Hello. I’m the person who has been asking some questions over the past few weeks while developing an MTOW 25 kg-class VTOL.
While I have been struggling with this issue, I came across a post by Merv in the forum thread below, and his comments have been on my mind, so I’d like to ask about it here. (Please refer to the link below.)
In that link, Merv says not to use a fixed-wing ESC as a quad (multicopter) ESC, because fixed-wing ESCs respond too slowly.
I have long been using T-MOTOR V605 KV210 12S VTOL brushless drone motors and FLAME 80A 12S V2.0 Multi-Rotor UAV ESCs as my quad motors and ESCs. However, a friend told me that the 80A has low efficiency and recommended using the AT115A 6–14S VTOL Fixed Wing ESC instead, so I replaced the quad ESCs with the AT115A. From that point on, I began to see severe pitch oscillations from FBWA to QLoiter transition. Please see the flight logs and video links below.
I have two questions:
Merv on the FliteTest Forums said that a fixed-wing ESC should not be used as a quad ESC. Is this actually correct?
In my specific case, do Merv’s comments also apply to the T-MOTOR multi-rotor ESCs and VTOL fixed-wing ESCs I mentioned above?
Thank you very much, as always, for your quick replies and your active support.
Thank you very much for your reply and for pointing that out. As you said, I only followed the procedure up to STEP 8 in the tuning process you shared, and I overlooked the notch filter and QuickTune steps. I agree that I should apply both in future flights.
In our case, we previously built four very similar VTOLs and all of them flew successfully without a notch filter or QuickTune, so I became a bit overconfident and treated those steps as optional. I still don’t fully understand the notch filter, and my first attempt at QuickTune ended in a total airframe loss, which left both me and my teammates quite negative about using it again, especially since these aircraft are team assets, not just my own. Before enabling the notch filter, I feel I need to study it more so I can explain it properly and get my team’s agreement.
Because the previous four aircraft—same layout, only different quad ESCs—flew well even when transitioning FBWA → QLOITER (apart from a small pitch-up), I assumed this new VTOL could also fly without the notch filter and QuickTune. If this were our very first VTOL, I don’t think I would be so quick to suspect “maybe it’s just the ESCs” and skip those steps.
first of all I would like to sincerely thank all of you who took an interest in my problem and helped me with such patience despite your busy schedules. I am especially grateful to @BrownCat, @amilcarlucas, and @GregCovey for their generous support.
In the threads below, you can see how I have been struggling for several months with a newly built VTOL airframe:
Even though I had already built four VTOLs of this type before and successfully completed long-range flights with all of them, this new electric VTOL kept having attitude-control issues only in multicopter mode. No matter what I tried, the multicopter flight was always unstable.
After spending months investigating and studying the problem, the final answer turned out to be surprisingly simple: the ESCs were the problem.
In the threads below, you can see how @amilcarlucas and @GregCovey kindly explained that we should never use a fixed-wing ESC as a multirotor ESC. From my own experience, the main reason seems to be that fixed-wing ESCs respond noticeably more slowly than multirotor ESCs, which causes serious instability on VTOL quad motors. Unfortunately, by the time I found their advice, I had already crashed this particular airframe four times.
Because of this, I would strongly warn others:
Please do not use fixed-wing ESCs for multirotor or VTOL quad lift motors.
I am writing this comment for anyone who is now facing, or might later face, the same situation. I hope you can avoid wasting the same amount of time and money that I did.
For reference, here are the threads where @amilcarlucas and @GregCovey kindly replied with their advice: