HELP! My Propulsion output is limited!?

It’s been popping up more and more on the forums and facebook groups. A message more and more DJI pilots are familiar with but don’t understand;

“Warning: Propulsion Output Limited. Aircraft Motility has been lowered.”

There have been a lot of different stories; It happens with both the DJI Phantom 4 & Inspire 1, when the batteries are too hot, too cold, when the wind is strong, when the battery is low, etc. etc.

It’s time to debunk this message and help you understand what it means and how it affects you.

There are four things we will answer today;

1. How is this message created/generated?
2. What does it mean and does it affect us?
3. What should you do?
4. How can you prevent it from happening?

Let’s get started;

1. How is this message created/generated?

DJI introduced the safety feature as a way to protect the battery from a “Critical Voltage” situation. This means your drone is constantly talking with the smart battery to make sure the voltage and amperage needs for the drone are never exceeding what the battery can supply.

The warning often happens when you perform a manoeuvre that takes a lot of energy, like flying very fast or rapidly elevating. But that doesn’t mean it can’t happen even while you are hovering. It is designed to save your drone from getting a Low Voltage power Cut (LVC) and falling out of the sky.

The lower your battery level is, the higher the risk of receiving the warning. This is because cells become less stable when they are drained.

An example;

Propultion_message

When flying our DJI Inspire 1 Pro with X5 camera on a job a couple of weeks back, I had the message pop up when I was flying full throttle down towards the sunset. I decided to ease off on the throttle and proceeded with the mission. After this had happened, I found it necessary to investigate further into the issue. Like every incident.

The first thing I do when I look into an incident is auto upload my log-file to Healthydrones.com. Healthydrones allows you to look into statistics, issues, maintenance and much more for your drone. It’s a great tool for analysis.

Healthydrones

As you can see the moment where I had the warning message I was pulling a lot of Amps. So much (25-30A amps instead of the normal below 20A level), that at a certain point the drone decided to intervene to make sure no critical issues would come up. Keeping my drone in the air.

A lot of messages say it is purely due to a cold battery, but as you can see below, my battery was at a healthy temperature. It is, however, a combination of battery temp, battery level and voltage drain.

healthydrones temperature

2. What does it mean and does it affect us?

Simply put, when the message appears, the drone wants to save itself from getting a power cut and mitigates the imminent risk. Therefore it will issue a propulsion warning, limit the voltage (and amperage) draw from the battery. It means the drone can not ask for the same amount of power from the battery so something will have to give to stay in the air. Limiting the propulsion output of the drone is the best option to do so.

What noticeable effect does this have?

As DJI says in their warning message; The “Motility” of our drone will be affected. Motility is the ability to move spontaneously and actively while consuming energy in the process (as least in the biological term)

What this means is you might notice your drone is not able to fly as fast or climb as fast, it might drift more easily on the wind, or you might not see any effect at all. It will only limit the propulsion output for the duration it takes to bring the power draw to its normal level.

3. What should you do?

Now, if this message occurs, it is because the drone is working hard, in my case above, it was because it was flying full speed into the wind. Letting go of the throttle is always the best thing to do. Give your drone some time to stabilise itself to it’s normal below 20 amps level. Monitor the drones vital signs on your onscreen display and if you are happy, continue flying. If not, return to home and fly on another battery.

If this warning message is something that happens to you on a regular basis, it is time to investigate more. It could be an inefficient battery, bad bearings, motor failure, propeller, or other mechanical or electronic damage to the drone.

4. How can you prevent it from happening?

One way to minimise the risk is by letting the battery get up to a normal temperature (between 20 and 25 degrees) before starting your mission; you can engage your drone and give it some time to warm up and then proceed to do some hovering to warm the battery up some more. It is worth it getting your battery up to 25 degrees before flying. You can monitor this in the battery tab of the DJI Go app.

Another way is to make sure you land your drone at around 30% (something pilots should do standard) to minimise the risk of voltage dropping as the battery becomes less stable. Bonus is that your batteries will survive longer and that you always have a buffer for when you get in trouble and can’t land immediately.

 

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Written by Rik Roukens
Rik created his personal blog to help people prevent the mistakes he made in the 5+ years he has been flying. His other passions are Photography & videography. Email him anytime @ rik[at]sesh[.]tv or tweet him at @rroukens