Wednesday, September 18, 2013

New Project!

I have a new project that I am very excited about.  I have started scratch building a semi-scale Yak 52.  Now you may be asking, "Why scratch building?", "What is this semi-scale thing?", and "Why the heck a Yak 52?".  Well, let me start off with the easy one. What is semi-scale?  I've come to find out that in modeling this generally refers to something that is built like something but not exactly, and usually built larger or smaller than the original.  So, for my project, I started with drawings and pictures that I got from the Internet.  These drawings and pictures, though reasonably accurate, are not to scale.  In my project I have taken one of the drawings and "scaled" it up to the size I want to build.  So, although I have accurately scaled it up from a drawing, the drawing was not accurately scaled to begin with.  Clear as mud?

Flite Test swappable Nut Ball airplanes my daughter and I built
Why scratch built?  Well, I have enjoyed modding my existing planes and building some simple scratch built foamies like the ones at Flite Test (Check them out they do some really cool stuff with DollarTree foam board).
Then I hooked up with Daniel Madrigal on YouTube.  Check out his site!  This guy builds some really cool foamie jets completely from scratch.  Now I have the bug and I want to move on to my own scratch built planes.

On to the big question that everyone has, why the heck a Yak 52?  Yes, we can all see building a Yak 54, these planes are all over the place as one of the best aerobatic planes, but a Yak 52?  Well, it really comes down to the first time I was really exposed to this plane, and that was in one of my, and my oldest daughter's, favorite movies: Resident Evil: Afterlife.  In the beginning of this movie Alice (Milla Jovavich) along with Claire (Ali Larter), flies a Yak 52 from Alaska to Los Angeles and crash lands it on top of a sky scrapper.  First you may ask, "How did I even notice the plane with Milla Jovavich and Ali Larter?  Well I did and I fell in love with Milla,.. I mean the Yak 52 and have liked this quirky plane ever since.  I most likely would not be scratch building this plane except that it's really hard to find a Yak 52 kit, especially for electric.  So, I'm building my own.

How am I starting?

Like Daniel suggests, I'm starting with a "three view".  This is like it sounds, a drawing with three views of the subject.  I found several just by searching the Internet for "Yak 52" and "drawing", "plans", "three view", etc.  After selecting the one I liked the most, I had to figure how big I wanted to make it and how I was going to scale it up.  I could have used Daniel's technique of finding all of the "joints" and scaling and transferring  all of these measurements to a larger sheet, but I have laser printers and computers at my disposal and decided to use them to scale the drawing.  I started by deciding that I would like to make mine 5 times larger than my drawing.  This would give me about a 33 inch wing span.  The drawing I had was already sized for an 8.5 x 11 sheet of paper so once I opened it in my drawing program, I selected a custom paper size of 5 times 8.5 x 11 ( or at least 42.5 x 55 inches in my case).  Then I expanded my drawing dimensions by a factor of 5 in height and width.  From here I saved the new drawing as a PDF file.  From my PDF document viewer I had the option to print on multiple sheets of letter paper or, "Poster" print.  This then gave me a bunch of sheets that I cut out and taped together.

My enlarged drawing "Poster" printed and all taped together

Now, on to the build!

I started the same way that Daniel did with his planes that used bulkhead sections.  I started with a fuselage base to attach sections to.  I also started by normalizing and straightening some of the dimensions.  By this I mean that I took out some of the subtle curves and contours and also adjusted some of the dimensions to even increments.  The width of the fuselage base in the photo was set to an even 3 inches instead of the measured 3 and 1/16 inches.  I also had to estimate where the firewall would go and what I would make it from and how thick that would be (I decided on 1/8 inch plywood).

Then I started drawing out bulkhead pieces and shaping them down to compensate for the 3/16 inch foam skin I'm going to wrap it in.  I had some nice sectional views to work with that you can see in the previous photo.  These helped greatly in getting the shape right.  If I did not have these I would have been tempted to just make it completely round the whole length like I have seen other do.

 Here I have all of my sections cut out and trimmed for the skin and the center section removed (the lines through the middle in the above photo) to compensate for the fuselage base thickness.  You can see too the bottle of Fabric-Tac glue that I will be using.  I was going to use hot glue for ease and speed, but this was suggested by Daniel Madrigal and others as being lighter and stronger.  The tackiness does help with assembly but it does take overnight to really set up good.

Here we are with all of the bulkhead pieces glued in place ready to start putting in stringers from the nose to the tail.  I'll be using 1/8 x 3/16 basswood strips for this.  I was going to use balsa wood, but the selection I had seemed too soft and flimsy.  I opted for heavier but more strength.

That's all for now.  I'll have more soon.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Friday, July 12, 2013

T28 update and putting test equipment to good use

I really wanted to put my test equipment to use and I needed to check out my Airfield T28 with possible BEC/receiver/servo issues.  So I put it all together in this one big post.

This was a complicated subject with all the test equipment and airplane gear so I decided to try my hand at a video post.  So, here goes.

Thank you for watching my video post, let me know how you like this format.

Update to the video:

Further inspection showed that the faulty servo was not the steering servo but the door servo.  In the following photo you can see the bottom servo is the same servo that was over heating in the video.  You can also see that the push rod from the servo is flexed a lot.  This is obviously putting a lot of stress on the servo and is most likely the cause of the current draw.  Something will have to be done about this during the repair.

