CW motors a way hotter than CCW

Hardware Multirotors
1

Hi ALL!
I built my X quad entirely from cheap Aliexpress parts and it even flyes.
But, motors 3 and 4 becomes very hot after a few minutes of hovering when motors 1 and 2 stays barely warm.
I’ve already tried to swap motors, props and ESC’s and i even tried a different models of motors and ESC’s but the problem remains the same.
The only thing i didn’t try to reaplace is a frame and probably it causing the problems.

I read some topics about the similar problems and found that motors became hot because of misalignment,
which as i suggest is caused by crooked frame.

My question is how i can identify which motor or motors are misaligned?
Is it motors 1 and(or) 2 which stays cool but causing yaw, which requires the motors 3 and 4 to work harder?
Or it’s motors 3 and(or) 4 which have less thrust and therefore have to spin faster?

Please see the attached log, it clearly shows that motors 3 and 4 output is higher than 1 and 2 but looks like difference isn’t that much. http://rgho.st/6FRjsw2wk

My current setup:
Motors: GARTT ML 2212 920KV
ESCs : EMAX Formula 32 45A
Props : 1045 DJI-like
Frame: https://www.aliexpress.com/item/FPV-Quadrocopter-X500-500-Quadcopter-Frame-500mm-for-GoPro-Multicopter-TBS-DJI-Spider/32497216065.html?spm=a2g0s.9042311.0.0.27424c4djjbsCg
Pixhawk running the latest firmware V3.5.7

Thanks in advance!

2

I don’t think it can be estimated just on alignment/misalignment, it depends on what way they are misaligned (helping the yaw or counteracting the yaw).
The issue with a slightly crooked motor is that it can either aid or counteract the yaw authority of that motor, dependent on which way it is crooked. My guess is that the hot motors are crooked in a way that counteracts the yaw, but i’m not sure.

The easiest way to solve this problem is not aligning them level on purpose. U can use some rings under the motor or try to twist the arms slightly (with some heat). You could even try switching arms (left/right).

(on a traditional quad) You can align them so the propellers are higher at the nose and tail of the vehicle and lower on the left & right side. This helps yaw authority.

Also, that frame is not rigid, and that can also cause motors to heat up too. The frame also fits real DJI arms, those are stiffer and more likely to be straight. So you might not need a new frame, just new arms.

3

First off you need to setup the battery monitor and the low battery fail safe, and then you need to fully charge the battery.

According to the log the battery started out at 11.6645 volts. At the end of the flight battery voltage was 9.9 volts. A fully charged 3S LiPo is approximately 12.8 volts. Second, total current flow starts out at ~19 Amps. By the end of the flight total current flow is over 21 Amps. Total current consumed is 2960mAh.

So, what we need is a complete list of what you have including batteries. We also need to know how much the frame weighs without the battery, and how much each battery weighs, and how many batteries the aircraft carries in flight.

For the battery monitor calibration read this: http://ardupilot.org/copter/docs/common-power-module-configuration-in-mission-planner.html . Calibrate the battery monitor for voltage. To calibrate the battery monitor for current read this:

The basic process is you take a freshly charged battery, Power Monitor Calibrator.zip (6.2 KB)
make a flight of 5 minutes or so, land, disarm and unplug the battery.
Charge the battery and record the mAh charged. We will call this number “CHARGED_MAH”

Now take a look at the flight logs and find the total current used. We will call this number “LOGGED_MAH”.

Next look at the BATT_AMP_PERVOLT parameter and record that number (by default its something like 17…). We will call this number “OLD_AMP_PERVOLT”

So, let’s say LOGGED_MAH was 1300Mah, and CHARGED_MAH was 1500mAh, and OLD_AMP_PERVOLT was 17.

We can use this formula:

NEW_AMP_VOLT = (OLD_AMP_VOLT x CHARGED_MAH) / LOGGED_MAH

NEW_AMP_VOLT = (17 x 1500) / 1300
NEW_AMP_VOLT = 25,500 / 1300
NEW_AMP_VOLT = 19.61

Set BAT_AMP_VOLT to 19.61 and click “Write Params”

Take a fresh battery and make another 5 minute flight.

After one or two iterations you should be well within ± 200mAh…

I have attached a spreadsheet that will do the math for you…

Looking at RCOUT, I’m thinking the aircraft is not balanced properly. Motors 3 and 4 are pretty close, but motors 1 and 2 are “off”. Motor 1 is lifting more than Motor 2, so I’m guessing the aircraft is heavy towards Motor 2 (aft and left.). Ideally what you want is to have the frame balanced in roll and pitch.

4

I was thinking about that.
But, assuming that we do not know which motor is crooked, I will have to check 4 motors in at least 4 directions.
I was hoping that we could narrow down the number of trials and errors at least to one pair of motors.
I will start checking from the hottest motor number 3 and report back when i get some results.
Also, thanks for the idea about heating the frame arms, when i figure out (i hope) which motor causing the problems i can then bend that arm.
I feel that this is not an arm itself, but an arm to frame mount, the threaded holes on the frame also slightly misaligned:/

5

Only 2 sets of motors can be wrong in 1 direction or not wrong.
Either the hot motors are wrong in a way that they cancel out the torq generated by the prop. (This would be my first motors to check)
Or the cool motors are wrong in a way they aid the torq of the prop.

To check alignment, you can take 4 flat plates (wood) with a hole in it, and mount it as if it’s a propeller, making it easier to see the alignment.

6

Yes, i forgot about CG. Also very important.

7

Thank you for extended answer about the battery.
Actually it was a second flight, so the battery was discharged already.
Here is the first one: http://rgho.st/8f8ls4PZx
You probably noticed the crash at the end of the 2018-08-11 23-28-17 log, this was probably caused by “Low RPM Power Protect” feature of blheli_32 . Looks like when voltage get down to 9.9-9.7V ESCs started to limit the power supplied to the motors. I will check this soon.
But first i want to solve this motors heating problem, i think it may cause motor degradation and complete failure.

8

I’d start with balance. I’ve thought this through, and I was mistaken about the out of balance. Instead of being heavy aft and to the left, the aircraft would actually be heavy forward and to the right.

Think about this from the standpoint of thrust vectors. All of the motors should produce equal amounts of thrust that is perpendicular to the frame.

In your case Motor 1 is making more thrust than Motor 2 is, and Motors 3 and 4 are pretty much even. This is an indication the frame wants to roll and pitch towards Motor 1.

9

It has been some years since I dealt with this issue but it was fairly easy to rectify. If motors 3 & 4 are running hot on a quad then they are attempting to counteract an imbalance that is imparting a clockwise moment to your frame in flight. This could result from any combination of motors being misaligned from vertical. If you can not identify any misalignment then simply offset any motor by a fraction so as to impart a more counter clockwise moment (rotate the motor mount clockwise when looking down the arm towards the body of the copter) If you have telemetry and can monitor the motor outputs in flight, then it doesn’t take many ‘tweaks’ to get all the outputs even in hover…
P.S. - there are a lot of CW/CCW’s in there when considering what is going on and there is no guarantee I got the actual directions correct - try tweaking and see what happens!

10

In this case the motors that are doing the greatest work are diagonally opposite so it does not really make sense that the imbalance is due to an offset in the CG

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11

I submit the imbalance is on the diagonal between motors 1 and 2 such that the frame center of mass is shifted towards motor 1. BTDT.

12

Bad news everyone :frowning:
First, i added screw-nuts between the most cool motor and frame, and looks like things became better http://rgho.st/6sVhtz82G
Second, i disabled this “Low RPM Power Protect” and it stopped losing the thrust and stability when battery goes down to 10>Volts.
And finally, i tried to fly somewhere around the football box at the backyard of the house i live in… and… now it most probably lies on the rooftop of 7 floor building:(((
Last thing i saw was the quad is going down, i pushed up the throttle at max, but it was keep going down and finally disappeared.
Probably the RC Faillsafe RTL was triggered, but default RTL altitude (15M?) wasn’t enough.
The door to the roof is locked and has a seal of the management comany responsible for it.
Tomorrow i will call that company and ask if they can help.
Another thing is that Aomway HD588 DVR often brokes the files on SD Card and now i cannot recover them even by signature to see where exacly the it landed.
Any way, here the last video of that quad: https://www.youtube.com/watch?v=S9gl0kOu9ic that proves it ever existed :slight_smile:
If i manage to get it back, i will post the update.

13

Wouldn’t such an arrangement result in motor 1 taking an increased load?

14

Exactly my point. Motor 1 is getting a higher PWM signal than Motor 2 is. Ergo, Motor 1 is lifting more weight…

15

As per the original post, it is motors 3 & 4 that are getting hot relative to motors 1 & 2 indicating that they are the ones taking the load. This is reflected in the RCOUt dataflash entries:

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