Mini 4 Pro Unstable on the pitch axis

[Sp1k3]

Have anyone else noticed that the pitch axis of the M4P is unstable at different speeds with the battery plus on it?
The causes significantly decreased flight time. Is there any way we can change the pitch PIDs?

 

[slup]

No... the PID values are hidden within the firmware for a DJI photo drone.

 

[Cafguy]

That would be great for some of us and tragic for most. Ebay would be crammed with crashed drones for sale.
It would be nice to be able to tune a DJI camera drone BUT it will never happen at least not thru DJI.
Your problem is probably with the wind NOT the Tune.

 

[tuxtard]

Can you post a video of said instability so that we know what exactly are you talking about?

 

[TinajaEco]

Have anyone else noticed that the pitch axis of the M4P is unstable at different speeds with the battery plus on it?
The causes significantly decreased flight time. Is there any way we can change the pitch PIDs?

Actually yes, but only into the wind and only occasionally. It starts to “buck” for lack of a better term.

I figure it was designed around the original battery and the larger batt changes the balance center point.
Maybe.

 

[slup]

...I figure it was designed around the original battery and the larger batt changes the balance center point.
Maybe.

A changed CoG shouldn't make the pitch axis instable (if the motors doesn't reach max revs)... if heavier in the rear the Flight Controller will command higher revs on the rear motors to generate more thrust to compensate & position the drone in the commanded tilt angle.

If the drone is affected by a headwind will not make any difference... it's only the ground speed that will differ, & it's equal if it's gusty... there the speed will be jerky.

A strong gusty tail wind might cause the pitch to be unstable... this as the drone have a max specified speed. If some gusts really pushing the speed up, the drone will pitch up to lower the speed, then when the gust have passed, the drone again needs to pitch down to keep the speed up.

If affected by a really gusty strong side wind pitch might be jerky, nothing of the tilt is left for pitch if the drone needs to utilize a lot of roll to hold against some gusts... the drone is limited with a "tilt"-angle, meaning a combination of pitch & roll, so if roll use all available angle to minimize drift, less remains for pitch.

The first thing I would test is to change the props & see if that improve thing's...

If you share the flight log from a flight where this happens we can clearer see all that happens.

 

[TinajaEco]

If you share the flight log from a flight where this happens we can clearer see all that happens.

Copy. Next time it happens bad enough that the gimbal can’t compensate, I’ll post that up.

FWIW, it happens in headwinds and near canyon edges, but infrequently. I live in canyon country and when the drone is in the cliff to flat transition zone, that turbulent air is what generally causes the “bucking”. If I back off the sticks and slow down, the bucking stops.

I’ve never pulled a log, so it’ll be good practice on that for me.

 

[slup]

...I’ve never pulled a log, so it’ll be good practice on that for me.

Go here & upload the log which is stored in the screen device you flew with --> PhantomHelp Log viewer
Then share the link they provide once you've uploaded in this thread, in a new post.

(Scroll down a bit there & they describe exactly where in your screen device the logs are stored)

 

[Sp1k3]

guys I contacted DJI and they told ne to calibrate the IMU. I honestly didn’t believe it would work. BUT I was wrong!!
As soon as I did it immediately eliminated the problem!!

 

[tuxtard]

This happens to me as well, but IMU calibration did not help. It starts oscillating in head wind but it will not stop on its own and I have to reduce throttle or completely stop for it to regain balance.

Here's the flight log: DJI Flight Log Viewer - PhantomHelp.com

Timestamps of the issue:
1:22 - 1:29
6:02 - 6:14
20:07 - 20:10
20:36 - 20:42

Does anyone has any suggestions what could be the issue, other than this unit just being a dud?

 

[TinajaEco]

Thank you for uploading the log. I had the issue again last week and have not figured out how to download and post it from my work IOS setups.

 

[BudWalker]

This happens to me as well, but IMU calibration did not help. It starts oscillating in head wind but it will not stop on its own and I have to reduce throttle or completely stop for it to regain balance.

Here's the flight log: DJI Flight Log Viewer - PhantomHelp.com

Timestamps of the issue:
1:22 - 1:29
6:02 - 6:14
20:07 - 20:10
20:36 - 20:42

Does anyone has any suggestions what could be the issue, other than this unit just being a dud?

This is similar to behavior seen with an Avata that had been modified with larger motors. I'm assuming your Mini 4 Pro is not modified? Have you replaced some props recently?

Loss of control after upgrade

Looking at the first example, [82 - 89] secs, it can be seen that both pitch and, to a lesser extent, roll are oscillating at about 2.5 hZ. Further, there is a phase difference of about 90°.

There are other events where the oscillations weren't as extreme as the ones you cited; e.g. [1213, 1216] secs. The cited events all occurred when flying into the wind while the Mini 4 was close to max pitch forward. It would be interesting to see if this happens flying backwards.

My advice is to contact DJI and return for either repair of replacement. You might want to first check the props; no nicks, no loose screws, etc.

 

[tuxtard]

Thank you for uploading the log. I had the issue again last weeks db have not figured out how to download and lost it from my work IOS setups.