Stressed servo that failed

I have noticed that the current generation of the Airfield/FMS 1400mm Trojan T28 do not use a servo for these doors but instead uses spring linkage.  I may go this route for this repair and cut one servo from my count.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Saturday, July 6, 2013

Testing to the rescue

Some times stuff happens and you don't really know why.  This is why you need test equipment.

This was the case with my Dad's new 3D plane.  This was a kit that came without any electronics but had recommendations.  Since it was from Hobby King, of course the recommendations were for their parts.  No big deal, I actually like most of their parts.  I helped my Dad figure out what he needed and what was the best fit of parts from the US warehouse.  When he got everything together he noticed that things were getting hot.  Not a good sign.

He had a good idea of how to put a heat sink on his speed controller, since this is what was getting hot, and I helped him figure out the best way to put it on.  What he did was to use some heat sink compound in the center and then some epoxy on the corners to secure it down.  This was of course after cutting away some of the heat shrink to expose the ESC aluminum heat sink.  This is what he ended up with.

Darn good job, don't you think?

This is the other side showing that it is a Hobby King brand 25A (30A burst) variety.  This should already be a pretty good ESC and with the added heat sink, even better.  The velcro in the photo was something he added to help keep the ESC tacked down in his plane (nice idea).

After some testing, it was still getting really hot, too hot to touch and would actually go into shutdown mode!  This already happened once while he was test flying it.  We initially thought he had lost control when it went behind an obstruction, but we no longer think this was the case.

So, now to the testing and test equipment.  I was able to come down with the family and my gear (yes, family comes first. Since there was still some space left in the trunk I could take my gear along!).  We hooked up my power meter in between the battery and the ESC and began testing it out.

We found that at full throttle it was only pulling 14A.  This is well below the rating of 25A, but it was roasting hot after only about 30 seconds.  It even when into shutdown mode about 20 seconds later.  Even with the added heat sink, it was too hot to touch!

We then tested the power draw on my Wild Hawk which I upgraded to a brushless motor with a Turnigy 25A ESC.  This combination drew slightly more current at about 16A, but stayed quite cool and was barely warm after a minute or so of wide open throttle. 

So, this resolved why he lost control.  This also suggests that two other possibilities.  One is that the Hobby King brand parts (or ESC in this case) are not very good, or the other possibility is that they had a batch of much lower rated ESCs go out with the wrong labels on.  We would not have known this without the tester as we would not have been able see that the current draw was well below the rating.

Well, what does he do now?  He has two options.  One is to pursue a replacement from Hobby King and the other is to just go out and buy a more reliable brand.  Since the Hobby King ESC was only about $7, I think he will just look for a better replacement.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.

Saturday, June 29, 2013

Can't get enough test equipment

After a long hiatus, I am finally submitting a new post.

Since my last post I have learned a lot about RC equipment and testing.  This has led me to realize that I need another servo tester, or power analyzer.  This one does not control the server under test, but reports on the servo voltage and current use.  This is very important in making sure that servos are up to the task at hand and that the battery or BEC circuit is capable as well.

You may have seen one of my previous posts about my big T28 Trojan and my crash.  I suspected that this crash was due to power issues but have had no way to test this.  With this servo power analyzer I will be able to find out what is going on with the servo/receiver power system.

What is needed for this tester is a way to measure amps and voltage used by a servo, and all the way up to all servos including the receiver.

These are the parts that will be used build my servo power analyzer.

The parts consist of an amp meter, volt meter, project box, small circuit board, connector pins, and some connector lugs.  Also needed but not shown is some wire to make all of the connections.

This is a closer view of the Amp and Volt meters I used.  The Amp meter is rated at 5A max and the Volt meter has a rating of 10 volts.  Most of these testers that I have seen are setup for 500mA and 6 volts.  I chose these values so that I could monitor a larger range of current and voltage.

Another view of the inexpensive (about $6 each including shipping!) meters I bought on eBay.  These are inexpensive, but they'll do just fine.

This is a better view of how the circuit board and pins will be used.  The pins can be snapped off in the number needed.  Since these will be used for servo connections, these will be broken off in 3s.  The circuit board will be cut in half and one half used for each end.

This is how the completed tester looks with the two meters mounted on the face.  The connectors are on each end.

These are the pins for the output or servo side.  I opted to provide two connectors here so I could hook up two servos at a time.  I could also use a splitter cable as well but this was easy enough to add.

This is the input side (sorry for the blurry photo).  There is no need for more than one input here.

This shows a typical setup for testing a servo.  With this setup I can monitor any voltage and current fluctuations while the servo is put through its paces.

The way I plan on using this to test my T28 setup, is to plug the BEC into the input side and the receiver with all of the servo connections into the output side.  Then I will monitor for voltage fluctuations (anything dropping much below 6V) and maximum amp flow.  Anything above the amp rating of the BEC will be a sign that it is not up to the task or I have a problem with a servo or two.

I realize that I did not include a circuit diagram and this would be very helpful for anyone wanting to make one of these.  It's really very basic and should be easy to duplicate.  So, here it is:

The positive voltage path flows through the Amp meter.  The voltage is measured the positive and negative voltage paths.  The servo signal wire passes straight through without interruption.

Thanks for stopping by my blog.  Please feel free to post comments, good or bad, and be sure to come back and check for future posts.