Gina

Bearings decided.  I'm going for an SS ball bearing for the anemometer.

That's cheating!!  Though I have used a similar technique myself!  😁  A craft type hot air gun comes in handy.

Yes, as I understand it making your own actually costs a fair bit more than buying ready made.  OTOH I have never got round to building my own (only looked into it a bit).  There are several members who build their own and they will be able to tell you the costs.

Don't know...

I don't like printing very small stuff either.  I shall have to finish my "GinaRep UltiPrinter" to print really small stuff.  Might get round to it soon...

Brilliant!!

Ah!!  That would explain it - thanks  Wim 😀

I've printed the hub and Rrc comes out at 110mm giving Ar of nearly 2.3.

This is a new (bigger) anemometer, previous one had Rrc of 75mm so 3 magnets for mph was about right.

With the bottom end of Force 1 on the Beaufort Scale being 0.5 m/s it may make sense to use 4 magnets when counting pulses per second.  With three magnets they fitted comfortable between the spokes but two or four don't so I may increase the hub size to accommodate the magnets.  This would bring the Ar value up to 2.  OTOH the tolerances we're discussing here are far less significant than things that interfere with the wind speed.

Another bit says

Quote

Ar = 0.019Rrc + 0.196

So maybe the formula near the end had a misprint!  In my case the above would give about 1.9.  So two magnets on the anemometer would give roughly metres/sec.  Depends whether I want m/s or mph.

Hmm...  A is in metres/sec per Hz so presumably Ar is too.

My Rrc is about 90mm, giving Ar = 1800.  That doesn't make any sense!!  I would expect a value around 1.

I've found

Quote

Ar=20.7Rrc

With Rrc in mm but not found what Ar is in.

PHEW - Ma bwain 'urts Bwian!!!  Just been "reading" the PDF.  I shall need to try to read this again to get the calibration factor for my anemometer.  One thing stood out though - the size of cup made little difference but the radius of cup centre from axle did.  Intuition (or common sense) tells me that bigger buckets/cups should be better at overcoming friction in the bearing.  I wonder if anyone has read this article and boiled it down to basics.  How bucket centre radius relates to calibration.  May go and have a lie down!

37 minutes ago, JamesF said:

Just checked the OWW code and that uses 2.453 for mph, too.

James

Ah, so the value of 3 that I assumed wasn't that far off, but the PDF may give a better value.  I shall be reading it.  Thanks James.

Found the post but it doesn't say how I got the calibration info.

I seem to remember that somehow I estimated that a third of a revolution per second represented 1mph but I'll need to go through my Arduino weather station thread to see if I can find it.

Well done

Generally it's called "Sod's Law".  And I agree entirely!!  Yes, I'll put it where I can take it down for servicing fairly easily.

Actually that bearing ball is 14mm not 12mm.  I see I should also have 9.5mm bearing balls from searching my Amazon purchases.

Hmm...  Two opposing answers about ball size and grease or oil.

If the cavity is filled with grease or oil a SS ball would not be necessary.  I would worry about grease getting stiff when we get frosts.

Another point - if filling the cavity with a light oil I could use a standard 5x10x4mm standard ball bearing I already have though a single bearing ball resting the the hex hole in the bolt head has appeal.  That means the ball turns with the bolt and the ball to flat plate forms the end bearing.

@ChriskeI'll draw a model with the 12mm (or 1/2" ball I already have).

I have steel bearing balls that I used in my Marble Machine of about 12mm diameter.  The current wind vane has a 5mm hole for an M5 bolt and I think I'll try the same with PLA bearings and bearing ball at the bottom with the bolt head resting on the ball and the ball resting on a flat plate (something hard preferably, or maybe PTFE).

OTOH I think those balls are a bit big and they are not stainless.  I think it may be worth buying some smaller stainless steel bearing balls - only a few quid.

What size of bearing ball would you recommend please @Chriske

There are two sites I had in mind for the wind instruments but one I used in the past involves using a ladder to attach the mast to a shed.  The second is on the SE corner of the sun lounge, on the south side of the bungalow, with the bottom of the mast on the ground.  The disadvantage of the second site is that the wind will be partly obstructed by the bungalow from the north.  OTOH wind from this direction is generally less and also less frequently in this quarter.  Most storms come from the SW or SE.  We are sheltered from the NW by rising ground and tall trees.

Checked second position and it's out of sight of the imaging rig.  Also, the mast height is about the same as the roof ridge on the bungalow.

I think I shall use something like that for the wind vane but I was hoping to have the anemometer underneath.  That arrangement will only work for something on the top.  I could have the units side by side rather that one above the other though as in my original design and like the ubiquitous Fine Offset WS.

I agree with that but it mustn't interfere with imaging - ie. be in the FoV available from the mount.

If I can get a reading with a Force 1 - light air, I shall be well satisfied.  That's 1-3mph.  Anything less is Calm anyway.   I get that with nice new ball bearings.  I'm thinking of reading wind speed in integer mph anyway.  Accurate enough.

Do you mean a hole in a PLA part with a stainless steel bolt?  We need very low friction.  Could easily try it though.