Drone keeps dropping down then lifts up

I’m having this issue where the drone is dropping to the floor without time pushing the throttle down. It does pick itself up again but continuously does that until I push the throttle higher.
I’m using Pixhawk.

.bin log file

This is a video to show what is happening.

You’re in stabilized mode with default tuning. It’s not going to maintain altitude. In stabilized mode the flight controller is just keeping it spinning side up, it’s up to you to manage the throttle for altitude control.

Continue with the tuning process as per the wiki and test it in test in Alt-Hold. Once that’s tuned it should stay in place with neutral throttle.

I actually didn’t know that for stabilize it would not (hover). In the video, you can see it drop all the way down to the ground. So, that means that if I use a different Flight Mode (Alt-Hold/Loiter) I can make the drone stay stable and hover?

Also, there isn’t anything wrong with the drone, it’s just some parameters and the flight mode?

I can’t say 100% there isn’t anything wrong, but I will say that what you’ve described and what I saw in the log look pretty normal to me. Your parameters aren’t wrong, they just aren’t tuned yet, and the mode is doing exactly what it’s supposed to do.

Since we’re talking I looked at a couple more things:

The vibration levels are a little high on the Z axis. Maybe have a look at your props and make sure nothing is bent and they are all tracking properly. Otherwise you may need to add some damping to your controller mounting.

The motors are running a little high. They aren’t maxed but you’re at the higher end of where you want to be for performance. Either the quad is too heavy, the props are wrong, or the battery voltage sag is too much. If that’s a LiPo battery the voltage is way too low. If it’s a LiON it may not have C rating for the machine.

The battery is a Lipo 3s 11.1V 5200mAh 80C.
The total weight is about 2.4 lbs

I keep getting confused with tunning. I thought that’s what I did when I did the Mission Planner Helper. It should tune everything automatically or am I misunderstanding this?

You’re using stabilize mode. This is a mode in which both altitude and posture require manual control.
The modes I usually use are Alt-Hold mode and Loiter mode.

Alt-Hold mode maintains altitude, while posture must be controlled manually. In addition, Loiter mode maintains altitude and posture by the aircraft itself and uses GPS.

These two modes require the throttle to be raised to a certain point at take-off to hover the airframe, and then the throttle of the control to remain neutral.

Since the Loiter mode uses GPS, it is not recommended when an EKF error occurs.

(Please understand that my mother tongue is not English.‘v’)

First the battery: That battery voltage is too low for a Lipo. You’re starting the flight below 3.7v/cell, and already some will say that’s too low to start a flight. The battery dips below 3.4v/cell, doing that repeatedly will eventually ruin the battery. The current meter isn’t showing any useful data so it’s hard to say if it’s the chicken or the egg.



  1. Mission planner helper sets up the initial tune. A safe starting place. Since Arducopter can fly machines from sub 250g to over 250kg with many different configurations, the default tune simply cannot work for all. The Mission Planner helper sorts out that initial point so everyone stands fighting chance of a successful first flight.
  2. Initial test flights. This will set up Alt-Hold (what we were talking about earlier), and the filters. <<— very important.
    2.5 I add to this step that I check the vibration. If the vibration is bad (and yours could use some improvement, but it’s not the worst by far) get that sorted before you move on otherwise you’re just wasting time.
  3. Evaluation of the tuning. In some cases the initial tune isn’t enough to proceed to autotune, so you need to give it a better start. At this point though you have some data and observations to work with.
  4. Basic manual tuning if the evaluation isn’t satisfactory. Autotune in the next step will push the quad with what is basically a full stick deflection. Before you can autotune the initial tuning needs to be at least good enough for the quad to withstand these inputs without losing control.
  5. Autotune. If the evaluation is good, or the basic tuning is done, you can go on to autotune. Many people jump to this too early and then that’s when things go wrong.
  6. tweaking the tuning for your taste. The most subjective part. What you want to fly, and what I want to fly may be totally different so this is where you make it your own.

@Allister Your feedback is insightful. I have been building/flying for a while, yet smart log analysis is still a weak point for me. I have yet to find a simple step-by-step guide for doing this, ie, knowing what to check, how to interpret the information, and what corrective actions to consider.
Perhaps you might create one :slight_smile: ?

