GPS+compass module mounted on a 25cm long carbon fibre standoff to avoid magnetic interference with other components
Frame: Foldable “Alien 680mm” clone frame frame with an additional 3mm thick carbon fiber plate for mechanical stiffness
Battery pack: 6s3p 21700 EVE 40PL pack
The drone was configured and tuned with AMC. During the setup and tuning process everything went pretty well.
During loiter in wind-free engironment two motors are rotating higher RPM than the other two motors. At the end of the flight those motors are warmer than the other ones.
Motor “A” and Motor “C” was warmer than the other to mots.
The propellers are new, there are no mechanical damages on them.
The motors are rotating freely, there is no bearing damage, no “strange noises” when I rotate them with hand.
I have re-aligned the motors with a long metal ruler, to double-double check for slightly incorrect motor orientation (“yaw imbalance”) - no effect of the re-alignment
The only difference I can think is the different length of wiring due to the location of ESC: ESC is not in the middle of the craft, it is moved towards the back a little bit.
I assume, this is not normal, the 4 motors should have almost equal RPM when the craft is mechanically fine and there is no wind while the quadcopter is just hovering.
What is the acceptable RPM difference between the motors?
WHAT IS BELOW IN THIS COMMENT IS MOSTLY INCORRECT, I MISREAD DEFAULT VS ACTUAL FRAME TYPE
Your frame type is Betaflight X (FRAME_TYPE = 12), where:
servo function 33 maps to rear right motor,
servo function 34 maps to front right motor,
servo function 35 maps to rear left motor,
servo function 36 maps to front left motor.
And your servo assignments are as follows:
SERVO1_FUNCTION = 34: so, front right motor (the RPM of which is plotted as RCOU.C1)
SERVO2_FUNCTION = 35: rear left motor
SERVO3_FUNCTION = 36: front left motor
SERVO4_FUNCTION = 33: rear right motor
As a result, you have more RPM on the right than on the left, and no other significant difference. This is not yaw imbalance, this is weight imbalance.
P.S.: there is also slightly more RPM on the rear than on the front, which is again quite likely due to weight imbalance.
Thank you for investigating!
What weight imbalance can cause this?
As far as I know my biuld everything is simmetrycal to the longitudinal axis of the drone, except one component: a camera holder, about 50-80gramms. It is shifted out of centerline with about 20mm.
The drone TOW when the logs were recorced was about 2800gramms.
Can this cause this imbalance?
I will check the distance of motors from the centerline, maybe that is not perfect.
If this a huge issue?
Can I fly safely with this imbalance?
Something didn’t look right here. So with another look at the log the FRAME_TYPE is set to 1 for a typical Quad/X. Also seen in the messages. So the Outputs with higher PWM output are the Rear Motors 2&4. So, just shift the battery forward…
The wiring order can be completely random. All that is important is the Motor assignments (Motors 1 thru Motors x) produce the right positions on the frame for the selected FRAME_TYPE.
As I posted in another thread awhile ago (it was a quad): My point is it doesn’t matter what Frame Type you select (1,12,13,14 or 18), and you can initially wire them in a random order. Run Motor Test, determine if the order and direction is correct for the frame type and if not re-factor the servo outputs and motor directions and go.
It doesn’t help that I confused things here in this thread and then compounded it with a useless test…
The FC location is indicated with the green dot, almost at the middle of the craft.
The ESC is located at the blue dot.
ESC is connected according to the red arrows.
The battery pack can be mounted onto the white slicicone strips with velcro tape.
The exact location of the battery pack is not guided by anything. I need to draw a line, where to locate the battery.
On the bottom side there is the off-center located clamp, to hold the gimbal and camera. During hover test there was no payload.
everything is simmetrycal to the longitudinal axis of the drone, except one component: a camera holder, about 50-80gramms. It is shifted out of centerline with about 20mm.
