Kees

3D printer woes..

 Uncategorized  Comments Off on 3D printer woes..
Nov 192020
 

My bed was giving me problems. For ABS you need a bed temperature of at least 100 C. 110 is better. In the original design, all electronics are in the base of the printer, but with a 110 degree bed things were getting too comfy. That resulted in random interruptions of the print, even with added fans in the bottom Since I ran out of PLA and ASA filaments, and only had ABS left, I decided to fix the problem properly. So I stripped everything and rebuild the whole thing. It was only a weeks work, but I am pretty confident things are working better now.

Because I rebuild the bed, it also meant doing all the lovely calibrations from scratch. Anyways, we are back to printing, and at this moment the blinking lights are blinking as they should.

So now I can print a few brackets and bits to finalize the upgrade. Another job done, and hopefully lots of happy ABS parts to come.

Still need to add the camera again, and some interior lights, and a door to keep all the precious heat inside the box, but we’re getting there!

 Posted by at 7:47 pm

Playing with electronics again.

 Uncategorized  Comments Off on Playing with electronics again.
Nov 122020
 

Nothing serious, trying to catch up on some loose ends. One of the fun things I tested today was seeing how low my input voltage can go before the output (5 Volt) collapses.

The background to this is that initially when building Jeti sensors, I used step-down converters to allow the use of 2S battery systems. Some were failing very quickly, and often suffered from brownouts. Therefore I searched for a better solution. Buck-boost converter technology is old hat, just finding suitable ones in a small package was the challenge. I’ve been using these for a while now, with no problems.

In this test I wanted to see how low I could go with the input. As expected, the receiver works to about 3.4Volts, then it complains. The buck-boost converter keeps producing 5 Volt for the sensors, so they are happy.

It’s nice to see that the input range for my Jeti sensors is from 3.4 to 8.4 Volts.

(I should also try if they can handle a DLG. Even 2 if needed. That’s another project.)

buck-boost converter is the red thingy.
need to calibrate the voltages, but it gives you the general idea.

The voltage measured by the Receiver is slightly off, it’s really 3.4 Volts, the measurements for the other inputs are not calibrated yet. I used 10% resistors, so not exactly precision stuff. Will work that out later. This was more about seeing if I kept the 5 volts going. And it does. At least I have a picture to show that now.

 Posted by at 7:51 pm

Change of format

 Acroduster  Comments Off on Change of format
Oct 262020
 

I’m going to make one post a week, and add all the stuff I do in this post. Unless I change me mind.

I wondered how long I have been working on this: looks like first metal was cut in June 2019. Not bad.

Before going too far I thought it would be a good idea to see if the wing still fits. Since it is a nice pleasant day, it was a good moment for a selfie.

using this image to see if things are square.

There is some work left on the aileron, once that is done, I’ll do the root rib. Somewhere in between I also have to build the servo/linkage/bellcrank.

Sounds like another fun week coming up!

challenging to get the shape right
this is not the same type of plane, but of similar origin/construction

 Posted by at 11:07 am  Tagged with:

Ailerons again

 Acroduster  Comments Off on Ailerons again
Oct 182020
 

Some of the drawings are not to scale, which is no problem if you build the full size version. A few important ribs are drawn full size, and from there it is easy to find the missing dimensions. Because the dimensions on a piece of paper are very hard to determine accurately, I found I needed to start measuring from the full size ribs on paper. From there it is easier to scale everything back to 1/3 scale.

There is a drawing with dimension to create the curved trailing edge, but there was no reference to the distances to the spars. Anyway, doing the extra work was not difficult, just time consuming.

dimensions for full size
wing goes down
this also gives the max deflection of the aileron.

Still trying to work out the trailing edge. It’s a 1″ alu shaped piece. Since it is not available any more, people use a traditional wooden one. However, since the ribs are quite small at that point I’m still not sure how to attach it. One option is the method using gussets on top and bottom.

trailing edge with some carbon for support.

Build support for the trailing edge and aileron spar. This should keep things lined up. Next step, attaching the root ribs to the trailing edge and build the aileron ribs.

