Good. I still had fun.

There is even a gentleman who helps me, and who made me a nice drawing:

We see our Pioupiou, its propeller, and ball bearings.

(You can also see other things, like too much leverage between the bearing and the propeller. But since I can't draw so well, I'm keeping this image there.)

Brief. There is in particular the pivot of the propeller. This is THE critical point of our Pioupiou. It will have to do tens of billions of turns. It must therefore be sufficiently robust, including in aggressive environments. (sea air…)

But at the same time, our propeller must be able to turn at the slightest breath. We want to be able to measure wind speeds of less than 5 km/h. It is therefore necessary to have a robust bearing, but which does not interfere with the rotation.

Mission 0 friction

Brief. I played a new game. It's called the " tribology ».

« Tribe- » as from the ancient Greek which means « scrub », and « -logie » like all the stuff we study at school.

We had to find a bearing that did not rub too much. There, two solutions: do math, or do less math. And since I didn't really know how to do the math, I chose the experimental method.

Fortunately, last week, I had exploded the ceiling of my credit card. Among the multitude of things I had bought, there was a small stock of bearings:

 

So to study them, I started by playing with the 3D printer:

To make two funny objects:

The thing on the right is a support. I fit the bearing to test.

The thing on the left is a sort of graduated ruler, which also fits into the bearing.

In short, it's a kind of balance. Here is the result:

After a few strokes with the cutters to adjust the balance, the bar holds exactly horizontal.

Then the game is simple:

We put (very small) magnets, and we move them to gradually increase the lever arm. When it rocks, it means that the weight exerted by the magnet is greater than the friction of the bearing. By multiplying the mass of the magnet by the distance, we obtain the friction torque of the bearing.

It is an approximate measurement, but which allows to have orders of magnitude for the different types of bearings. For example, my bearings " nus » had a friction of less than 0,000001 Nm While a bad sealed bearing had a friction of 0,0005 Nm It's not much, but it's still 500 times more!

Everything-proof

The bearings " sealed are good, but they are expensive in friction. This is because there is a rubber disc that presses on both sides.

We can therefore have a more reactive anemo, by putting a bearing that is a little less tight.

Left: waterproof. Right: a little less watertight.

But suddenly, it is more necessary to protect it against dust and water. But we can probably work it out. For example with a kind of "gutter" that guards the entrance:

It's time to eat. I will stop there for this week. Otherwise there will be no more raclette. And since we've just found an apartment at La Terrasse, it's not the right time to divorce.

See you soon !