You're welcome

 

[tuxtard]

This is similar to behavior seen with an Avata that had been modified with larger motors. I'm assuming your Mini 4 Pro is not modified? Have you replaced some props recently?

Loss of control after upgrade

Looking at the first example, [82 - 89] secs, it can be seen that both pitch and, to a lesser extent, roll are oscillating at about 2.5 hZ. Further, there is a phase difference of about 90°.

View attachment 173997There are other events where the oscillations weren't as extreme as the ones you cited; e.g. [1213, 1216] secs. The cited events all occurred when flying into the wind while the Mini 4 was close to max pitch forward. It would be interesting to see if this happens flying backwards.

My advice is to contact DJI and return for either repair of replacement. You might want to first check the props; no nicks, no loose screws, etc.

It is a stock, basically new M4P. This started happening from the first flight, it's not something that appeared after prolonged use. Props are undamaged and screws are tight. On this flight I used Plus battery. The same issue also appears with the normal battery, but it is less frequent and less prominent.

 

[GerdS]

I also remember this problem from my M4P, especially while flying with higher speed and some wind influence (standard batteries). So it's a general problem, not just some individual drones.

 

[slup]

...Does anyone has any suggestions what could be the issue...

This is similar to behavior seen with an Avata that had been modified with larger motors.

My advice is to contact DJI and return...

I also remember this problem from my M4P...So it's a general problem, not just some individual drones.

I think this is a PID tune issue...

Yeah I know, most photo drone pilots are blissfully unaware about PID tuning & even what the PID's are... but if you're into FPV quads (others than the Avata & DJI FPV) you know that the P, I & D loop is crucial when it comes to getting a quadcopter to fly properly.

The driver behind the P,I & D loop is a comparison between the gyro (what the drone does in reality) & the stick input (how you want the drone to behave). Once the flight controller notice a deviation between these, the P value reacts & tries to close the deviation with full force... the D value acts as a damper that keep track on how quick the deviation is closing & brakes the P's "push" so the drone doesn't overshoot the commanded movement. If P or D is tuned wrongly or on the "edge" thing's like full commands & changed weights can cause oscillations. The I value have less impact on oscillation problems as it's main purpose is to handle thing's like change in center of gravity & long term uncommanded attitude changes.

All this is easy fixed for a FPV quad as you have access to the PID values & can tune for changes in weight, thrust (using other props) & changes in CoG (where you place the battery & if using a GoPro or not)... but for a DJI photo drone the PID's are locked into the firmware & you can't change anything.

-If the problem gets larger when using the heavier battery
-If this is noticed by several Mini 4 Pro pilots
-If some see signs of oscillations even with the standard battery... and some doesn't

All points to that the DJI Mini 4 Pro is tuned to max with very little headroom for changes in mentioned weight, CoG & prop condition (thrust generation)... and this can for some lead to oscillations.

Agree with @BudWalker ... send it in.

 

[tuxtard]

Thank you @BudWalker for the log analysis and thank you @slup for your explanation. Because sending drones back from my region is painful I would like to make sure that this is not a firmware / design issue, and not just my unit. There are at least 4 of us here that are experiencing the same issue. If we attract enough attention on the official forum maybe DJI engineers will take a look at these logs and tell us if it is fixable by a firmware update, or we actually ended up with faulty units. I previously crated this thread on the official DJI forum, but still did not get any response from DJI: Mini 4 pro oscillating

 

[BudWalker]

Thank you @BudWalker for the log analysis and thank you @slup for your explanation. Because sending drones back from my region is painful I would like to make sure that this is not a firmware / design issue, and not just my unit. There are at least 4 of us here that are experiencing the same issue. If we attract enough attention on the official forum maybe DJI engineers will take a look at these logs and tell us if it is fixable by a firmware update, or we actually ended up with faulty units. I previously crated this thread on the official DJI forum, but still did not get any response from DJI: Mini 4 pro oscillating

You could try a PM to one of the moderators on the DJI forum. Also try contacting DJI tech support via email, phone or chat. Per @slup 's post I suspect it's fixable with a firmware update. Good luck.

 

[Droning on and on...]

If it's a matter of PID tuning as @slup outlined, and I agree this is 99% likely what the solution is, we'll see this fixed in a future firmware update. Since we know the battery type is detectable, this may simply be a matter of separate PID values for the different batteries.

If this is the problem/solution, any help we can give DJI in reliably reproducing the problem will make a big difference. PID tuning is near impossible if you can't measure the effect.

 

[tuxtard]

If it's a matter of PID tuning as @slup outlined, and I agree this is 99% likely what the solution is, we'll see this fixed in a future firmware update. Since we know the battery type is detectable, this may simply be a matter of separate PID values for the different batteries.

If this is the problem/solution, any help we can give DJI in reliably reproducing the problem will make a big difference. PID tuning is near impossible if you can't measure the effect.

I agree. It might help if others who experience this issue send their logs to the following official DJI forum thread: Mini 4 pro oscillating