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[RESOLVED] TWR to TDoA2 Mode Failure

Posted: Tue Jan 15, 2019 10:06 pm
by HuzayfaaN
Hi All,

I am struggling to switch from the TWR mode to the TDoA2 mode using the cfclient and following a tutorial.

I have one CF and 6 LPS Nodes currently set up in the TWR mode, following the 6 anchor reference setup as suggested in the 'Getting started with the Loco Positioning system' [1] tutorial. I have successfully been able to set-up and configure the 6 LPS nodes and execute controlled flight (using a game pad) in the TWR mode - following the setup below.


However, when following the steps of 'Switching system mode to TDoA', as part of the same to tutorial [1], I have issues and the CF no longer acknowledges the 6 LPS nodes once the switch has completed. When following the steps as part of the section 'Switching system mode to TDoA', it all goes well (as far as I believe and understand), until the part when switching the CF back to auto mode to confirm the TDoA mode. When switching the CF back to auto mode the green boxes on the right of the modes light up in sequence (one after another as the CF is trying to determine what mode it is in). It does this for a while and the LPS node anchor boxes all remain red and therefore I do not accomplish this step as part of the tutorial [1]: 'The anchor boxes should also turn green when the CF switches to TDoA mode and starts to receive data from the anchors.'

[Q1] Is there another way I can attempt to set-up and configure the 6 LPS nodes + the CF in the TDoA mode? or can we investigate what is going wrong and what I may be doing incorrectly?

[Q2] Does the TDoA mode work with 6 nodes or is it a requirement to have 8 nodes?

Any help and suggestions would be highly appreciated. Thanks in advance!

Lastly, I am able to (using the windows LPS Tools software) reset the nodes back to TWR and give them ID numbers and then go back to TWR in the cfclient and that all works fine and as expected.


[1] Tutorial Link - ... m/#intro26

Re: TWR to TDoA2 Mode Failure

Posted: Wed Jan 16, 2019 9:11 am
by arnaud

First of all, you should check that you have the latest firmware version both in the Crazyflie and in the LPS nodes. When switching mode it is normal that all anchor goes 'red', but they should re-appear when you switch the Crazyflie to the new mode.

[A1]: Yes you can set the TDoA mode in the LPS tools software. TDoA2 requires anchor 0 to be present and visible from everyone (anchor 0 is the master orchestrating all communication). You can also try TDoA3.

[A2]: TDoA works best when the Crazyflie is within the anchor convex hull. With 6 anchors it is a bit hard to get a nice convex hull but it should anyway work. You might just have to elevate a bit the Crazyflie at startup to have the position lock when they are in the convex hull, during flight the kalman filter is normally able to keep the position estimate OK even when going slightly out of the convex hull. If you have decks like the flow or the Z-ranger, is can help a lot flying in a TDoA system with less anchor since it will give to the EKF an accurate height estimate.

Re: TWR to TDoA2 Mode Failure

Posted: Thu Jan 17, 2019 10:31 pm
by HuzayfaaN
Hi Arnaud,

Thanks for the reply and answers to the questions raised.

I had my anchors numbered between the ranges 1 and 6, which once I correct to 0 to 5 fixed the issue I was having. I am now able to successfully switch between all modes (TWR, TDoA2 and TDoA3) using the cfclient.

And I'll definitely attempt using a flow/z-ranger to help achieve a more accurate height flight with TDoA.

Thanks Again! :)