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How drones work

Ansia

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Great video John. I really enjoy watching you smiling while flying the Tello. There is a small error on what you said about the VPS. It isn't the IFR camera, but rather the small camera in the middle of them to keep the Tello steady in one place. The red and black camera calculates the Tello's height against the floor.
 

Guorium

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Great video John. I really enjoy watching you smiling while flying the Tello. There is a small error on what you said about the VPS. It isn't the IFR camera, but rather the small camera in the middle of them to keep the Tello steady in one place. The red and black camera calculates the Tello's height against the floor.
I think higheight is done with the barometer. IR transmitter and receiver sense surface below in approximity.

It is like this small sensor module which has a range about 15cm to 150cm.
 

Ansia

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I think higheight is done with the barometer. IR transmitter and receiver sense surface below in approximity.

It is like this small sensor module which has a range about 15cm to 150cm.
That is what I wanted to say. It does it to prevent going over 30m or land softly. I'm not sure. Need to do some testing.

Excellent, Ansia, do you have a link?
I do not have a link, but rather from experimenting myself. If you tape over the sensor in the middle, you will observe the Tello doesn't hold in place.
 
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Guorium

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That is what I wanted to say. It does it to prevent going over 30m.


I do not have a link, but rather from experimenting myself. If you tape over the sensor in the middle, you will observe the Tello doesn't hold in place.
The IR sensor at that kinda of scale is very short range. It just does not work when it is not even near 2m let alone 30m. Ultrasonic sensors on some other drones can work up to 5-6m on a side note.
 

Ansia

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As you can observe in this Phantom and Evo (Mavic variant), they both have the same small camera for VPS and the speaker looking things are used to create a 3D rendering of the floor in sonar form, so it can see objects when landing.20190301_204636.jpg20190301_204552.jpg
 
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John Gowland

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I wrote
"I am clearly going to episode one again, but that's ok it's all a learning process and will acknowledge people that have helped me in the process.
Even though some of these instruments are complex it's fascinating how they work."
on the PhantomPilots channel.
So are we agreed that the IR sensor is the optical flow sensor is the " The red and black camera calculates the Tello's height against the floor."?
If so what is the camera in the middle?
I sometimes wish I had a bigger brain :)
 

volate!lo

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Camera in the middle feeds the optical flow system.

Big holes beside it are IR transmitter and receiver, used for accurate short range distance to ground.

Inside there is a barometer but naturally this can't be too accurate.

One can see in the log files that there is a lot of (sometimes conflicting) information coming in. Each of these gives some information, and the internal algorithm of the VPS converts this into pretty reliable information about distance, speed, altitude.
 

Ansia

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He developed TelloFPV. The Tello gave him this information as he was programing the app. I understand the need to have info to back up your claim, but you should consider testing as well.
 

volate!lo

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no sources on the internet. That is just the result of my own investigation, analyzing data streams between drone and app.
Once you understand them you will see a couple of different altitude, speed, position data streams obviously coming from different sensors.
 

John Gowland

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I just copied and pasted this from the PhantomPilots I just posted to. Sorry its so long.

This is getting less complex as we go along, but it is starting to make sence.
The attitude and heading reference system looks just like the inertial measurement unit (IMU). Very confusing till I read this.

"An attitude and heading reference system (AHRS) consists of sensors on three axes that provide attitude information for aircraft, including roll, pitch and yaw. These are sometimes referred to as MARG (Magnetic, Angular Rate, and Gravity)[1] sensors and consist of either solid-state or microelectromechanical systems (MEMS) gyroscopes, accelerometers and magnetometers. They are designed to replace traditional mechanical gyroscopic flight instruments.

The key difference between an inertial measurement unit (IMU) and an AHRS is the addition of an on-board processing system in an AHRS, which provides attitude and heading information. Versus an IMU which just delivers sensor data to an additional device that computes attitude and heading. With sensor fusion, drift from the gyroscopes integration is compensated for by reference vectors, namely gravity, and the earth magnetic field.[2] This results in a drift-free orientation, making an AHRS a more cost effective solution than conventional high-grade IMUs (Inertial Measurement Units) that only integrate gyroscopes and rely on a very high bias stability of the gyroscopes. In addition to attitude determination an AHRS may also form part of an inertial navigation system."
Attitude and heading reference system - Wikipedia

So rather than a IMU the more sophistical drones have the AHRS which has the additional "on-board processing system... " and "an inertial navigation system." But they are still referred to as IMU by DJI and other drone manufacturers.
Now the question is does the Tello have a on-board AHRS? It seems as the Mavic 2 and Phantom 4 series definitely have it.

On the Tello channel

"Camera in the middle feeds the optical flow system.
Big holes beside it are IR transmitter and receiver, used for accurate short range distance to ground.
Inside there is a barometer but naturally this can't be too accurate."
volate!lo

In a way it does not matter for the updated video I need to do, bearing in mind it is intended as an introduction for your Joe who does not have an in depth technical background.
It will be difficult enough to explain the middle camera the two black and red either side of it, and a simplified IMU.
The Tello definitely has at least a IMU, it says so in the documentation and in the app in cog, more, 3 dots, IMU status. That must be one small IMU in an 80 gram drone.
So in order to make it accessible and engaging to Joe, a simplified explanation is bound to be technically insufficient but necessary if you get my meaning. Excuse my copy and pasting and to the TelloPilot.
Do I have this right?
 

John Gowland

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It turns out that the barometer is in fact critical for altitude and landing. In combination with the IMU.
"Barometric Pressure Sensor
A high-performance barometric pressure sensor built into the drone precisely measures altitude and can be used in combination with the IMU’s readings for altitude control...."
MEMS Sensors Are the Heart of a Drone | Sensors Magazine
With that in mind I am going to leave the original video up and make another one continuing but explaining as best I can the IMU.
I wanted to add the programming aspect to the Tello anyway, which is probably the best tool/environment to learn how to code.

"Tello EDU is an impressive and programmable drone perfect for education. You can easily learn programming languages such as Scratch, Python, and Swift.
" Buy Tello EDU - DJI Store
 

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