While I have the router setup for cutting wood, I’ll do the nose templates for the ASK21 wing.

lots of filling and sanding to get to this shape!

Lots of fiddly bits, progress seems slow, but it’s raining, so who cares. Getting the aileron spar dimension correct is what is holding me up.

I am going to cut some negative ribs to slide over the aileron ribs, so that the trailing edge ends up where I want it. Even with the jigs on the building board I am not getting the right alignment results. Which probably means there is an error somewhere.

Sometimes you miss the obvious: there are no capstrips on the aileron ribs! that makes things easier. Tomorrow is another day, another challenge.

oh dear, is that not dangerous?
nah, get’s the job done. (4x4mm with 2 mm slot)
and some fun with the wingtips

one day I’ll turn this into a readable story, now it’s my diary!

That’s it for this week!

Ailerons bits

 Acroduster  Comments Off on Ailerons bits
Oct 102020
 
wing side part of aileron hinges

The ailerons contain quite a lot of parts. Apart from hinges, there is also a link to drive the top wing aileron. And the link to the bell-crank that is connected to the control stick.

now add some brass bearing bushings
a bit of riveting and we’re done

I started using a 1.5mm bit for cutting, it allows a higher spindle rpm, and better cutting of holes. Using the 2 mm bit to drill the holes was not really a good idea. Milling cutters are not drills! Also had to reduce the cutting depth per pass to max 0.3mm. A cnc router designed for wood does not have the stiffness do do any more. (At least mine does not) So with these settings and mild steel, things go great. The material for these parts is stuff from the local DIY shop, supposedly 1 mm thick. It’s more like 0.9, but I’m not complaining.

Drawings show full size part.

Anyways, just for reference: The original material is listed in ‘Standard Aerospace Extruded Shapes’, these ones start life as ‘AND10136-2403’ (AND stands for Army-Navy-Drawings.) It’s an aluminium T-profile to you and me. Finding out how it is supposed to be made makes it easier to make something that ‘will be close enough’.

bearing holes are drilled 2 mm, might go to 2.5 in the final assembly.

The result after paying close attention to alignment and clamping. This will do. Make a few more and on to the next step!

The reason I have 2 pcs joined is that I use 2 mm drill bits stuck through the outermost holes to align the blanks before bending. This ensures (hopefully) that that both end up equal.

 Posted by at 6:54 pm  Tagged with:

Cutting more metal

 Acroduster, CNC  Comments Off on Cutting more metal
Oct 082020
 

The truss tubes provide the for/aft strength of the wing. Since these are in place now, I continue with the ailerons horns and linkages. Once those are done, I can start on the aileron and trailing edge. Then only repeat 3 more times. Funny how some of the ribs look skewed, but it’s honestly the camera, real life is perfect. And that second nose rib from the left, even that is where it is supposed to be!

plans show full size, mine are mysize. 2024-T3 is what we used to call dural.
using cheap dowel for now.
0.85 euro dowels or 8 euro tubes.. I’ll think about it.

Making the aileron attachment points is next. Real life and drawing do not always match, but it’s close. (The base of the horn is approx 1 mm too high. Of course I should have measured that beforehand.) There will be a brass bushing in the big hole, and I will have a look if I can find 2 mm rivets. If not, the 2 mm bolts will do. Might put a bit of solder on the back, so that even when the rivets do nothing, it will still be stronger than needed. And I need to work out a clamp to allow accurate bending of that flange.

Aileron hinge: first trial part, forgot one ‘cut on the outside of the contour’ section. For the rest acceptable.

 Posted by at 7:05 pm

ASK21, lets start

 ASK21  Comments Off on ASK21, lets start
Oct 072020
 

I’ve been looking at it for too long, so let’s get going. As always, first things first. The wings are what keeps us up there, the rest is only there to keep the pilot dry and comfy.

taking the glider by the tail…

The kit I have was produced by Heinz Maassen Flugzeugbau. (I believe Heinz passed away early 2015) ….Die Maassen ASK 21 resp. später Mario Hermani (MH)-Flugmodellbau wird jetzt durch Jetisfaction produziert und vertrieben I read somewhere. However Jetisfaction is gone too. What stays are the gliders.

