Arduino Based Weather Station

[Dave_D]

have you tried the neodymium magnets out of an old harddrive?

[Gina]

No, hadn't thought of that.

[Gina]

Here is the latest design.  Not to scale.

 

Edited December 3, 2017 by Gina

[Stub Mandrel]

You could try opposed disc magnets either side of the disc, although they will attract each other strongly, three pairs could be used to hold the two halves of the box together!

[Gina]

Thanks - yes, I thought of opposed magnets either side of the disc and would probably work without the U shaped iron part.  Hadn't thought of using magnets to hold the box together though.

[Gina]

The cylindrical magnets are a pair of identical ones so both the same pole on the countersunk side.  But a pair of flat bar type which have each pole on opposite sides of the flat sides could be mounted in a 3D printed holder to hold them apart.  If they were a tight fit in the plastic they might stay put as in the first diagram but if loose might come out and join up.  The second diagram shows a solution - holding them fully.

[Gina]

Ordered some flat/bar magnets bigger than the ones I already have - due to arrive tomorrow :-

4Pcs Strong Neodymium Bar Magnets, Rectangular Block Neodymium Magnets, DIY, Building, Scientific, Craft, and Office Magnets-60 x 10 x 5 mm

The 4" aluminium discs are due to arrive Wednesday or Thursday.

[Gina]

If I find it could do with greater damping I could possibly use both discs and three magnets.

[Gina]

Don't think there's much more I want to do to this until the aluminium discs come or at least the bigger magnets.

This is the latest idea of how it might all look.

Edited December 5, 2017 by Gina

[Gina]

Magnets and optical sensors have been delivered.  I've tried the magnets on the aluminium disc I already have and the drag is good with two magnets separated by the three plastic separators so that one half of each magnet works on each side on the disc.  However, I may not use the optical sensors as I'm considering the MLX90316 Rotary Position Sensor IC which gives a highly accurate rotation angle with just a magnet on the end of the wind vane shaft and which is easily interfaced with the Arduino.

[Gina]

Yes, now decided to use the MLX90316 chip and a 6mm diameter x 4mm thick disc magnet with poles along the diagonal attached to the end of the wind vane axle.  Three wires for SPI data plus Gnd and +5v connected to an Arduino Nano and one data wire plus Gnd and +5v (or +13.8v) to the Hall sensor in the anemometer.   I'll probably put the Arduino in the wind sensors casing and connect to the RPi in the ASC via RxD/TxD or possibly USB.

Edited December 6, 2017 by Gina

[Gina]

Tracked package containing MLX chips and delivery is scheduled for Friday by FedEx.  Reason for cost of delivery and time taken is that they are coming from the USA - Memphis, Tennessee!  I would have thought that Mouser UK would have UK stock when they said items were in stock!

Edited December 6, 2017 by Gina

[Gina]

I'm not waiting for the chip making some parts starting with the wind vane.

[MarkyD]

1 hour ago, Gina said:

Tracked package containing MLX chips and delivery is scheduled for Friday by FedEx.  Reason for cost of delivery and time taken is that they are coming from the USA - Memphis, Tennessee!  I would have thought that Mouser UK would have UK stock when they said items were in stock!

Never had a problem with Mouser deliveries.  Usually arrives within 2 or 3 days with import duty & VAT taken care of.  All of their stuff comes from the US I believe

[Gina]

The wind vane print was not perfect - the vane is slightly concave.  It also weighs more than I'd like - 1.8g whereas the thin acrylic sheet from the old one weighs 0.8g.    The vane itself is 1mm thick.  I think I'll see if I have any thin acrylic sheet - generally used for packaging.

[angryowl]

I wouldn't worry so much about the weight. Mine weighs roughly 30g for the vane itself plus 80g for the casing and then the M6 rod which weighs the most. Add to that the tip with the counterweights inside, and the sleeving on the rod and you end up with a fairly heavy vane.

There's some intentional slack in the way my two bearings were mounted to ensure the vane is sensitive enough to pick up even a light breeze.

I don't yet have an anemometer to measure the minimum speed at which it starts spinning but I can tell you that it's REALLY sensitive and even my smallest fan sets it off!

[Gina]

I may yet find some packaging as I clear up though I have chucked most of it out.  But I have found a sheet of slightly thicker acrylic that came with the frame I used for the Moon Phase Clock and not wanted for that so I've cut a piece same size as the printed vane.  Broke printed vane off its bar and weighed both and they're the same weight (11g) but at least the acrylic is flat

[Gina]

I have some strips of sheet lead and have rolled up a piece of about 2" x 1" into a cylinder just over 9mm diameter.  This weighs 27g.  With the C-of-G of the vane 130mm from the pivot the C-of-G of the weight will want to be 130x11/27 = 53mm.  The weight chamber will have  a dome shaped plug to go in the end.

[Gina]

Wind vane arm printed and vane added.  Balance is fine   Now to design and print the nosepiece.

Edited December 6, 2017 by Gina

[Gina]

Nosepiece designed and now printing.

[Gina]

Bit tricky to print.  May be better as just a hemisphere.

[Gina]

New design printed fine, glued onto arm and tidied up.  Looks nice   Not that anybody will be able to tell at 6m above the ground

[Gina]

I'm not sure I shall bother with damping after all as I could apply smoothing in the Arduino sketch or in further data processing in the base station software.  There are several techniques I could use.  I can always see how it goes and redesign and reprint if needed.  That's the advantage of 3D printing  

I was going to use two ball bearings on the axle but I'm not sure it's necessary with a balanced system.  I'm only using one on the anemometer and that's fine.  I'm thinking 5x10x5mm for the bearing.  Or maybe 6x17x6mm.  The smaller bearing has lower friction.

[Gina]

[tekkydave]

My raw wind data is all over the place but I do some consensus processing in the back-end to smooth it out.