I’m having a major issue with my new heavy-lift octocopter. During flight, some of the motors intermittently cut out or drop to a lower RPM, while others compensate by increasing RPM to maintain thrust. This makes it incredibly unstable and unsafe to fly.
Here are the specs of my build:
Frame: 1900mm center-to-center distance
Propellers:29 inch
Motors: T-Motor U8
Flight Controller: Cube Orange
ESCs: T-Motor Alpha 60A
-GPS:Here3+
I’ve checked for obvious issues like loose connections and prop damage, but everything seems fine.
Any ideas on what could be causing this problem and how I can troubleshoot it?
At the very least we’ll need a logfile where the issue can be retraced.
The configuration howto linked by amerilucas is a very good idea as well. I don’t have much experience with heavy lifters, but the design looks like there might be many oscillations to filter out.
if your drone frame looks exactly like the diagram, CW motors are under-mounted, and CCWs are top-mounted if I understand correctly. Do you think the propeller tip-to-tip is too near even though is up and down? Potentially of propeller vortex or prop wash disturbance.
What is the drone takeoff weight? what is the MOT_THST_HOVER after learning? Is it very low?
Does each motor distance (radius) to the center of the frame still resemble to Octo X motor layout?
4 motor are installed downward and 4 motor installed upward.
1- motor A = downward
2- motor B = upward
3- motor C = downward
4- motor D = upward
5- motor E = downward
6- motor F = upward
7- motor G = downward
8- motor H = upward
there are about 3 inch overlap on each other.
The max take of will be 27kg. and the distance of each motor is same to the center (design is symmetric).
Potentially overpowered, we have a hexa 30" propeller 25kg, motor spinning at the low motor curve. Octocopter, we use 2388 propeller with X6 hobbywing motor already operating at the low curve.
Unlike OctoQuad, the undermount motors may have experience uneven prop wash, my guess.
I foresee your Test AltHold flight will be scary.
The pilot should not take off in AltHold until the altitude controller has been tested in flight. This should be done by taking off in Stabilize and switching to Alt Hold. While Alt Hold is rarely a problem unless the aircraft has a very low hover throttle.
I would reduce MOT_THST_HOVER to 0.1 or 0.12. your drone is so big, and if you use a spring-back throttle stick RC, I recommend you have a friend help you switch when doing Test alt-hold. practice without propellers installed. It may climb very fast when switched.
Now the frame vibration is high, could be due to the 3" overlap prop wash, not sure. Confirm it again under Althold.
The design is for operation at an altitude of 1200 meters above sea level in mountainous terrain and challenging atmospheric conditions, including turbulence and wind speeds averaging 5 to 6 meters per second.
The manufacturer did that for 22x6.6 with 150KV. You probably can estimate it with propeller equivalent estimator.
If you look across their different prop size test data, I am not very sure, your pitch 7.9 and the existing test data is 6.6, my guess it may not give you better lift. If you can find 24.2*6.6, maybe it will give the drone more lift.
