Motion Estimation for Tethered Airfoils with Tether Sag

There’s a paper here on Motion Estimation for Tethered Airfoils with Tether Sag
by * Jan Hendrik Freter

Very handy for all the Yo-Yo fans
The conclusion reads as…

We have considered the problem of estimating the position
of tethered airfoils from tether angle measurements and IMU
data, whereby we focused on the effect of tether sag on
the position. We proposed a novel method that adaptively
weights between the tether angles and the IMU data accord
ing to the tether force. In comparison to a state-of-the-art KF,
the developed fusion method has demonstrated to converge
signifificantly faster on simulated and experimental data and
has led to an improved accuracy. The method assures that
the tether angles are trusted whenever they are known to
be reliable. Furthermore, the method uses the IMU data to
overcome the periods when sagging occurs and the tether
angles are unreliable. However, the experimental data only
provides a proof of concept and a detailed validation study
with an accepted ground-truth measurement will be subject
of future research.
We conclude that the developed method allows the user to
increase the position estimation performance for tethered air
foils regarding the accuracy. Moreover, we provide a solution
that is independent from camera data and is not restricted by
weather or light conditions. The proposed method uses low
cost IMUs and can be applied for the systematic testing of
sport kites as well as for AWESs.

1 Like


Im going to be a bit bullyish here.

I believe the best solutions dont require the ground station and the kite to communicate. This is mostly from a robustness perspective. So I would prefer a IMU GPS solution to anything measuring the tether angle at the ground. The only exception of course is if the kite controller is at the ground (multiple tethers for steering).

For most practical purposes what we have at Kitemill works well and is simple and relatively cheap to implement.

Now I also dont really like that we are still depending on a radio link to the GPS satellites. I believe that we could also do away with the GPS if need be. There are a few other sensors options that could be used to figure out an accurate position and orientation.

If communication with the ground station is important, I think one would need a robust solution, and I believe communicating with sound waves on the tether is the most viable solution. Oil drilling does similar stuff by sending sound through the mud, to get sensor telemetry and steer directional drilling (I believe thats some things they use it for)

More info Measurement while drilling - Wikipedia

That being said, the paper is very nice, though the accuract must be further improved to serve practical purposes.

1 Like