How drones work

I found this......Good information and if your looking for something to invest in...no telling. "By Sergej Scheiermann. The heart of the drone is its Attitude Heading Reference System (AHRS) which includes inertial sensors, magnetometers and processing units. The AHRS estimates the device’s orientation, for example roll, pitch and yaw angle. The sensor’s inaccuracies such as offset, sensitivity errors or thermal drifts lead to orientation errors". One of the key factors in this improvement has been the use of high-performance micro-electro-mechanical system (MEMS) sensors. The market for sensors in drones is growing fast: Based upon data from IHS Markit (Motion Sensors for Consumer & Mobile Devices – 2017) the market for MEMS motion sensors (i.e. accelerometers, gyroscopes, IMUs and pressure sensors) in drones and toy helicopters is expected to reach in total approximately 70 million units until 2021, with a CAGR 2018-2021 of 17 %. "

MEMS Sensors Are the Heart of a Drone | Sensors Magazine
 
I found this......Good information and if your looking for something to invest in...no telling. "By Sergej Scheiermann. The heart of the drone is its Attitude Heading Reference System (AHRS) which includes inertial sensors, magnetometers and processing units. The AHRS estimates the device’s orientation, for example roll, pitch and yaw angle. The sensor’s inaccuracies such as offset, sensitivity errors or thermal drifts lead to orientation errors". One of the key factors in this improvement has been the use of high-performance micro-electro-mechanical system (MEMS) sensors. The market for sensors in drones is growing fast: Based upon data from IHS Markit (Motion Sensors for Consumer & Mobile Devices – 2017) the market for MEMS motion sensors (i.e. accelerometers, gyroscopes, IMUs and pressure sensors) in drones and toy helicopters is expected to reach in total approximately 70 million units until 2021, with a CAGR 2018-2021 of 17 %. "

MEMS Sensors Are the Heart of a Drone | Sensors Magazine

Nice article - thanks for posting the link.
 
Actually the barometric sensor isn't going to detect such a small vertical displacement. Positional stability, horizontal and vertical is primarily provided by the IMU, via the accelerometers. The barometer is just providing absolute values to compensate for bias and drift in the accelerometers.
"Actually the barometric sensor isn't going to detect such a small vertical displacement. " Is there technical info to support this statement/sensitivity of DJI barometers, et al? I like facts v. assumptions. An honest question.....
 
"Actually the barometric sensor isn't going to detect such a small vertical displacement. " Is there technical info to support this statement/sensitivity of DJI barometers, et al? I like facts v. assumptions. An honest question.....

Sure. The MEMS sensor article linked above gives a typical relative accuracy, which amounts to around 0.7 meters vertical. Or you could look at the raw pressure data from a DJI aircraft - below is the pressure, in Pa, for a stationary Mavic Pro as the pressure sensor warms up.

raw_barometer_Pa.png


A couple of things to note. Ignoring the change from start to finish, which amounts to around 60 Pa (equivalent to around 6 m vertical displacement), we can instead consider the higher frequency stability of the pressure reading. For a typical 10 second window the standard deviation is around 5 Pa, equivalent to around 0.5 meters. The noise amplitude is 10 times that, but if we conservatively apply a smoothing algorithm with a 1 second window (too long for vertical corrections), we see a peak-to-peak variation also around 5 Pa. In other words the barometer is able to detect vertical displacements of around 0.5 meters in optimum conditions.

All of which clearly indicates that displacements up or down of a couple of centimeters are not going to be detected on any reasonable time scale by the barometer.
 
Sure. The MEMS sensor article linked above gives a typical relative accuracy, which amounts to around 0.7 meters vertical. Or you could look at the raw pressure data from a DJI aircraft - below is the pressure, in Pa, for a stationary Mavic Pro as the pressure sensor warms up.

View attachment 109112

A couple of things to note. Ignoring the change from start to finish, which amounts to around 60 Pa (equivalent to around 6 m vertical displacement), we can instead consider the higher frequency stability of the pressure reading. For a typical 10 second window the standard deviation is around 5 Pa, equivalent to around 0.5 meters. The noise amplitude is 10 times that, but if we conservatively apply a smoothing algorithm with a 1 second window (too long for vertical corrections), we see a peak-to-peak variation also around 5 Pa. In other words the barometer is able to detect vertical displacements of around 0.5 meters in optimum conditions.

All of which clearly indicates that displacements up or down of a couple of centimeters are not going to be detected on any reasonable time scale by the barometer.
Thank you. I didn't see the article link. Good tech stuff.
 
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?
 
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
 
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
The barometer is not relied on for landing, it can’t be. An optimistic performance spec for a device iof the type currently used in sUAS is accuracy of +/-0.08 hPa. That’s +/- .66m.
 
The barometer is not relied on for landing, it can’t be. An optimistic performance spec for a device iof the type currently used in sUAS is accuracy of +/-0.08 hPa. That’s +/- .66m.

I think it is used for establishing that the aircraft has landed - hence the 3 second delay. It is able to determine a lack of descent over that period. However, I doubt that's the only sensor that it is checking.
 

Members online

No members online now.

Forum statistics

Threads
143,153
Messages
1,468,001
Members
105,051
Latest member
stovesparesdirectuk