Display fun

 Acroduster, Arduino, CNC  Comments Off on Display fun
Jul 022020
 

I wanted to use this nifty little display for my RPM display of the spindle on the CNC-Router. It somehow switched to a 128*32 mode.

Digging in the code, I found a problem (for me, in this sketch) Activating the 128*64 define in Adafruit_SSD1306.h library, fixed it.

Yes, of course, it (they) will go into the plane as well, that’s why I got them 😉

/*!
 * @file Adafruit_SSD1306.h
  * This is part of for Adafruit's SSD1306 library for monochrome
 * OLED displays: http://www.adafruit.com/category/63_98
 * Written by Limor Fried/Ladyada for Adafruit Industries,
 */

#ifndef _Adafruit_SSD1306_H_
#define _Adafruit_SSD1306_H_

// Note: my display only showed 32 lines, 
// changing this define to the one below
// cured the problem. Standard 'define SSD1306_128_32' is wrong. 
// Kees Blokland, 2 July 2020

// ONE of the following three lines must be #defined:
#define SSD1306_128_64
//#define SSD1306_128_32

Update: The better and proper way is to add the directives from the updated library in the source code:

Adafruit_SSD1306 display(128, 64, &Wire, 4); // This forces 128*64 display and a reset. Before it was:

Adafruit_SSD1306 display(4);

So the display is working, but values are jumping around too much. This is a known arduino limitation, and somewhere I have a library from ElectricRCAircraftGuy that solves the problem to a large extend.

Oh, and in the meantime the router motor has decided to stop. It did sound funny lately, more work! Usual case of ‘last night it worked, today it does not’. Using a Dremel for creating revolutions to count.

Yes the shed roof is still being worked on too, and so is the garden, and a myriad of urgent stuff…

tip-work

 Acroduster  Comments Off on tip-work
Jun 282020
 
Lower wing as it should be..

After glueing the trailing edge wood (not shaped to final yet!) it was time to do a bit of tube-bending. It’s 4 mm tube, and for the life of me, I don’t know why it is so soft. Almost feels like copper tubing. Never mind, just try to match the shape.

bend wood and bend tube

Trying to hold the camera at just the right distance and level is probably easy if you were to create a support. Maybe one day? I just needed to get the tip shape lined up with the trailing edge, and make sure the lines ‘flow’.

A quick copy paste on the original drawing makes it look close enough. There is some distortion in the camera, the rib distances are correct.

Good enough to carry on!

it matches well enough.

In the meantime I’m making more ribs, more trailing edges, more of everything. But that has all been documented, I’m not repeating it 😉

when metal meets wood..

 Acroduster  Comments Off on when metal meets wood..
Jun 192020
 

Making sure wing mates with the fuselage.. And a single 3.18mm pin does secure it to the fuse.

Not much to say, just wanted to see how it looks. After this pic was taken, I glued in a bunch of false nose ribs.

there’s no way back..

 Acroduster  Comments Off on there’s no way back..
Jun 182020
 
ribs glued to the spars

The ribs trimmed to size (sort of) Even at this stage the wing is very stiff. Normally in a balsa/built up wing, it is pretty easy to twist the structure. Due to the way the ribs are built, there is an decent amount of torsional stiffness, even at this stage. Next I have to make the root rib and tips ribs.

Next maybe the aileron, since that takes quite a bit of additional mechanical work. The TE can be added as the last bit. so that there is a nice curve along the ribs.

I’m still thinking about the tubular bracing in the wings. I don’t really need it. If I change my mind I can add it at the end. I will save quite a bit of weight, is there just ”because the original has it”. The leading edge covering will provide enough for-aft stiffness.

For my own reference: ribs are slightly under 10 grams before trimming to length. The whole wing at this stage is 335 gram, that’s including some metal. What the target weight is? No idea to be honest, I would think around 700-800 gram all ready. But up to a kilo for each wing will be ok, I need the weight!

it’s getting serious now..

 Acroduster  Comments Off on it’s getting serious now..
Jun 162020
 
around 40 ribs cut, and 10 glued up
looking ribly..

A good day was had, is the saying. Over the last week or so I have been bending the cap-strips. It is a time consuming job. First you soak them for a few days, then clamp them in a jig, then let dry for at least 24 hours. Repeat.

Since there are always minor variations in the construction, my plan is to route the outline to final shape once I have enough ribs done. That would make them all exactly the same, which is the whole purpose of all this effort.

Another day, another rib..

test fit one more time.

more rib testing

 Acroduster  Comments Off on more rib testing
Jun 062020
 

If in doubt do it the Paolo way 😉 . Success guaranteed!

cap-strips added

The full size cap-strips for the ribs are 1/4 x 1/4 pine. Scaled down that translates to 2.12 mm square. That is just too small for my fingers.

The plywood I have (that lite-ply) is 2 mm. I have nice 2 mm mill bits. (Not great for wood, but it works). Some time later, I have found The Way to Do it.