Regarding tuning, much emphasis has been placed by others on notch filters. Would you list that as essential? Too bad there isn’t an auto feature to configure it.

The closest to that is to use FFT reference for the Notch Filter. There are some parameters that can be tweaked but it will typically function OK with defaults.

Where can I set the flight start voltage? I thought that the BATT_ARM_VOLT is the one that starts the flight as long as the battery has the required voltage.
The motors I’m using require 7-12 volt. Apparently, a 4s battery will be too much.

I think it depends on you’re gear. I’ve built drones that fly so well on stock defaults that I haven’t bothered to do any significant tuning because I didn’t think I could make it much better. I’ve also had others that were un-flyable until the tuning was addressed. Generally I’m going to say that you should go to the FFT graphs and set up the notch filters. You only stand to make improvements so there’s nothing to lose and it only takes a few minutes (once you’ve done it a few times :slight_smile: )

As for the logs … Just dig in and start looking at them. One thing that will really help is look at the logs that get posted here on the forum and follow along with the analysis of some of the smart people (that’s how I got started). You’ll notice that may of us here have our own starting points and key things to look at based on what’s kicked us in the butt over time. There isn’t a real step-by-step guide to looking at logs, because no two are the same. And don’t be afraid to ask about a log analysis on a thread. I don’t think it’s off topic if someone is looking to learn more about something asks me how did my analysis.

Correct. But yours is set to 8v. That would let the drone try and fly down to 2.6v/cell. Your Lipo would have been destroyed at that point. I should clarify that I posted the voltage in Volts per cell, not the total voltage. I tend to work that way because it doesn’t matter if your using 3S, 4S or 6S, the process is the same.

Others may have different opinions but for an arming voltage I would suggest something above 3.7v/cell, (11.1V on a 3S battery) Even that is low but it let’s me do some quick checks and ground testing without too much trouble. Maybe set it even higher if you’re unsure, like 3.9 v/cell (11.7v on a 3S.) You can still fly below this voltage, BATT_ARM_VOLT will only stop you from arming.

Because I’m the type of person that stares at the battery voltage as he’s flying I’m actually a little lazy with by battery failsafes because I know I’m paranoid about it. If you are the type to drive around with the low fuel light on for days at a time then you might want to set the battery failsafes and warnings higher so you don’t get caught out.

I would check that. A full 3S battery is 12.6v. There may be a rounding error, or something lost in translation but If your motors can’t handle 3S then they are too small, or poor quality, or just intended for something else.

That’s odd because I’ve been looking for different lipo batteries and all 3s are 11.1v.
Unless I have to charge it all the way to 12.6v.

Here’s a quick primer: Lithium Polymer Etiquette: a Comprehensive Guide to Working With LiPo : 9 Steps (with Pictures) - Instructables

LiPo battery cell voltages:

  • 4.2v is fully charged
  • 3.7v is nominal charge. Think of this as a safe resting or storage voltage. You can take this up to 3.8v.
  • 3.5v is minimum safe voltage for good battery health. With many quads, assuming the battery is specd correctly, if you fly it down to 3.5v it will recover to 3.7v after you take the load off and check the cells.

It’s just the way they sell batteries, they list them by the nominal voltage of 3.7 but you need to charge it to 4.2.

I see. Thanks for the information.
The motors I’m using are 920kv. Props are 10’.
Although, the seller suggested using a 3s battery.
I had a 4s before when I first bought all the components, but never got to use it (I returned it), thinking it would damage the motors for excessive power.

Hard to say. I have 920Kv motors with 10" props and no issues with 4S. Depends on the motor/ESC/prop. Some people are able to make that analysis in their head but I’m not smart enough. Sites like ecalc.ch can help you figure out what to use. A subscription will cost a couple of bucks but if you’re making buying decisions you’ll save the money right away.

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I guess I should have specified a bit more. I will mostly be using the drone for autonomous flight.
In that case, would the drone stabilize and hover itself compared to me who would have to control the pitch/roll/raw?

Have you read this page?