Long ago, Onki wrote a story, Another one here , More words.

Wings are of a typical foam/abachi construction with ample glass and carbon under the skin (I hope).

As copied from the wing root.

However, I think the trailing edge of the wings can be improved upon. So we starts the process by figuring out the wing profile. I don’t have a 100% guarantee I am right, but it looks like I have of Helmut Quabeck profiles.

To check I enlisted the usual suspect: Profili to import the profile coordinates (found at the top of the page on Helmut’s website), do the usual fake wing construction in Profili, print the ribs on a piece of paper and see how close we are. Main profile is close. And as already determined, the trailing edge needs work. Normally I would cut a plywood template, but I don’t want to mess up the router at present, I am still producing metal chips)

The red pen mark is what I have now.

Sanding the top of the wing down to the glass skin is easy enough, the bottom part is where it gets interesting. You need to keep the hollow bit accurate. Maybe I could make a printed sanding block? I do have the coordinates after all.

works! just had to add a steel wire, because the glass eats the plastic real fast.

With the knowledge of the profile, I can also print nose templates, the nose part is round-ish, but not the way a profile should be, that much I can say.

In the meantime I am trying to learn another CAD program, one that is a bit more up to date AND can talk to my router. Getting more difficult as the years go by. (not so much the learning, but trying to make old hardware work with new software)

This part was supposed to be a quick ‘slap on some glass and it will be ready’. You know by now, if I spot a challenge, I will go for it!

nose templates.

I think that I will sleep better if I change the leading edge. Will check the other wing tomorrow and decide then.

 Posted by at 6:07 pm

Making metal chips.

 Acroduster, CNC  Comments Off on Making metal chips.
Oct 012020
 

Finally getting the hang of producing chips in a consistent way. I think I need approx 36 pcs of the brackets you see in the second image. By the time I have those made, I’ll be an experd.

These by the way are fittings for truss-tubes in the wings. Once the wings are covered nobody will ever see them again.

Below is an image from the build process of a full-size version. The red tubes are 1″ diameter, the bolts at the bottom of the image are 1/4″ (6 mm)

All that stuff is not that big!

Brackets can be seen where red tubes connect.

My version of the brackets.

This post is following on from here.

Just another relaxing day

 Arduino, Jeti  Comments Off on Just another relaxing day
Sep 292020
 

I finally reached D-Day (Departure-Day) and have been taking it easy the last few weeks. Easy as in not spending time on modelling activities, but more time on ‘Life’ things. But, since a few days, Autumn seems to have arrived, so a good time to warm-up the soldering iron to keep the man-cave warm.

One of the things I needed to sort out was a flow meter for a Glider-Tug. Since a Flow-meter is just a lonely thing on it’s own, I decided to add a RPM sensor, and for good measure, a GPS. That makes it now a pretty good unit for Tow-planes.

Anyways, before you ask, I did not write the code to make it all work, just the usual tweaks to make it do what I want. Thanks goes to Thomas Lehmann for his excellent code.

only requires minor assembly..

Which leaves me to glue a few parts together. One of the lessons learned is that you really need to have a decent stable 5 Volt supply on your Arduino. Which means you need to feed it from a regulator thingy. I did use step-down regulators in the past, but especially around 5V input things did not always work as designed. Anyway, long story, I found some Buck-Boost regulators, that allow a wider range of input voltage, while keeping the output where it has to be. (and yes, this one is slightly different form the advertised one. Did I say no 2 parts are the same? Anyway, it does the same trick, so all is good.)

The regulator is rated for 600 mA, the total current for the unit is about 25mA, so well within specs. Input is max 12V.

One other Thing to keep in mind: most Arduino Pro Mini’s now are advertised as a ‘5V’ part. All it means is that the input voltage (VRaw) is supposed to be 5V. The onboard regulator drops that down to 3.3V (Vcc) . And when you then connect all your 5V sensors to the usual places, you can have a fair idea why things don’t work.

