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Old May 30, 2013, 11:40 AM
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Joined Feb 2013
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One quadcopter motor slower than others

Hello, I have built a quadcopter with the MultiWii PRO Flight Controller w/MTK GPS Module. I calibrated the ESC's and I did all the other calibrations I could think of, but my back left motor runs slower than the others at all times. I've attached screenshots. Shen I first power up, they spin evenly at 0 throttle, but when I increase throttle, they spin up evenly except for the back left. I tried flying and it flipped over and crashed. Is this a bad ESC or something?
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Old May 30, 2013, 03:31 PM
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United States, IA, Grimes
Joined Mar 2005
119 Posts
Swap it with another motor on your quad. If it still does the same thing in a different spot, it's probably the motor. If it spins up and the motor you swapped it with is now the slow one, it's probably the ESC.
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Old May 30, 2013, 05:13 PM
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Australia, QLD, Loganlea
Joined Feb 2012
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Coombs I've been looking at the same board set up. Is that the software you get with it or download? Is it easy to set up or do you need an engineering degree? I'm new into multirotors mate.
Try what wraith said too
Thanks
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Old Jun 04, 2013, 07:05 AM
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The firmware is MultiWii and the GUI in the screenshots is MultiWii GUI hosted here: http://code.google.com/p/mw-wingui/

Pretty easy to set up.

Quote:
Originally Posted by OzBlueDragon View Post
Coombs I've been looking at the same board set up. Is that the software you get with it or download? Is it easy to set up or do you need an engineering degree? I'm new into multirotors mate.
Try what wraith said too
Thanks
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Old Jun 04, 2013, 07:06 AM
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I swapped out all the motors and it does the same thing. I guess I'll try switching the ESC's around. I have new ones on the way from HobbyKing because I wanted ones I can flash with SimonK, so I'm replacing all of them. Hope it helps!!

Quote:
Originally Posted by wraith0078 View Post
Swap it with another motor on your quad. If it still does the same thing in a different spot, it's probably the motor. If it spins up and the motor you swapped it with is now the slow one, it's probably the ESC.
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Old Jun 04, 2013, 04:34 PM
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I also have a multiwii, and my rear left motor also lags behind the other three. The front left and rear right start at the same time, then the front right shortly after, but the rear left doesn't start until I give it 20% throttle. It has to be a software issue, but I can't find where to change this.
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Old Jun 04, 2013, 07:36 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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I'm new to this and have a question. Does the controller have any way to monitor the actual RPM of each motor? I think not, it is actually just varying the PWM rates for each motor to correct the reading from the sensors, right? So unless all the motors have the same Kv there is going to be a variation in the RPM from one motor to another.

And the actual Kv's of motors is seldom, if ever, the number of the Kv that they are advertised as having. Some of them can vary by hundreds of RPM from the advertised values. It you want to see examples of the variations, you can look up motors at flybrushless.com and, in many cases, see actual Kv of the motor tested:

http://www.flybrushless.com/search

To tell if the Kv listed on the test data pages is the advertised Kv or one that was measured during testing, look at the values under the Constants heading. If the have 0's there the Kv is the advertised Kv, if there are values for the constants the value seen is the actual Kv. The vlaues for a typical tested motor would look like this:

Constants
kV: 2800
Rm: 0.08
Io: 1.55

The numbers will often be rounded off to the nearest 50 or 100 RPM increment.

If you want to test your own motors, you can get a "raw" Kv reading by running the motor at full throttle without a prop on it and reading the RPM and voltage at the same moment in time. The RPM divided by the voltage is is the raw Kv. And that will be accurate to within one or two percent of the actual Kv.

When you have a data logger attached that will monitor RPM and voltage you can look at the full throttle data for a 5 second or so period of time and that will even out the variations and give you a better number.

So if you did that for all motors in a set, it might point out a motor with wide variation from the others.

@coombs,

What motors are you using?

Jack
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Old Jun 04, 2013, 08:56 PM
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I'm using 2830-11s, 1000KV. I've switched out the rear left motor for others, and even when the motors aren't attached the multiwii GUI shows the rear left as lagging significantly behind the other three. It seems pretty clear that this is a multiwii issue, but I'm not able to fix it by recalibrating the ESCs.
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Old Jun 06, 2013, 08:40 AM
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I also switched my motors out for a new set and the same happens. Also, if I rotate the motors, the same position always lags. I would rotate the speed controllers, but that would require some major disassembly. Guess I should try it though.

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Originally Posted by soulcopter View Post
I'm using 2830-11s, 1000KV. I've switched out the rear left motor for others, and even when the motors aren't attached the multiwii GUI shows the rear left as lagging significantly behind the other three. It seems pretty clear that this is a multiwii issue, but I'm not able to fix it by recalibrating the ESCs.
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Old Jun 14, 2013, 12:56 PM
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Well, I replaced all the motors with DT750's and replaced all the ESC's with HK 30A flashed with SimonK and the back-left motor still spins slower than the rest. Guess I'll take it outside and test it out again to see if it flips over. If it does, this flight controller is going in the garbage. I have a KK2 on the way right now, but it hasn't arrived yet.
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Old Aug 25, 2013, 06:20 PM
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same problem

Quote:
Originally Posted by coombs View Post
Well, I replaced all the motors with DT750's and replaced all the ESC's with HK 30A flashed with SimonK and the back-left motor still spins slower than the rest. Guess I'll take it outside and test it out again to see if it flips over. If it does, this flight controller is going in the garbage. I have a KK2 on the way right now, but it hasn't arrived yet.
Did you ever find a fix for this Coombs? I have the same problem with my multiwii.
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Old Aug 29, 2013, 07:31 PM
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Found the problem

So, I'm using the Spectrum Dx6i transmitter and found that in order to get my motors to balance I had to adjust my sub trim throttle to -100. Other minor adjustments had to be made through Travel Adj and PID settings.
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Old Aug 29, 2013, 07:37 PM
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Coombs would you might be from Kentucky?
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Old Dec 12, 2013, 10:02 PM
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Joined Feb 2011
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faster rpms on right front!?

I have the multiwii with the gps also and the front Right RPMs are faster when I throttle up but the same at 0 throttle. It sounds like I have the opposite problem.
Did anyone find out how to fix this? is it a sub trim thing or the board? I have changed the esc and motors and it has the same problem.
thanks
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Old Jan 13, 2014, 09:07 PM
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Joined Aug 2013
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Solved

Quote:
Originally Posted by mbe575s View Post
I have the multiwii with the gps also and the front Right RPMs are faster when I throttle up but the same at 0 throttle. It sounds like I have the opposite problem.
Did anyone find out how to fix this? is it a sub trim thing or the board? I have changed the esc and motors and it has the same problem.
thanks
There is a new DEV Version of the firmware that solved this for me.

.code.google.com/p/multiwii/downloads/detail?name=MultiWii_dev_2014_01_14__r1648.zip&can =2&q=
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