Mill a groove in the 11 mm strip, offset from centre (don’t ask where I got 11 mm, that’s what it is, came from some “Imperial” country. Supposed to be 1/2″), turn it around, same again, and last, run a deeper groove in the centre to cut it into 2 halves. Bingo, nice cap-strips.

Next I probably need to make a jig so I can glue the cap-strips on the ribs. (40 odd ribs.) en in general get busy. Once the glue dries, I can (if needed) sand the cap-strips down a bit, looking for no more then 3 mm wide. I’ll leave the height for now as is, it will give me some room to play with during the final assembly.

The vertical rib stiffeners are just scrap, probably do them in thinner ply. Joining the mains and aft spar requires triangular pine blocks, again, by the time you scale things down, they are small. I think I have a cone bit somewhere, I will try to make the blocks the same way as the cap-strips, mill a groove and chamfer the side..

Ouch, almost got myself in trouble. The cap-strips run all the way from LE to TE !! Even though the nose section of the wing is covered with plywood! Good to check, and check again. Which means I have to make the ribs complete, and slide them over the spars. No problem, but it shows you got to pay attention.

2 mm grooved cap-strips, can be sanded to size once glued to ribs.

making ribs

 Acroduster  Comments Off on making ribs
Jun 052020
 
trial wing ribs.

With the wing spars ready, it’s time to start thinking about the ribs. On these wings, nothing is straightforward, every rib looks different. (which gives it those nice wings 😉

Luckily the designer was smart enough to keep all the ribs up to the aft spar the same, so the only difference is the rear section of each rib. Which means, after I sorted the profile, I decided to make some test ribs to see how it all looks.

These are really just for testing, the wood is something called lite-ply, which to be honest is pretty useless. It’s as light as balsa, but warps by just looking at it. Been carrying it around for 20 years, so time to get rid of it!

The profile is approx 13%, I might thin it down slightly, I think 12% will still fit. It’s roughly a NACA0013, so 12 will do just fine. Or 12.6, or something.. I’ll think about it. Have to make sure the servo’s fit as well!

more small steps..

 Acroduster  Comments Off on more small steps..
Jun 042020
 
exactly 6 degrees bevel.

At some stage, after laminating the wing spars, I needed to bevel them at 4 degrees for the forward, and 6 degrees for the aft spars. Could have done it by hand, but this was quicker. (After spending 2 hours thinking about it, and trying to mount the planer. ) Only do this under adult supervision. You’ve been warned. Count fingers. Keep them.

Anyway, looks good. The main spars cut to length came at 97 grams each. That’s the great thing about wood, if it is too heavy, sand some more, until you get to your target.

Adult supervision required.
Lower wing attachment points.
starting to look like a bird…

There are some small errors in the laser-cut parts, but nothing that I can’t fix quickly. If I remember right, at one stage I thought that I needed a bit more material around holes, so added 0,5mm to the outer contour. Should not have done that, stuff is strong enough as it is! The rear attachment point is now a bit tight, but as I said, easily fixed.

Nothing like a good plan..

 Acroduster  Comments Off on Nothing like a good plan..
May 122020
 
..getting the right size and producing lots of shavings to get there.

After many thinking’s and deliberations, I came to the conclusion it would be better to build the bottom wings first. The mounting points are already fixed to the fuse, so their alignment is hardwired into the frame. When the bottom wings are done, I can align the top a bit easier.

I had planned on making the spars from sticks I have saved for 15 years now. They are vintage, but appear to be in good straight shape. These were once destined for a Waco project that never took off. There’s enough of them, and laminating thin strips gives a nice strong spar. Rear one is approx 26 x 7mm.

even a simple straight spar is not that simple!

I hope that having wings will make other parts easier. (famous last words.) The wing structure is going to be per full size, the hard way. The spars are what carries everything, and fore/aft stiffness is provided by 1″ alu tubing. The stuff that would be available is actually heavier then stainless steel, so I am going to use that. Which means I also need to make brackets for those tubes. And when I am at it, do all the other bits I need as well.

Glueing strips together is not that exiting, but this is the result.

seems the random alignment did not work out. Pay attention young man!

And for the rest, a bit of sanding and shaving to get to the correct size. I love the smell of pine!

Back to building

 Acroduster  Comments Off on Back to building
May 012020
 

I got a nice envelope of Bling last week. The process of getting from the parts I drew to something in my hands is not that complicated. Submit a dxf file, receive a quote, say yes, wait a few days, done. And the good part is, it is not breaking the bank!

The one thing that I had to learn is that a ‘part’ is a single dxf file. What you see here is a single file. Why is this important? The handling and preparation fees deal with single parts. There appears to be no limit to how complicated the parts is (apart from obviously the amount of time the laser needs to cut).

To keep it simple, stick as many individual bits together as you can, to produce as large a part as possible. That gives you the cheapest part. Unless of course you want a 1000 of each individual bit, but then we talk something else.

All I had to do is cut the bits apart, do a bit of filing and sanding an you’re done.

nice little puzzle

So next is doing some trial fitting, and start building the center section of the top wing. Once that is done, the cabane structure etc. At the moment there is a build thread on biplane forum, at just about the right stage. I’ll add some of these here for comparison

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