Sunday, November 19, 2017

Turbulence at the top of my mast

I installed a little tuft to estimate the amount of turbulence at the top of my mast:

As you can see, it is in view of my video camera. The result of a test run on the freeway is here (and note also impact with a tree branch ... happily no harm done).

Here are some things I noticed:

1. The piece of copper wire holding the tuft in place is a little bit wiggly, which could be exaggerating the movement of the tuft.

2. That said, even when there were few road bumps and the wire was staying put, the tuft was wiggling around quite a bit.

3. It seems difficult to estimate the frequency of the oscillations but I'm going to suspect it's just broad spectrum noise.

4. If this is any indication of what things look like on a crowded runway, I'll have to do some serious digital filtering to basically reject everything except the bandwidth of interest, which is probably no faster than 0.5 Hz or so.

With that in mind, then, the following is my plan of attack:

1. Build up and qualify a reliable new probe.

2. Test it with the 60 mW XBee modules, pushing the sampling rate as high as I possibly can while still getting reliable comms.

3. Thus oversampled, now add a simple lowpass filter on the display.

4. Give myself a TODO item to learn about Kalman filters and implement a more proper filtering strategy later.


  1. I saw you out in the freeway this morning, I'm the black Kia Soul that drives by at 8:25 :) Also I've had a todo item to learn about Kalman filters for about 6 years now but haven't gotten to it.