Uneven output on CCW and CW motors (no props, on the bench)

ArduCopter Copter 4.5
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1

Heres my HW
FC: Pixhawk Cube Black
ESC: Tmotor 4-in-1 F55A Pro II
Motors: 400kV Sunnysky X4112S
Battery : Tattu 4500mAh 25C 6S
Weight of drone: 2.5kg

I am currently experiencing an issue where the CCW motors turn slower than the CW motors, and thus have a much lower thrust for those. I am looking at the RCout, and trying to ascertain what the problem is. I already ran initial tune parameters, checked the motor configuration so that each are turning in the right direction. I checked reversing both by switching the wires on the ESC, as well as in sw. I am soldering directly to the esc pads, not using bullet connectors. I have swapped the ESC, and saw the same results. I have swapped the motors and see the same results. They all operate on motor test.

Heres the latest log.

Heres what it looks like on startup

image
image422Ă—132 49 KB

Heres what RCout looks like

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image1146Ă—541 106 KB

2

Are the motors fully leveled? Or are they twisted?
Search this forum for “YAW imbalance”.

3

Would yaw imbalance still be an issue if im testing without rotors on the bench?

4

Testing without rotors on the bench produces invalid and false results. Don’t do that. It will just confuse you.

1 Like
5

I corrected the title, without props there is no thrust.

6

Oh i was told in the discord to take them off… will send log with props soon

7

No, do not do that.

Just use the mission planner motor test function to test the motors without the props.

8

Hmm ok. Ill lyk what i see

9

Hey! So I tested with motor test without the rotors. I did a test all motors at 50% and got 5070rpm for all motors. Then for 80% 8000. This is with a 23.93 cell voltage. I measured the rpm of each with a tachometer.

The expected rpm for 50% is 4786 based off thrust percentage * kv * battery voltage. Is that the correct calculation?

10

It depends on a lot of factors. Why do you want to know?

1 Like
11

I wanted to compare the expected rpm with what I was seeing to see if it should be good enough for when I do a flight test.

12

It is good enough for the first test flight if you configured it correctly.
And to test if you configured it correctly, there are better ways.

Have you read some posts on this forum on how to correctly configure your vehicle?

13

I have, but I only saw for before first test flight be sure to configure the motor directions and numbers correctly, and then do initial flight params. I also saw ESC calibration, but when I read the wiki page for that it said I didn’t have to since I was using DSHOT.

14

If you read the documentation and read some posts on the forum, and if the measurements are all the same for all 4 motors, you are ready to fly.

16

What prop size are you using?

17

The prop size im using is 15x5.5in

18

When I added the propellers I got this locking noise. Can this be caused by me attaching the propellers incorrectly? I only saw this behavior once I added the propellers.

@amilcarlucas

19

Ok so just did a test flight. It is unable to take off. When i put the props on, the rpm significantly decreased, and it appears that motor d is turning slower than the others (2000rpm at 80% throttle). The battery is at 24.8V. The props im using are 15x5.5in which are recommended by the motor vendor.

Any ideas?

20

Have you used ecalc multirotor?

Do all 4 motors work correctly in mission planner’s motor test?

Hoe are you measuring RPM?

It’s quite dangerous to measure rpm on a flying quadcopter without telemetry.

21

400 kV at 25 V and 15 inch and 2.5 kg is more than enough to fly… However, maybe your battery is not up to the task? The only reason for the RPM drop with props is that you are not getting the correct voltage. It could be battery connector, it could be low quality battery. 25C is indicator of the lowest power battery. You need around 10 A to hover, so check logs for current/voltage, or even look at the OSD to check if your voltage drops when you apply power.

Unless of course you inverted motor numbers or something like this…

Also, low kv motors may have problems with timing (screeching noise when accelerating the motor is one indicator of that), and you may have to disable ESC low RPM protection, for that you need to enter the ESC configurator. But before you start playing with that, try more obvious issues.