We don’t have a better idea of vibration, probably because it’s an internal combustion engine. In particular, the ground vibration problem caused by the change of the cyclic pitch and the collective total pitch is troublesome. The only way I can think of is to shut them down on the ground.
I think a large part is due to the engine. I know a user that would balance his pistons/crankshaft to achieve lower vibrations. From what I understand some engine manufacturers are better than others on this. You may want to look that up. I don’t work with gas engines.
Thank you very much. I will study the materials you sent and try your suggestion on parameter adjustment. After I finish testing, I will continue to give you feedback.
By the way, the helicopter doesn’t hover very well in Loiter mode. It swings, especially when there is wind. Could you give me some advice on parameter tuning through the log?
Do you mean the POLINI THOR 250 DUAL SPARK engine？I’ve heard of similar treatment.
Hello, Bill. If we lower the lowest collective pitch，in your opinion, whether the vibration will be better on the ground？For example，we adjust the lowest collective pitch from 1° to -2°. The max collective pitch is still 8°. However，the hover Aout will be about 0.8 or more. Is it a problem？ （Because the hover collective pitch “Aout” is suggested 0.2-0.8）
Don’t know much about these. Here is a post from a user whom I was referring to. He mentions a little bit about counter weights on the crank shaft to reduce vibration. But he also mentions what engines worked best for him.
Probably not. As you get more negative collective pitch, it will probably get worse. but I would suggest that you give yourself at least -2 deg for the minimum.
I would suggest increasing your rotor speed to keep within this range. You may be running your rotor speed to slow if you are near 0.8.
Yes, you are right. However, the power of the engine is limited. Thanks for your contribution. Today, according to your suggestion on the forum, I adjust the Angle-P from 3.5 to 6. The state in the loiter mode become better. I’m happy.
I hope that my problem about the resonance could be solved later.
Happy new year!
Glad to hear you were able to get a better tune.
There is nothing from a code perspective that ardupilot can do to help with this. Vibration is something that has to be managed mechanically as much as possible. I have never encountered a user with the vertical vibration like your helicopter. Leonard and I will look at how it affected the altitude controller out of curiosity and determine if this an issue for more reasonable levels of vibration.
Happy New Year!
Thanks for your information.
Your reply is the best gift for my new year, haha. I am glad to receive your reply. I appreciate it.
As you said, judging the landing requires high reliability. Manually switching modes to turn off pids runs the risk of forgetting or misoperating. Yesterday, I added 70g counterweight to the damping plate of the flight controller. Vibes and ACC.x went down a bit more. So far the altitude holding seems acceptable, but the positioning accuracy is mediocre and the uav will wobble in the loiter mode. We also try to set PSC_ACCZ_FLTE from 20 to 10, and its effect is not obvious. Adjusting the Angle_P from your suggestion is helpful.
Thank you and Leonard for your contributions. Your work is great and worthy of expectation. Now the vibration of helicopter flight has been reduced a lot, but the problem of ground resonance is still difficult to optimize. Yes, ground resonance is mainly a mechanical problem, but it’s hard to avoid for oil powered helicopters. According to the current situation, excessive cyclic pitch and total pitch operation during resonance will aggravate the resonance situation and even bring the risk of uav rolloping. I have no good way to optimize it at the moment, and I look forward to your further suggestions and ideas.
Yesterday, we lowered the collective minimum pitch to -1 degree, which I think brings up the grip of the DRONE on the ground. It seems to have no good or bad effect on vibration. Now the hovering Aout is about 0.75. Is there any potential safety hazard? If the lowest collective total distance is -2 degrees, I estimate the hovering Aout to be 0.8. What is your main consideration about -2 degrees? Please advise.
Your suggestion to increase the rotational speed should be effective. But now we have a defined driveline, so for the internal combustion engine, the rotation speed is difficult to adjust. The speed at the rotor tip is now 0.5 Mach. Also, if I turn up the rotor speed, I worry that the engine will not be able to carry the current maximum collective total pitch.
The altitude controller responding to inputs when it is armed but landed with interlock disabled. We found that in 4.0.7, when the UAV was on the ground, the altitude control integral was a horizontal line, but in 4.1.2, the altitude control integral danced violently and was of great value. In fact, the Z vibration of 4.0.7 in the log is larger than that of 4.1.2. In addition, in 4.1.2, the desired height and climb speed are consistent with the actual measured height and climb speed. This is probably why 4.1.2 is in worse condition than 4.0.7.
Could this problem be optimized? Now I’m very disturbed. For this reason I dare not upgrade to 4.1. But in 4.0.7 when using GPS for yaw, there will be a bunch of alarms about compass.
@bnsgeyer @Leonardthall
The day before yesterday（2022.1.4）, I flew auto mode in 4.0.7. After the helicopter lands, the initial collective pitch is the lowest (Aout 0). As the helicopter pulled out of cruise control, the collective pitch suddenly reached its maximum (Aout was 1) and the aircraft lifted off the ground again, threatening to roll over again.
This is the log:
A small piece of code I modified in AP_MotorsHeli_Dual. CPP in 4.0.7, I wonder if it is feasible? My logic is that when the helicopter is armed and has no cruise control (! Interlock), so that all rotor servos in the lowest collective picth position. So that when the helicopter idling or landing after the exit cruise, the helicopter is the lowest collective pitch, and not flips or rollover.
We’d like to hear your professional opinion. Thanks for your time.
Best wishes!
@Flying2015 This was not the fault of the autopilot. The pilot initiated the motor interlock (rotor spool down) and caused this problem. The autopilot still thought it was flying and is why it raised the collective. the pilot cannot interfere with the autonomous mode by switching off the motor interlock. the pilot has to let the autopilot initiate the shutdown process otherwise the pilot should switch to a manual throttle mode like Stabilize or Acro before switching off the motor interlock.
@Flying2015 Thank you for pointing this out. I agree that the two versions are handling the altitude controller on the ground differently. Adding more to your story, here is a plot of 4.0.7 on the ground. These plots are similar to yours but I added the PIDA.P signal also along with the CTUN.ThO which is the output collective. You can see that the I term is constant where the P term is pretty large but the collective out is low and not causing any problems.
Here is the same plot for 4.1.2. with this version, the P term is low and the I term is very high. The resulting collective output is high as well.
Overall I think there is merit to your concern. I was looking at the function that relaxes the altitude controller and it has changed quite a bit. I will discuss this with @Leonardthall. I am concerned with the I term building like it does when the altitude controller is supposedly in a relaxed state. These are extreme conditions that you provide but I think this still is valid for lower vibrations states. The integrator should not be allowed to build in this manner in a relaxed state.
Thanks again for your persistence in this matter.
That’s true, your observation is very careful, it is really our manual operation. Thank you very much for your reply, it is so crucial!
Yes, our situation is quite extreme. The vibration of a real drone is very high, which also bothers us. We want to make progress on this, but it is too difficult at the moment. Thank you for your patient reply. I am very happy to get your attention and look forward to it.