Motors jerk after arming the quad

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mirzahadi
Posts: 7
Joined: Thu Sep 11, 2014 3:12 am

Motors jerk after arming the quad

Post by mirzahadi »

Whenever I arm the motors, they seem to be in good stable spin but suddenly one hears one or two of the motors go up in throttle without me giving any command. They jerk in speed up and down. Sometimes the jerk is strong enough to turn the quadcopter over. I have already broken two sets of propellers. The transmitter control seems to go away as soon as the motors go haywire. The jerk sounds very similar to a car driver throttling the engine up and down.

I have checked all the wiring, prop directions; they are good. I have calibrated each motor's ESC individually so that is most probably not the issue. The Multiwii config GUI shows all the values as they are supposed to be. ACC and Gyro are calibrated right. Nothing is upside down. Throttle, yaw, roll and pitch values are close to 1500. They all go to about 1970 on high and 1030 on low.

Is this a problem of receiver and transmitter? Is there any interference caused by motor wires near the receiver antenna wires? I am using a Futaba T6EXAP 72 MHz transmitter. My receiver wire is very long and I am winding it around all the arms of the quadcopter like a spider's web.

Any ideas will be really appreciated. I have attached some pics if they help.

Specs:
Frame: F450
FC: Arduino pro mini
IMU: 10DOF GY-86
ESC: Emax 4 in 1
Motors: Emax XA2212 Brushless Motor 980KV
Props: 1045
Attachments
33.jpg
22.jpg
11.jpg

Arakon
Posts: 196
Joined: Thu Jul 17, 2014 2:22 pm

Re: Motors jerk after arming the quad

Post by Arakon »

Yeah.. Winding the antenna around like that is an awesome way to cause all kinds of havoc. You should seriously consider getting a 2.4ghz transmitter.

mirzahadi
Posts: 7
Joined: Thu Sep 11, 2014 3:12 am

Re: Motors jerk after arming the quad

Post by mirzahadi »

I can't. Don't have the resources or the means as of yet. How should I wind the wire?

Arakon
Posts: 196
Joined: Thu Jul 17, 2014 2:22 pm

Re: Motors jerk after arming the quad

Post by Arakon »

Preferably in a straight line.
Also, you absolutely have to cover the baro with foam to protect it from prop wash and light.. otherwise baro mode will go completely nuts.
Check if you have vibrations when the motors are running fast.

mirzahadi
Posts: 7
Joined: Thu Sep 11, 2014 3:12 am

Re: Motors jerk after arming the quad

Post by mirzahadi »

I have put the receiver wire in a straight line. It did not help.

Here is a video to show the condition. The video quality is not that great but it will give you a very good idea as to what is happening. Keep in mind that the quad is just armed and throttle is at the lowest position and I am not touching any stick.


waltr
Posts: 733
Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Motors jerk after arming the quad

Post by waltr »

While you are holding the quad as in the video connect the USB and open MWconfig.exe.
Check the values from the RX (sticks), do any twitch?
Watch the sensor graphs, are they smooth or noisy? do the glitch?

mirzahadi
Posts: 7
Joined: Thu Sep 11, 2014 3:12 am

Re: Motors jerk after arming the quad

Post by mirzahadi »

Here is the video from Multiwii GUI. The channel values are not very stable, especially after arming the quad. Try to watch the video in a bigger window on YouTube.



So what really is the problem? Transmitter? Receiver? Wire connections?

Noctaro
Posts: 280
Joined: Thu Sep 08, 2011 11:15 am
Contact:

Re: Motors jerk after arming the quad

Post by Noctaro »

Hi,
i do not really know what causes the problem but got a few hints:

-Try without props mounted, same behaviour?
-Place your gyro better centered on your frame.
-If possible use some soft material like earplugs to mount your fc to. (Reduce vibrations the FC is exposed to).
-Try to force your copter to failsafe mode (best without props) and watch its behaviour. Does it still twitch?
-When i used long antennas, i preferred to add some drinking straws where i put it in or wood sticks to wrap it around and let it face away from electronics AND PROPELLERS. :_D

Hope this helped a bit.

Greetz
Noc

mirzahadi
Posts: 7
Joined: Thu Sep 11, 2014 3:12 am

Re: Motors jerk after arming the quad

Post by mirzahadi »

Noctaro wrote:Try without props mounted, same behaviour?

Absolutely no twitch or jerk whatsoever without props! I pulled and tugged the receiver wire and other wire connections and it did not induce a jerk. Put the transmitter behind a cover, it remained the same.

So what is wrong with the props or their mounting?

nebbian
Posts: 67
Joined: Mon Jul 21, 2014 6:54 am

Re: Motors jerk after arming the quad

Post by nebbian »

You probably need to balance your props.

As others have said you can isolate the gyro board with foam earplugs or similar, remember to put some weight on it, the weight of the board itself is so light that any vibration will just go straight through to the sensors unless you have a weight attached to it as well.

You can also try mucking around with the low pass filter in Multiwii.

Good luck, these sorts of issues are tricky to sort out.

waltr
Posts: 733
Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Motors jerk after arming the quad

Post by waltr »

It could also be prop vibrations causing an intermittent connection between the RX and FC.

mirzahadi
Posts: 7
Joined: Thu Sep 11, 2014 3:12 am

Re: Motors jerk after arming the quad

Post by mirzahadi »

I have done a couple of things which seem to have significantly reduced the jerk in motors. It is still there but about 90% of it is gone.

I have put double layer of a thick electrical tape on top of the ESC on top of which my FC resides.
I have put the receiver antenna wire in a drinking straw which is keeping most of its length straight.
I have Shielded the FC with some cardboard.
I have put the receiver on the bottom of the arm instead of top.

I can fly now! But I still hear once or twice a motor twitching somewhere during flight.

Anyways, I still want to know what exactly was wrong. I want to make another Quad for a friend and I don't want to repeat any mistakes.

BTW, Gyro filter at 42Hz is on but I don't think Gyro was the problem in the first place.

Noctaro
Posts: 280
Joined: Thu Sep 08, 2011 11:15 am
Contact:

Re: Motors jerk after arming the quad

Post by Noctaro »

Hi again.
I am glad you now at least are able to fly :)

However, you may try to add an BEC for your flightcontroller to clean up your powersource. Or you may also try to add an capacitor to the powerline and ground of the ESC which supplies the flightcontrol. Be sure only one ESC is connected as power supply.(Depending to the voltage regulator used in your ESC´s BEC it may induce error or in worst case cause damage to your hardware)
Sometimes voltage drops cause weird things. (maybe the load of the motors with mounted propellers create these)
Btw. i like to place my ESCs on the booms of the copter, not in the center. It will reduce electromagnetic interferences to your FC and you get the nice cooling 8-) effect caused by your props. (Get them away from your reciever and flightcontroller as far as you can)

This is how i do it:
viewtopic.php?f=9&t=3201#p42147

Greetz
Noc

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