Verify motors are level to fix yaw bias

ArduCopter Copter 3.6
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In an earlier post: Hexa with Cube Black on 3.6.10 (and 3.6.8) spaz in loiter mode then restablizes

We were diagnosing the fact I did not tune my copter…

Well, I have fixed that problem and now have my eyes set on figuring out what is causing the mechanical yaw bias in my hex.

Using the mission planner motor test, I spun each motor with props on at 15% and with a camera and counted how many frames/ prop revolution. They all fell between 17-18 frames (at 240fps if anyone cares) so I (think) I have ruled out the possibility of one prop causing more drag than the rest, so now I need to figure out which motor is off balance.

Here are the pics of the motor arms and how they mount to the frame. They’ll show there will be difficulty in tweaking the angle just a few degrees to try to fix it.

https://drive.google.com/drive/folders/1tFI2uAFW08DRWABt0Yb60jdJePSz0m6X?usp=sharing

So finally the question is, how can I experimentally verify which motor is misbehaving so I can try to fix or replace it? Are there any pro-tips on how to make sure the motor surfaces are all planar on a big drone like this?

Thanks,
Asher

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@Asher can you explain what you mean by mechanical yaw bias? What is the observed behavior of the aircraft you are trying to correct?

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My strategy is usually to flip the drone upside down so that it is resting on its motors. Then you can measure the distance between the propeller tips and the floor on each motor. This will show you if a motor is twisted. If your motor arms have an upward tilt, you will need to turn the props so that they are perpendicular to the arm to get a valid measurement.

3 Likes
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Thanks @Anubis - I’ve been doing this the hard way for quite some time :slight_smile:

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wow, but so hard if you have a non-bending GPS mast. :roll_eyes: