Post crash re-build: Can't fly very unstable

[attachment=0]2014-07-19 12-44-08.log[/attachment]3DR quadcopter
880Kv AC2836-358 motors
ESC 20 Amp with SimonK
3DR uBlox GPS with Compass
APM Power Module

Last week I crashed due to low RC batteries and stupidity. The only visible damage was some nylon standoffs, and one motor. I took it apart and rebuilt it with a new motor. On my first power up, I could see there was another bad motor. It would spin during testing with no prop, but after adding the prop, it just jerked around. I replaced that motor and did another ESC calibration, as well as all the other calibrations.

On my first test flight in loiter mode, it comes off the ground and immediately starts pitching and rolling until crashing. I took the props off and re-seated them, re-calibrated everything, checked that the motor rotation and prop type was correct. My second flight attempt was just as bad.

My guess is another bad motor, or two, or bad ESCs. My problem is that I don’t know how to diagnose that problem by looking at the log data. I don’t want to blindly replace all the motors and ESC.

Could someone tell me where to look, and what to look for, or any other thought you might have as to the problem.

I think I have attached the log file that I downloaded off of the SD card, and converted to .log.
2014-07-19 12-44-08.log


Have you checked motor order?

It may also be useful to see a photo of your setup.

I checked the motor and esc setup, and everything is where is should be. I looked through the logs, and the only thing that stood out to me was a large (largeish) voltage drop, when I applied the throttle. I thought my battery might be bad, so I switched out the battery and tried again. no luck, but I did notice that motor #1 (right front), was not spinning up as soon as the others. I gave it enough throttle to spin the props, and watched the props as I applied the stick to pitch and roll. I could tell by the direction it wanted to flip over, that motor #1 wasn’t giving as much power as the others. My next course of action will be to order replacement ESCs.

I can’t find any where in the log that shows whats going on for each motor. Can someone guide me?

I would be happy to provide a picture, just let me know what views you are looking for.

The RCOU message contains the motor logs. They go absolutely nuts. If it were a simple case of one motor being weak it would be keeping that motor at maximum…

I’d just like to see an overall of the whole copter to see if I can spot anything. You could try using the motors test in the CLI to check motor order.

Also check the connections to that problem motor and ESC, of course.

here is a link to a video of my quad and an attempted flight. you can see how it just starts pitching and rolling as soon as it gets off the ground, and then crashes. Hope it help, I sacrificed another GPS mast to get this shot. :slight_smile:

I really think it is the ESC. The front left motor, motor #1, doesn’t start spinning with the other at min throttle. I did another ESC calibration, and then motor #1 started spinning before the others, and would not stop spinning after bringing the throttle back to 0. I just don’t know how to verify it with out replacing the ESC. I would like to see some indication of the problem in the logs.

I also set the throttle at idol speed, and then pushed the stick to the left and right, and up and down, to see if the quad would try to pitch and roll the correct way. It didn’t, but that could be because I have it set in super simple mode, and my compass was dangling by its wires by that time.

Here is a video of my quadcopter and it’s trial flight. You can see how it pitches and rolls and then flips and crashes.

I think I have found a problem, but I don’t know what could be causing it. One of the tests i preformed, was to give the quad a little throttle, hold it by its legs, and see how it reacts when I pitch it forwards, and roll it from left to right. I look at the RCOU values during the pitch and rolls, and they look very strange. In stabilize mode, when I pitch the quad forward, I would expect motors #2&#4 on the back to decrease and motors #1 & 3 on the front to increase. Same idea for the roll… the motors on the side of the roll to increase while the other two decrease. However, that is not what I got. below is an summery of the data.

70deg Pitch forward
100% 50%

50% 0%

80deg Roll Left
50% 0%

100% 50%

80deg Roll Right
50% 100%

0% 50%

This out put looks like it would flip no matter what…which it does.
Any ideas as to a cause?


I cleaned the SD card and reloaded the firmware.
I took the props off, sat it on a table and armed the motors
I watched the telemetry data on the status tab of the Mission Planner
I watched ch1out, ch2out, ch3out, and ch4out as I pitched the quad forward.
The signals out of the Pixhawk to the motors look as I indicated in the above post.
This, I believe, is completely wrong.

Can someone make sense of this? Does anyone have suggestions for something to try?


A friend of mine has an Iris from 3DR, so I tested the RCOU (motor out), during a pitch and roll in stability mode. The numbers looked exactly like I thought they should. The attached picture shows the %.

When pitched forward the front motors get more power and the back get less. It’s the same for the Roll. When rolled to the left the left motors get more power and the right get less.

This further verifies that something is screwed up on my quad. After thinking about it overnight, and looking at the motor percentages again, it looks as if my quad is setup as a + configuration instead of an X configuration. This would make the data make preface sense. The problem is I have gone through the setup at least three times, once completely re-installing the firmware.

POSSIBLE CAUSE: Quadcopter set in incorrect + configuration instead of correct X configuration.

FIX: ??? anyone??


HOLY COW, THAT’S IT!!! I found the parameter that sets the frame type, and mine, for some unknown reason, is set to 0. 0 = + (plus) type configuration. That parameter should be a 1 for X type configuration. I double checked and that is what my fiends iris’s is set as.

Time to check this out. fingers crossed.


Darn, missed that possibility. Good sleuthing.