Mechanically fixing three axes on a hard disk rotative part

Hi all.

I want to build an anemometer based on Hall-effect sensor, and now after three days I finally understood that wiring correctly the sensor improves vastly his reliability, so I can start working on the rest of the project.

And that's where I'm stuck: how to fix three axes on the hard disk rotative part ("palier" in French) that I plan to use?
Like this, I mean:

Note that the design shown here uses a computer fan, but I've been told that it's not frictionless, and a hard disk rotative part would be better (the author of this design notes that it's not reliable with slow wind).

There are screw holes on the top of the HDRP, but the difficulty is to keep the design as light as it can be, in order to be able to detect weak winds...

It will be important to get the cups equally spaced. That might be easier with 4 cups.

Can you make a small disk with 3 holes (one for each arm) which you can glue to the top of the spindle? Perhaps from a piece of wooden dowel?

What about cutting a triangle from a piece of aluminium and screwing the arms at each point?

I would not worry too much about weight as long as it is carefully balanced.