# How is position tracked?

How is kite position in the wind window tracked by the different kite power companies systems? What is the most popular method, and what are the advantages, and disadvantages of the different tracking systems?

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At Kitemill we currently use a quite good GPS based system. We went through many units that did not handle the high G forces during loops. I am not at liberty to share the exact model we are using unfortunately.

We dont use any tether sensor, though this is perhaps not the final picture. Tether sensors at the ground have the problem that tethers are curved, so you dont get an accurate reading unless you add a sophisticated algorithm.

In addition of course we know the length of the tether with some accuracy, though this information is a bit redundant once we know the GPS location of the kite (the location of our pulley is known a priori)

Problems with GPS systems is finding the attitude. You can use an accelerometer to find Â«upÂ» but to find the initial Â«yawÂ» you need a compass or something else to the same effect. A compass is not a very accurate way to determine yaw unfortunately.

Eyeball
Lift kite is hanging over a bit hmmm itâ€™s a bit too left then.
There was one team (Ampyx?) Moving towards using a network of small location sensors across the field and a couple on the kite for faster more reliable sensingâ€¦ Darn whatâ€™s the tech called againâ€¦

I thought there was a rough hight position in the GPS data? And to get more accurate you can use a barometer on the kite, and one on the ground station and compare the two readings. The difference will be the kite height. And for the pitch/roll/yaw there is some really cheap 9 axis IMU chipâ€™s.

You have the length reeled out and tether weight per meter, and with a loadcell you have the pulling force, and with a anemometer you get the wind loading on the tether. I am sure you can get some math genius at the cybernetics department at NTNU to give you an algorithm for â€śtether bendâ€ť in just a few minutes with those factors available.

I guess you might be referring to me, but I am far from a genius, just another person. Still, I did try to describe the curvature at:

https://www.researchgate.net/publication/336617086_THE_SECOND_MOST_IMPORTANT_LAW_OF_TETHER_SCALING

Still, the solution GPS/INS solves our need for navigations right now without any additional R&D, and we have plenty other things to focus on right now.

For sure, there is room for improvement. In particular, GPS is weak against jamming and spoofing. So a radioless backup solution may be necessary.

Another approach which may be good for an emergency case where GPS is not working, is to stabilize the kite and then just reel in the tether. The kite will eventually end up at the pulleyâ€¦

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