, apparent increasing of throttle.

Diagnose: Check motor direction and order first. Make sure your quad arms and disarms correctly. Test that failsafe is configured (best failsafe is a quick disarm). Put some propellers on the craft (again check orientation) and try hovering in an open and safe area. Chances are the craft will fly fine, if so tuning and fun are next.

Solution: If craft still jerks or twitches, check for obvious mechanical problems - bent shafts or bells, motor mounts, esc solders. Next most likely cause is the gyro - some are very sensitive to vibrations (MPU6500), in these case soft mounting might help, or a better FC altogether. Many retailers sell rubber mounting screws now that are almost direct replacement to the plastic FC mounts. (http://www.getfpv.com/m3-anti-vibration-...-of-6.html) Anything beyond that I would not consider a common problem and best is to provide detailed description and ask for expert help.
The next build will be perfect! | Fleet and build info | YouTube Channel |
[-] The following 2 users Like Jordan Marinov's post:
  • campagnium, Oscar
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#3
Also every variant of Flight controller numbers the motor locations differently, so sometimes the best intentioned "advice" can completely lead you astray because someone's assumed you've got the same FC.

Everyone says "your PIDs are wrong", not one person can explain why they think they're wrong Smile
[-] The following 2 users Like Aaron's post:
  • unseen, campagnium
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#4
I totally agree on this PID-voodo-tendency. Seems to be a way of profiling oneself w some well-sounding terminology, without actually having to do any brain-work. To my humble experience, and I'm a noob, PIDs are @ the upper scale of a complex system of variables that all together should be checked first. I'd like to add one of them out of personal experience, though:
Anything that prevents the FC from getting "symmetrical" feedback from the motors is likely to jam up the system or its smoothness. Like, as already mentioned repeatedly by others, a faulty ESC. In my case, it didn't have to be "fried" or visually recogniseable, it just wasn't doing the same job as the others and it confused the FC.
I ran into an innerly crushed ball-bearing on a brand-new DYS racing edition motor as well: It would still run smoothly when turned by hand, but upon higher rpms, the vertical position of the shaft would alter "just a little", but obviously enough to dissociate the stator/bell-housing planes and alter response patterns of the motor. Took me a while to figure that out,
so check on every motor before you install it by giving a good pull at the shaft while trying to jiggle it laterally. If the tolerance of the lateral jiggle is markedly higher (..basically, if you can feel it, that's already enough), you might consider replacing it before venturing into endless diagnostic exploration..
Keep it up, everybody!
[-] The following 2 users Like campagnium's post:
  • Drone0fPrey, unseen
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#5
(23-Apr-2017, 09:06 AM)campagnium Wrote: I totally agree on this PID-voodo-tendency. Seems to be a way of profiling oneself w some well-sounding terminology, without actually having to do any brain-work. To my humble experience, and I'm a noob, PIDs are @ the upper scale of a complex system of variables that all together should be checked first. I'd like to add one of them out of personal experience, though:
Anything that prevents the FC from getting "symmetrical" feedback from the motors is likely to jam up the system or its smoothness. Like, as already mentioned repeatedly by others, a faulty ESC. In my case, it didn't have to be "fried" or visually recogniseable, it just wasn't doing the same job as the others and it confused the FC.
I ran into an innerly crushed ball-bearing on a brand-new DYS racing edition motor as well: It would still run smoothly when turned by hand, but upon higher rpms, the vertical position of the shaft would alter "just a little", but obviously enough to dissociate the stator/bell-housing planes and alter response patterns of the motor. Took me a while to figure that out,
so check on every motor before you install it by giving a good pull at the shaft while trying to jiggle it laterally. If the tolerance of the lateral jiggle is markedly higher (..basically, if you can feel it, that's already enough), you might consider replacing it before venturing into endless diagnostic exploration..
Keep it up, everybody!

Good tip. Ty Big Grin
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