..fiddly stuff those smd resistors.

The Atmel328 on this board has 5V tolerant inputs, so it is safe to connect the RPM sensor directly to the input pins, same goes for the Flow meter. The flow meter also needs a minimum of 5V to operate.

Just for fun I’m printing a new box, life would be boring if I used what I had already.

GPS at the Top/Bottom, there’s even an arrow on the box to show which way the sky is.
..keep tuning the printer settings, think I’m slightly low on volume on the surface.

The only niggle I have at present is that the good people who sent me the flow-sensor, advertised it to include a connector. Someone must have borrowed it, because there ain’t none. I found an old 2S Lipo in my box of tricks and ‘borrowed’ it’s connector. Problem solved.

Next step, make some new PCB’s to replace the ones I got from Thomas. Those were designed for a slightly different Arduino. As with all these things, no 2 orders will give you the same parts. This is a general purpose board to which you can connect all the possible sensors that the software supports. Handy if you want to build 100 pcs, I don’t want to make that many! Given that the above assembly is so little work, the effort to make a new PCB is more for learning a new trick than anything else. As many times before, the software I used to work with is no longer available, it is replaced by something better.

All that’s left is to make the sensor cables, that should not take long.

Looking back a few posts make me think maybe I should add the airspeed sensor too. I did have some flights with it, but I need to get a much smoother display then I have at present. The sensor produces an analogue voltage, which fluctuates way too much. Filtering is needed, how much is a matter of mostly trial and repeat.

I’ll save that for the next one!

And see if I can make a totally optically isolated version. That would be handy too.

Next one after the next one. Maybe.

Do remember to change the MS5611.cpp in the linked library to fix the problem with MS5607 sensors! (for now, if I don’t get any more of these funny ones, I’ll let it be.) Or try to modify the main code to pick the modified library.

So for the next one I will remember which connector goes to what sensor!
One in the making, one ready to fly

So, enough on this subject, time for something else!

The first cut is the hardest

 CNC  Comments Off on The first cut is the hardest
Jul 252020
 

What took you so long? No idea.. More then 10 years ago I got myself a CNC-router with the idea that I would be able to metal metal parts. I’ve used it up to now mostly for non-metal parts. But retirement has given me enough time to finally sort things out. That and a better understanding of materials, cutting speeds etc. And after the smokies I had here, this is much better!

So, here we are: first part. This is a bit of steel which should probably not have that name. It cuts like butter, which is good for my confidence!

first part that was not produced with smoke and fire!
need to make a better jig, but the idea works.
and the final part.

The observing reader will notice that my hole sizes are off. Original is 6 mm bolts, scaled would be 2 mm. I feel that’s a bit thin. I’ll use standard 3mm ones , marked 8.8= 800 Newton/mm2.

  • M2, core area is 1.8 mm2. 1.8 * 80 =144 Kgf.
  • M2.5, core area is 3 mm2. 3.0 * 80 = 240 Kgf
  • M3, core area 4.5 mm2. 4.5 * 80 = 360 Kgf.

(not sure I have the right table here, check later! Values feel about right though) See here and this one

Ok, I’ll drill them 2.0 for now, looks like that is really enough. I’ll leave the one going through the spar at 3 mm, makes life easier. Yeah, I know, you should sort this out BEFORE cutting metal. Me thinks I’m due for a coffee break!

Trying with 0.6 mm stainless steel. It’s shiny, no other identification. Problem 1: it does not stay down on the board very well, so I really need a DOWN cut bit. (learned that in a hurry!) Not to be stopped that easy, I went slow, lots of cooling fluid, and managed these 2 parts. Progress is being made by counting the bits that did not work. Also, because the sheet is not fixed properly, I get some chatter, visible on the edges and general outline. All to be expected and just needs time to fix. I think it would also be better to have the cooling nozzle fixed to the head, moving around by hand as we go is possible, but not great.

clamp between 2 bars..
it works!

what a mess…..