Moon Active Spin
An enduring myth about the Moon is that it doesn't rotate. While it's true that the Moon keeps the same face to us, this only happens because the Moon rotates at the same rate as its orbital motion, a special case of tidal locking called synchronous rotation. Moon active As one of the world’s fastest-growing mobile game startups, we produce engaging entertainment that is enjoyed by players across the universe. Our games have had over 100 million downloads in more than 136 countries worldwide. As the Moon receded from Earth, the planet’s spin period increased and its shape changed dramatically, becoming roughly spherical within a few 10s Myrs. Such a rapid and substantial change in shape.
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This wasn't always the case. Our best guess is that our own moon formed due to a massive asteroid impact, and its initial spin and dizzying 10-hour orbit were almost certainly not in sync with each other, though we don't know which was faster. At such close range, Earth's gravity deformed the moon into a slight oval, with one of its bulges facing Earth. Those bulges quickly swung out of alignment thanks to the moon's asynchronous spin and orbit, but Earth's gravity continually squeezed them back again.
What's more, this gravitational tugging would have influenced the moon's rotation rate. If it was spinning more than once per orbit, Earth would pull at a slight angle against the moon's direction of rotation, slowing its spin. If the moon was spinning less than once per orbit, Earth would have pulled the other way, speeding its rotation.
Whatever the case, it took just 1,000 years for the Earth's pull to adjust the moon's spin enough that one rotation of the moon corresponded to one trip around the Earth, leaving one side forever locked facing away.
We do end up seeing some of that far side because the moon's elliptical orbit gives us peaks beyond its average eastern and western horizons, and its tilted axis causes moon seasons, revealing more of the lunar north or south poles. But those glimpses only add up to an extra 9%, leaving 41% of the moon hidden from Earth. Satellites starting with Luna 3 have allowed us to map the rest, but it's safe to say that our relationship with the moon is still pretty one-sided.
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.
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.
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?
Moon Active Free Spins
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.
Moonactive Spins
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.
- 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
Moonactive Free Spins 2020
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.