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.
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.
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.
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.
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.
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’.
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.
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!
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.
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.
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.
Wings are of a typical foam/abachi construction with ample glass and carbon under the skin (I hope).
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)
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.
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!
I think that I will sleep better if I change the leading edge. Will check the other wing tomorrow and decide then.
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.
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.)
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.
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.
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, enough on this subject, time for something else!
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!
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.
Finally got the airspeed sensors, so what better to do on a rainy afternoon them to play with them? First the specs: Datasheet, and a picture. Bear in mind that all these diy chips are basically old stuff. This one dates from 2012. Obviously nothing wrong with them, they are still used in a lot of equipment, but they are not the smallest of parts! However, this makes it so easy for us diy-ers to play with them.
The metal probe weighs approx 10 gram, with electronics, housing etc, ca 40 gram. (too much cabling, and unwanted plastic). I don’t want to stick that on the tail of a glider yet. I’ll use that on the wingtip of the Carden. ( I think, maybe, or something). Easiest for testing is to connect the sensor to the input of my JetiBox. (I think this can be done) and stick it on the car. We’ll see where this goes.
Some how the Jetibox only displays 14 sensors, (supposed to be 16) and most of them are for the GPS that is not present and disabled. I guess I have to ‘fix’ the software for this. Can’t think of another way at the moment.
The sensors-information must be stored along with the Rx identity in the JetiBox. (Not in the transmitter, in the JetiboxProfi box thingy.) Good project for another rainy-day, because I suggested to one of our BigGlider guys that I could use this to monitor ‘from the side’ if and when he has signal dropouts. I can do it at the moment, but I would still like to see the airspeed at the same time. That was the idea behind the stand-alone system. Stick it on anything, and monitor from Jetibox. Actually, with all the sensors on board you could monitor lots of things, without having to interfere with the electronics of the plane. (Fokker-E3 rings a bell, what speed is it really moving, and would it not be nice for it to complain when things are getting dicey. Just a thought…)
Wingtip? If I add a small 2s 150mAh lipo it will be a completely self contained, stand-alone unit, that is connected to the DS-14. Weight is easily added to the opposite tip to balance things. That, or stick it an the rudder, the Carden won’t mind so much. Much fun to be had!!
And in the meantime, our friends delivered a bunch of cutters for the CNC-machine and some parts for making a mist-cooling system. As always, the general idea is present, the execution is still to be puzzled out. Where do I put stuff?? On the router head so it moves along with stuff I cut, (wishful thinking) , or nail it to the bottom and for the few small parts I have to make it is ok to simply spray enough the centre of the part. And I need some cutting fluid. Look for local cutting fluid, and start doing it!
This series has an extra voltage regulator, I have a feeling the version that runs straight on the 5V from the receiver is a bit too sensitive to voltage fluctuations. These ones are to be fed from a 2S Lipo or LiFe supply.
Continuing with the Barometric Pressure Sensor saga. Here are the data sheets for the MS5611, and the MS5607.
The parts that show the different methods for calculating pressure and temperature are highlighted in the images.
Use the linked datasheets if you can’t read the fine print.
Crudely changing the code at least gives me good results now! Next is trying to merge this in the VarioGPS code. One way to do it is to use the chip-select bit to determine which chip.
I2C INTERFACE COMMANDS Each I2C communication message starts with the start condition and it is ended with the stop condition. The MS5607-02BA address is 111011Cx, where C is the complementary value of the pin CSB.
Pulling it high will give an address of 0x76, (normally pulled to zero by 2k2, gives it a 0x77 address.) VarioGPS already uses this trick to identify another chips. I might ‘simply’ put the MS5607 in that slot, since I don’t have that chip.
Memory is already tight, so I removed both the LPS and BMP280/BME280 sensors. That gives me enough room to play and get the code inserted and cleaned up. I can always stick it in later when/if things are working.
RAM: [===== ] 50.5% (used 1034 bytes from 2048 bytes)
Flash: [========= ] 91.6% (used 28144 bytes from 30720 bytes)