You can easily test if this battery internal resistance is the cause: 1) you fly the drone without payload: and then with max payload. You should note the difference. Of course take all precautions to avoid a crash! 2) Another way is to use lipo’s with higher C value: you have lipo’s with 30C to incredibly high values succh as130C. More C value is normally reducing the rate Wh/kg. Check c value of the batteries you now use and double or triple that value to see difference… Success, W
Thank you my friend. This story is about the 42kg spraying drone, no matters I have tuned it, there could not be better.
I am using 12S6P Molicel P42A for the current version. Now all my attentions are about the battery, so I changed it to 12S battery (DJI T20 battery - I modified this from 14S to 12S). I have done it today and conducted a flight test. By analysing the log file, I did not see much different (do you want to take a look? ). However, I am going to make more flight tests and keep you posted.
I am happy to see that you have solved you problem by replacing battery. I wish it happened to me too.
Dear Nuyen, the cells you currently have are doing roughly 11C (45/40)? The other one you are converting makes 9C according to the data sheet. So actually less. Of course, we have to be seeing these values a little careful. Manufacturers are sometimes exaggerating these. But I think that you can try aiming 20 to 25C better, to see difference. GENSACE Tattu might have these. Anyhow, it is still not 100 % clear that the bad behavior is a battery issue… Possibly we should request a official Ardupilot issue to investigate such behavior in loiter. Alternatively can also have a look at the motor thrust and disk loading in empty and MTOW. Cheers and keep us update.
Molicel claimed a single P42A cell can discharge upto 45A. The highest ampere testing setup of this cell I ever seen (in the internet) is just 20A so I guess the overrall C rate is 5C.
I have tried the maximum load of this drone @160A (42kg) and it can handle this weight but there are still some little wobbling in AltHold. When switching to Loiter, it was getting worse. It has been said that without payload (at 23kg) it performs pretty well.
So yes, I also notice the DJI claimed their battery operating at 9C but it is worth trying. I will have some chances to test with Tattu later.
Of course 100% sure it is about the battery but you are the only one who pointed it out and It made me curious and started to suspect my battery type.
Cheers.
Dear Winfriedrijssenbeek,
Congratulations on your heavy lift UAV!
What frame setup are you using? You mentioned using 16 units, and in the picture you posted I can see 6 units from a front view, so I got curious how the units are placed.
I am currently testing an UAV of similar MTOW (~120 kg), but with an traditional hexa frame instead. Large rotors are causing me hard times trying to get the right PID values.
Have you managed to solve the loiter problem?
Best regards
Dear Henrique, sorry your message slipped through. Yes I can explain: there are 8 motors at front and 8 at the rear of the craft. We divided them in 2 units per FC input so 8 connectors to the FC. It is set up at asm octocopter X shape. In the PID tuning we have different values for roll and pitch. The roll is requiring much higher values for P and I. The span is 6 meter and the length only 1.8 meter. When we started we made changes in the motor config liberary for the X 8: You can do that by changing the values for this special configuration. We decided to stop with that as it required updating the library, when going to a higher version of arducopter, and having to be sure all would be compiled properly. It felt to be too complicated.
Today there are also other configs we could use like a H one, but then with 90 degree flattened.
We concluded that the PID different settings in Roll and Pitch is OK. For the extra yaw power the slightly changed the outside motors angle from the vertical to ensure that when a yaw motor would increase its volume, that would also give an extra moment in line with that yaw direction due to the prop thrust effect. So ultimately we got it to fly properly, in all vectors using high values in PI, especially in Roll. Last point, the Roll oscillation we noticed was much improved by using Lipo batteries with higher C values Eg 25C, iso 18650 cell packs with low C values. Best regards
). However, I am going to make more flight tests and keep you posted.