Airmode is a feature in Betaflight which can be difficult to understand for beginners in the hobby. In this guide we will try to explain it in layman’s term and help you set it up in Betaflight.
Featured Image is from the movie E.T.
What is Airmode?
Without Airmode, normally when you lower your throttle stick all the way down, the motors on a quadcopter should either stop or all spin at the same speed (depends on how you set it up).
But when Airmode is enabled, it keeps PID loops active when your throttle stick is at zero, which allows the pilots to steer and control the quad even in a free fall. That enables pilots to pull off some crazy aerobatics, and have better control over the entire throttle range.
The Trick to Fly like there was Moon Gravity to No Gravity
Remember in the past when watching those top pilots doing inverted stalls, and it takes forever for them to recover, it feels almost like there was no gravity? I asked myself, do they live on the Moon?
The trick was, they lower throttle as close to min_throttle as possible (so the downward force is minimum when they are inverted), but they didn’t completely kill throttle so PID loop is still working to maintain the aircraft balance.
To avoid accidentally killing throttle and bring the copter into a free-falling rock, some pilots would disable motor_stop (so the motors still spins when you kill throttle), and possibly also assign a switch (aka idle-up switch) to maintain a throttle signal above min_throttle. That’s because PID algorithm would stop when throttle falls below min_throttle.
So why is Airmode Created?
Norbert, a friend of mine explains:
Boris has rewritten mixer logic, which wasn’t too much active at lower throttle ranges, because “we didn’t meant to fly at that range”.
“pid_at_min_throttle” enables the copter to continue process the PID algorithm even at minimum throttle. But pid_at_min_throttle only keeps P and D active, I is zero’ed, that’s why quads could tumble a little while dropping at zero throttle.
That’s why Airmode is introduced which replaced “pid_at_min_throttle“, and it keeps all P, I and D alive even when throttle command is 0.
The difference between Airmode and just disabling motor_stop is that, Airmode allows you to recover more smoothly as you still have control even at zero throttle.
Setting up and How to use Airmode
- First, flash the latest betaflight (2.1.5 or newer)
- In the Betaflight configurator, disable motor_stop, then in Mode Tab assign a switch to Airmode (or you can turn on the Airmode feature which will allow Airmode to stay on on the time)
Assigning Airmode switch – Do you use 2 switches or 1 switch?
In the official instruction, it’s suggested to use 2 separate switches for Arming and Airmode. Some say that because with Airmode enabled, your I term error in PID controller will keep increasing while it’s on the ground. The PID controller will try to correct this error, and eventually the quadcopter will just spool up and might go crazy.
However since then, Boris has implemented a safety feature to avoid “I term wind-up” on the ground. Airmode is only activated if throttle is above min_check for at least 1 sec AND roll or pitch is not centred.
Therefore it seems to be okay now to assign both ARM and Airmode on the same switch. Many people told me that they have been running that without any problems. I tried both, and couldn’t really tell the difference, maybe two switches are just for extra safety.
PID Values and TPA
Some people reported that it’s better to back down your PID a little when using Airmode, because of the more active mixer. Also Norbert told me that TPA is no longer required when Airmode is active.
Here is my first flight with Airmode enabled (very old video).
You don’t normally need to change anything related to airmode. Just enable it and fly.
However some really powerful quads might freak out taking off with Airmode enabled. To ensure reliable takeoff, set the start percentage to a value around your hover throttle value, e.g., for a quad that hovers on 20% throttle:
set airmode_start_throttle_percent = 20
If you are a racer and would like to hold angle on a starting block, set the air mode start percentage to a value a bit below hover point; in the above example, 10-15 would start airmode at a throttle value that wouldn’t make the quad take off.