Receiving and Estimator Problem V2

Topics related to the Lighthouse positioning system, configuration and use
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sAz
Beginner
Posts: 27
Joined: Wed Jun 10, 2020 5:35 pm

Receiving and Estimator Problem V2

Post by sAz »

Hi everybody,

I am using two V2 basestations for the first time. I tried to set up everything, and I could set the channels for the base stations. Now I am trying to let a crazyflie fly with the V2 system, but I have the following problem.

Screenshot from client.mp4 - 6.png
Screenshot from client.mp4 - 7.png
These are screenshots from a video. As you can see, the colors for the Estimator and Receiving keep changing and never remain on green.

On the quad it looks like this
Screenshot from drone.mp4 - 1.png
Screenshot from drone.mp4.png
I have tried this on different Crazyflies and different lighthouse decks.

I am using:

Ubuntu 16.04, 18.04
The newest version of the client (installed days ago)
The newest cflib (installed days ago)
Python3
Firmware (2021.03)
New Lighthouse base stations

Thanks!
sAz
Beginner
Posts: 27
Joined: Wed Jun 10, 2020 5:35 pm

Re: Receiving and Estimator Problem V2

Post by sAz »

I also have the V1 bassestations. On them everything works fine.
kristoffer
Bitcraze
Posts: 630
Joined: Tue Jun 30, 2015 7:47 am

Re: Receiving and Estimator Problem V2

Post by kristoffer »

It sounds like there is some problem receiving the base stations.

How long are the base stations green and red?

What happens if you hold the Crazyflie up towards one of the base stations so that the other base station is not visible from the Crazyflie? Is that base station stable on green in the client?
sAz
Beginner
Posts: 27
Joined: Wed Jun 10, 2020 5:35 pm

Re: Receiving and Estimator Problem V2

Post by sAz »

In regard to your first question, I have two videos in this link https://github.com/sAz-G/open_folder.

In summary, the base stations remain mostly on green, and they change to red roughly every 5-6 seconds. They remain on red for <1s and then back to green for longer time. So it could look like the following: 5s green, 1s red, 5s green, 1s red, 5s green, 1s red.

Sometimes only one base changes to red and the other one stays on green: 5s green (b1, b2) , 1s red (b1), 5s green (b1, b2), 1s red (b2), 5s green(b1, b2) , 1s red (b1, b2).

In regard to the second question, I will try it first and let you know.
kristoffer
Bitcraze
Posts: 630
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Re: Receiving and Estimator Problem V2

Post by kristoffer »

I looked at your video of the client and this behaviour is actually what is expected, I will try to explain what is happening and why V1 looks different.

In Lighthouse V1 the two base stations are synchronized (either optically or by a cable). The result is that the rotors in the two base stations are spinning exactly at the same rate and with a know phase in relation to each other. This means that the light sweeps from base station 1 and 2 will never collide, first there is a sweep from BS1 and after that from BS2 and so on. This also puts a hard limit of 2 base stations on the system.

In Lighthouse V2 Valve has chosen a different approach and there is no synchronization between base stations. When light sweeps from two base stations hit a sensor on the Crazyflie at the same time, the data is messed up and it is not possible to use the sweep for positioning so it is important to minimize this event and to make sure it is not happening at the same point in space all the time. The solution is to make sure the base stations run at slightly different frequencies (around 50 Hz, based on the channel) which makes the interference point mover around in time and space.

This is what you see when the reception goes red for a bit, the sweeps from the two base stations interfere. If you turn off one of the base stations the remaining one should stay green all the time.

It is not necessary to have reception all the time to fly, the Crazyflie can handle short gaps using other sensor data.
kristoffer
Bitcraze
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Re: Receiving and Estimator Problem V2

Post by kristoffer »

Also, can you fly with the V2 base stations?
sAz
Beginner
Posts: 27
Joined: Wed Jun 10, 2020 5:35 pm

Re: Receiving and Estimator Problem V2

Post by sAz »

Yes, I can fly, but the flight using the V1 is more stable. Also, sometimes the calibration tabs are not green (sometimes blue, sometimes red) and I have to restart the system and try again.

Thanks for the detailed explanation! I would like to try flying using 4 base stations to see if the flight is better. According to the explanation, the signals interfere when there are two or more base stations, does this mean that with more base stations, there is more interference (since there are more signals)?
kristoffer
Bitcraze
Posts: 630
Joined: Tue Jun 30, 2015 7:47 am

Re: Receiving and Estimator Problem V2

Post by kristoffer »

Yes, more base stations creates more interference and will probably not improve the situation. More base stations can be used to extend the flight area but will not help in one point.

For the calibration the meaning of the colours are:
red = no calibration data
blue = calibration data is read from the CF memory
orange = calibration data has been received from the base station but did not match what was red from memory. The new calibration data has been saved to the CF memory but you have to estimate the base station geometry again.
green = calibration data has been received from the base station and match what was red from memory - all is good
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