I wanted to discuss the configuration of a large drone
H11M motor with 48-inch propellers.
Cube Orange plus
Arducopter V4.5.7
I followed the methodical setup, but I struggled a lot to reduce the vibrations on the Z-axis.
While analyzing the logs further, I noticed that my motors have a hovering rotational frequency of around 20 Hz.
I was wondering if lowering the INS_GYRO_FILTER to 10 Hz or 15 Hz could be a solution?
I am sharing the logs from one of my tests for your reference.
Additionally, do you think there could be other configuration issues with the drone?
First of all, it is not recommended to reduce the INS_GYRO_FILTER of a copter below 20hz, as it will negatively impact the dynamic response in small ranges. Even reducing it to 15hz is not very effective because this frequency is close to the 20hz of the propeller.
Vibration can be divided into rate and acc. I have tried copters with propellers up to 67 inches in size, and in my experience, if you want to reduce the low freq rate vibration caused by low-speed propellers, the best method is to set a narrow bandwidth RPM based notch filter. Additionally, increasing the minimum takeoff weight helps to ensure the propeller’s vibration frequency is higher than the low-pass filter.
As for the vibration on the acc, this can only be resolved with vibration dampers.
Thank you for your response. I read in the documentation that the notch filter frequency should be higher than the INS_GYRO_FILTER.
In your opinion, with motors running at a speed of 1200 RPM in hover, what would be the correct frequency for these filters?
I also noticed that the Cube Orange+ already comes with built-in vibration isolation. I wonder if further damping would be a good solution?
Regarding the issue that the notch filter’s minimum frequency cannot be lower than the low-pass filter frequency, I tried it before and didn’t seem to encounter any problems. However, considering that the documentation states this, it is recommended to wait for further explanation from the developers.
If it is 1200rpm, then the notch frequency 1200/60=20hz. For large copters, I strongly recommend using an RPM-based notch filter and adjusting the bandwidth to be narrower(8hz). Your ESC should have DroneCAN (I’m not sure, but both X13 and X15 do), you can try reading RPM data through CAN.
Built-in dampers usually only work for high-frequency vibrations (>60hz), and the vibration energy of large copters is definitely beyond what ordinary built-in dampers can handle. I know that some FC have very good built-in damping, but most ArduPilot-compatible FC are not designed with damping for large copters in mind, including your Cube Orange. Trust me, you definitely need external vibration dampers.
I briefly reviewed your log, and it seems that your P value is a bit low. You might want to add some additional load, such as a battery, to increase the minimum takeoff weight. Your motors don’t seem to be very balanced at the moment, and there are some oscillations in the attitude. I suspect your motors might be overheating.
Your MOT_THST_EXPO also needs to be checked, 0.8 might be a bit high. It’s best to calculate it according to the supplier’s table.
Thank you for your responses.
I will set up tests to verify everything.
Regarding MOT_THST_EXPO, I’ve seen on several forums that it should not exceed 0.8.
According to the information provided by Hobbywing, the H11M motors should have a MOT_THST_EXPO value above 1, which is highly discouraged.
As for the notch filters, I have already tested the following values:
Harmonic Notch Filter:
INS_HNTCH_ENABLE = 1
INS_HNTCH_MODE = 3
INS_HNTCH_REF = 1
INS_HNTCH_FREQ = 20
INS_HNTCH_BW = 10
INS_HNTCH_FM_RAT = 1
What vibration-damping systems would you recommend for a Cube Orange?
And are the vibrations in my logs problematic, considering the size of the drone?
The drone, when empty, is intentionally oversized to maximize endurance. It can carry up to 35 kg of payload, with a MTOW of 90 kg.
Regarding MOT_THST_EXPO, I recommend lowering it further. A high value can lead to over-responsive behavior under low load, while a low value can make the response higher under heavy load. I’m not sure of the exact situation, but it’s best to lower it a bit. Currently, your P value is higher than your D value, which I find unusual; I’ve never seen such values in my large drones.
Regarding the notch filter configuration, I apologize for previously overlooking your related parameters, and it’s good that you have indeed enabled ESC telem. I think your INS_HNTCH_BW can be set lower, for example to 8, because under normal circumstances your vibration frequency must be coming from the propeller. Moreover, since you have ESC telem, the RPM data from ESC is both fast and accurate, not requiring much bandwidth to capture the vibration frequency.
On this, I recommend enabling FFT logging; I didn’t see your FFT data, but enabling FFT logging can help you better analyze vibration conditions. Once you identify the approximate range of vibrations through FFT, your INS_HNTCH_BW could be further narrowed, which can improve the high-speed response of your drone.
INS_HNTCH_FM_RAT could also be tried with a lower value. I noticed your rotational speeds are almost all above 1000rpm, so 1000/1200≈0.8. You can try this and observe the effects to avoid situations like continuous gusts, which could cause your notch frequency to consistently exceed the range.
As for vibration dampers, I recommend this: https://www.thingiverse.com/thing:3794194
The normal Vibe values are not related to the drone size; it’s best to keep the peak below 30 if possible, at least when hovering, to avoid many potential issues.
In the parameter descriptions or in the mission planner, the minimum value for the notch bandwidth is 5Hz, does it work well with values lower than that?
The minimum values in MP are just recommendations. When you are certain of what you’re doing, you can try exceeding these recommended values. Of course, the premise is that you are indeed clear about what you’re doing and that the FC will actually accept these values. I haven’t found any cases where the flight controller doesn’t accept values set beyond the recommended ones. Since my drone is too large, I often set values like WPNAV_ACCEL lower than the recommended values to prevent suspended loads from swinging in the air and pulling my drone.
I’m sorry, I made some errors. The suggestion should be 8hz. I misremembered because I often divide these values by two. I hope you don’t mind this mistake.
And I reviewed my FFT again, 2 or 4hz might be too low. From the image, the BW should be at least around 8hz. I’m really sorry, and I hope this didn’t affect you.@Santimt44@aaaa
