It's the story of a guy, one Friday evening, sitting on his paraglider in a corner of Grenoble station. He missed his train (again!!!), so he's waiting for the next one. And suddenly he takes the opportunity to tell his little story of the week.

You guessed it, the story he is going to tell you is that of Pioupiou.

Like a bit too long intro

Pioupiou, you know him: he's a little bird. It is a small bird which is just beginning to flap its wings, but which soon will have to brave the fierce wind from the top of the mountain.

Brief. Pioupiou, it's a great LEGO game!

Ok. That's a bit of a quick transition. But I don't get paid to make pretty transitions. And anyway, I'm not even paid at all yet. Besides, I work for myself, so I have the right to talk all the nonsense I want. And then damn. So good...

Brief. (I like to say "short")

Pioupiou, it's a great LEGO game!

It's full of little blocks to put together, to make a cool thing at the end. The question is just to know which blocks to assemble? ", and also " how? ».

So let's start with the reviews: last week, I explained to you roughly what shape I wanted to give to the object, and what technologies I wanted to put in it.

But in the end, that was a bit like the story of " I want to build a space shuttle with my LEGOs, and then it will have three reactors ". Let's give this instruction to children, and see how many different space shuttles they will make for us.

Except that we don't want to build a space shuttle out of LEGOs, but rather something like this:

A LEGO weather station stolen from the net

This is starting to get interesting 

So the first question we have to ask ourselves is: what bricks do we have? ».

In fact, there are already plenty of bricks that we already have. As I had already made the first prototypes of Pioupiou this spring, I can reuse a lot of things. The solar, the electronics, the antenna, it is acquired.

It remains to take care of the housing, the propeller and what to put between the two.

I like your plastic

For the box. We now have an approximate shape.

All we need is to know the exact shape of what we are going to put inside. That's exactly the job I do now.

As soon as we have that, we can spend €15 on molds to make the final shape. I'm eager to.

But given the price of the thing, will not crash. Fortunately, I have several plastics experts who offered to help me. And we can do a bit of prototyping first. I'll show you in due time.

You seriously attract me

We had talked of magnets.

The question was: if we put a magnet on the propeller, will it disturb the compass? ". So I pulled out the calculator to check it all out.

In truth, I did not make scholarly calculations. I just found in Google an excel sheet " magnetic field strength calculator ».

Anyway, she gave me the answer I expected: if the magnet is small enough, the magnetic field dissipates quickly. I no longer have the numbers in front of me, but anyway. If we have a 2mm magnet 10cm from the compass, it will not be bothered.

Well, math and theory is good. But I like doing things with my hands. So I ordered lots of small magnets to do real tests. I will have them next week.

Do you feel it well?

So if we have a magnet that borders on the millimeter, we need a fairly sensitive sensor to detect it.

Brief. You know the story: Google…

So I found a sensor based on TMR technology: Tunneled Magneto-Resistance. It's like the famous Giant Magneto-Resistance (GMR) I told you about, but in an even more high-tech version.

The machine is called MMS2X1H. It costs a dollar, draws 1,4 micro-amps, and can detect a tiny magnetic field. It's perfect.

The manufacturer's site is in Chinese, but I was finally able to order a few copies to test. Long live the postman!

It rolls my hen

Once the electronic part is well advanced, it is also necessary to be interested in the mechanics.

The most critical part is going to be the thing that spins the propeller. Imagine: it has to resist in all weathers, with constant wind, for one or more years.

I did all kinds of clever calculations to estimate aging. The upshot is that good quality ball bearings can probably do the trick. The thing that will be lacking in the long run is lubrication. By taking stainless steel, we will limit the damage, but it will probably be necessary to change them from time to time.

My choice fell on nicely named 623-2RS bearings.

« 623 », it means: inner diameter 3mm, outer diameter 10mm, width 4mm. Logical, right?

And the " 2RS ", it means that they are " sealed » : equipped with a rubber side to protect the balls and grease from water and dust.

The interest is that this bearing model is very widespread in the industry. So not only are they not too expensive, but they are also quite easy to find. Practical, therefore, the day we have to replace them. It's the kind of thing you can see in skateboards, remote control cars or even fishing reels.

If it's strong enough for a skateboard, it should go for the propeller of our little Pioupiou.

However, one thing must be validated: check that the sealing rubber does not interfere too much with the rotation. We still want it to turn our propeller! And since I couldn't find the math for that, I ordered loads of bearings to try.

Sorry, I'm getting divorced!

Brief. Next week it's going to be Christmas in the mailbox.

It's going to be Christmas so much, that with all that and last week's 3D printer, I exceeded my credit card payment limit. And there, it was the tragedy. Really.

So I phoned my very (too) dear Banque Postale, to ask them to increase the ceiling on my card for this month. Nothing more normal.

Except that 4 days later, I still couldn't use my card. I even received a charming letter from them: The current situation of your account does not allow you to raise your payment limit »

I believed in an error, because the " current status of my account is still a credit balance of just over €30.

After wasting way too much time on the phone, I was told " that we no longer raise the ceiling on this type of card ". And " you do not have enough seniority with us to have a card with a higher limit ».

In short, I don't have the right to spend my money on work... I find it rather grotesque, since it's an account called " professional ". I do not see how a professional can work with a bank that does not allow him to make card payments.

So rather than waiting a month for my card to be functional again, I preferred to change banks. Like that in a week I have a new card. It is faster.

I still lost two days to find another bank, correct. That too is quite an adventure. Two asked me for a business plan to open an account. I come to deposit money, not to ask for a loan! One of them even asked me for a CV. Suffice to say that I did not insist on them. It's amazing how these banks seem to be 20 years behind.

But in the end, I was recommended Banque Rhône Alpes, a subsidiary of Crédit du Nord. I was able to open an account there without any worries. We'll see what happens in the long term. Anyway, I could have done without all that.

Hopefully next week will be more constructive.