Nasa masthead anemometer

[PaulGS]

Is there anyone out there who's taken apart the anemometer on one of these units? Examining my unit, the anemometer cups seemed to hanging very loosely on their spindle and displaying a lot of play. When I took the cups off the spindle I found that the internal diameter of the metal anemometer 'sleeve' was much greater than the internal diameter of the spindle from which it hangs - I wondered if there should have been some sort of bush (now missing) between the two surfaces? (Let's not bother with the usual expressions of disgust re. the longevity of Nasa products eh?)

 

[neil_s]

Sorry - not sure where you are finding wear in your anemometer cups. If it's in the cups bearing, replacement cups are easily available from NASA and others. I have not seen a detachable metal sleeve - I think they are all plastic. I have an early 5 wire NASA Wind where the spindles are cast into the plastic mouldings. If the spindle has come loose in the plastic moulding, it is possible to remove it by careful drilling from the inside surface of the moulding (anemometer needs to be disassembled first!) and then a new spindle glued in place with epoxy. If your old spindle is not worn, then it could be re-used, but I found mine had been eroded by the little spacing washers NASA provide.

 

[B27]

Yes, I think there should be a plastic bush in there.
I bought a new direction vane, ISTR the instructions which came with it showed the wind cups too, and there were variations on bushes, washers and such.
I was able to machine a brass bush for mine and it works now!
The fixed stainless spindle is also obviously worn, and no longer parallel.
The cups had been hitting the housing and wearing it!

To be fair, I think mine is more than ten years old and I've seen plenty of failed stuff from more expensive brands.

 

[PaulGS]

Yes, I think there should be a plastic bush in there.
I bought a new direction vane, ISTR the instructions which came with it showed the wind cups too, and there were variations on bushes, washers and such.
I was able to machine a brass bush for mine and it works now!
The fixed stainless spindle is also obviously worn, and no longer parallel.
The cups had been hitting the housing and wearing it!

To be fair, I think mine is more than ten years old and I've seen plenty of failed stuff from more expensive brands.

You seem to have an intimate knowledge of the unit so I wonder if you can answer another technical query? The cup unit has a small piece of metal embedded in its upper surface - this presumably what 'triggers' the sensor in the main body of the apparatus above it. This piece of metal is rusted and flat - but there's a concave ring above it in the main unit suggestive that it would originally have been raised and revolved within that ring - am I correct?

 

[B27]

There are two distinct models of Nasa wind instrument.
Mine is '5 wire'

The vanes and cup units are different
Wind Anemometer Cup Kit - Nasa Marine Instruments

In the image in the link you can see a little magnet. Pretty sure mine was actually fully buried in the plastic.
Basically there's a small IC Hall Effect sensor which senses the changing magnetic field every rev.
On mine, that sensor is in a 'well' (was full of water!) at the bottom of the body, so the boss of the cup unit surrounds it

It sounds like yours may be a 3 wire unit.
The only metal embedded in the main body of mine is the two spindles. And the mounting tube.

The assembly instructions I have show washers above and below the cup rotor.

I might speculate that your rusty ring of metal could be there to improve isolation between the speed and direction sensors?
The 'tactical' display probably needs more sensitivity than the simple old 'direction to the nearest 5 degrees' or whatever.

The vane on mine had a rusty ring at the bottom of the vane's boss, This is weakly magnetic, I had to renew the vane to make the direction work.

Or maybe your unit has suffered some DIY maintenance in the past and the rusty ring is a washer that's been added to take up the slack?

 

[PaulGS]

It sounds like yours may be a 3 wire unit.

Correct. But I seem to have confused you - it's my magnet that's rusted. The 'ring' is a concave groove mirroring the circular track of the magnet. Thank you for your input.

 

[B27]

Correct. But I seem to have confused you - it's my magnet that's rusted. The 'ring' is a concave groove mirroring the circular track of the magnet. Thank you for your input.

As in just rust-stained plastic?

If you can get rid if the slack, so the cup rotor doesn't wobble, it may still work.
Might be worth splurging £20 for a new cup rotor, rather than trying to prevent the magnet rusting any more?

 

[kwb78]

They are quite a simple design. They don't have a bearing, just a spindle that is on the unit, and a bush in the cups, held on with a very small nut. This bush in the cups wears larger over time making the cups a looser fit. Eventually they fail and can fall off. Sometimes the spindle can get damaged and need replacing. NASA will normally do this for you at a very reasonable cost if you return it to them.

 

[PaulGS]

They are quite a simple design. They don't have a bearing, just a spindle that is on the unit, and a bush in the cups, held on with a very small nut. This bush in the cups wears larger over time making the cups a looser fit. Eventually they fail and can fall off. Sometimes the spindle can get damaged and need replacing. NASA will normally do this for you at a very reasonable cost if you return it to them.

You're quite right. The chap who sold me the stuff (wireless, for £100) said the bearing had 'gone' - but it's as you describe. I got it all working earlier today after hooking it up to a car battery, and I'd have had a go at a DIY fix - but the one item missing from the package was the masthead fixings. As these cost a total of nearly £13 to have delivered one might as well go to the additional cost of a new set of anemometer cups for the same all-in delivery cost.