12V, High Current ATX Power Supply Mod, Part 1

My hobby charger, like many of them, runs on 10-18V DC, which is rather handy, as it allows you to use crocodile clips to connect it to your 12V car battery when you’re out flying somewhere, which is the handiest power source around. But, when it comes to home charging, this means you need a high current DC power supply. These can be rather pricey…or are they?
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Hmm, what’s this? I like hackable parts.

Enter the PC power supply unit, or PSU for short. These can readily be found anywhere for free, just watch for someone throwing out a desktop computer. Being a geek, I tend to get a few old computers, and when I saw this 450W power supply I knew I’d have a use for it someday. Well, I had done this once before, for my dad and me when I was younger, and I knew it wasn’t a hard job. The label from the above picture says I can get 12V at 18A, which is pretty dang good. That’s 216W, and I only have a 200W charger at this time, so I should be able to use the charger to its maximum capacity, something I’ve only been able to do with a car battery as a power source until now.

I have to go, so I’ll just leave you a picture, but I have the power supply in working condition. I get somewhere in the neighborhood of 12V, which is cool with me, but I didn’t do extensive testing yet as that’s not a smart thing to do with the current state of the power supply. Nothing is protected against shorts right now, so even just checking the voltage had a potential hazard. Not to me so much, but mainly to the power supply, as one slip could short the output and render the power supply useless.
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It’s not nearly as dangerous as it looks, just don’t touch the fat traces on the printed circuit board…

Still to go is a power switch, two power status indicator LEDs, and lots of liquid electrical tape slathered on all the cut wires and soldering joints. This, as well as the process used to convert an ATX power supply to something useful outside a computer, will be covered in part two.

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Construction Has Begun

Finals finished yesterday, for me, so I now have about a month with a lot more free time on my hands then I’m used to having. This is a good thing, I needed a break. It also means that I can, and did, start construction on my quad, for which I received all the parts to build back in October.

Right now, I have assembled the frame, which was made out of a 6″x6″ piece of 1/4″ thick birch plywood. This is the “body” of the quad, the platform upon which everything will sit. On the bottom, I attached the four arms with wood glue. The arms are 1/2″ square basswood, each 13.5″ long.

Here, I am aligning the arms onto my workbench, and using tape to secure them so they don’t move until I can get them glued. Not shown, but I also taped the arms to each other in the center, for gluing.
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I applied glue to the arms.
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I applied pressure, and wiggled it back and forth slightly until it felt “attached”, then held pressure and used my PowerShot staple gun to sink in two brads per arm, to hold them in place while the glue dries. The strength comes from the glue, not the nails. The brads were flush sunk with a hammer, as the staple gun leaves them sticking up about a millimeter or two.
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Yes, that board is 6″x6″, and yes, I have big hands.
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That entire process went really quick. I didn’t show it, but the plywood came as a 12″x6″ sheet, and I simply used a miter saw to cut it in half for my quad. Nothing fancy there. Here is the quad as the glue dries.
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Lots of cool stuff in this picture.

I have to go run some errands, but once I come back, I plan on starting some work on the quad’s electronics, so there may be another update today still. If not today, tomorrow for sure.

On Writing Blogs

Writing a blog is work, plain and simple. It might not be for others, but it is for me. Someone may ask why, and that’s understandable, after all, all a blog owner has to do is put some words down on the screen on a semi-regular or regular basis, right? Well, sort of, but not quite. First off, you have to have something to write about. Secondly, you need to have the time to write something. Thirdly, you have to have the desire to spend a fairly sizable chunk of time writing your blog post. Finally, all three of the above things have to happen at the same time. You might not have something to write about, even if you have the time and desire, but more often then not for a type of blog that I have, talking about projects, I’m much more likely to have something to talk about then the time or desire to actually talk about it on my blog. Indeed, a lack of desire is why I haven’t posted since the middle of October.

My lack of desire stemmed from being fairly busy, after all, I work 40+ hours a week at night, go to school in the morning, and sleep in the afternoon. Even such, I still have plenty of time I waste mindlessly browsing the internet, where I could have instead brought up WordPress and started a draft, which I could write in increments, right? Well, right. But I didn’t, because when I didn’t need to work, sleep, do homework, or be in class, I would rather see my girlfriend, catch up on my motorcycle forum, or check up on the latest position of the New Horizons then to sit down and spend an hour wrestling with my jumbled thoughts until I spew something somewhat legible onto the page and hope someone finds it interesting or useful.

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An artist’s rendition of New Horizons as it will appear during its flyby of Pluto and Pluto’s moons on July 14th, 2015.

The bottom line is, however, that the more free time I have, the more likely that my desire to update my blog happens at the same time as I have time to write the said update. And, lately, I just didn’t have much time. Today, I just took my last physics test of the year, yesterday, my last calculus test. I have no homework due for tomorrow, which is unusual, but a result of classes winding up. I have three more lecture hours left, in three different classes, two of which will only be review for the final, the third (statics) I’m not quite sure (but homework is due on Friday for statics). I have one final Monday, and two on Wednesday, and then I’m done for the semester, which I’m pretty excited for. You might think I should be studying for my finals, but one can only due so much, before a point is reach past which extra studying in no good, and that point was reached today. Not only did I get unusually short on sleep this week, but I had review for the final in calculus class this morning, followed by doing homework for statics, then statics class, then last minute review for my physics test and filling out my note sheet, then my physics test. After that, I was pretty sure extra studying wasn’t going to do me any good, so after talking to a couple of people at school, I came home and just chilled. During this time, I decided to update my blog.

This post itself is another reason I avoid writing these when I only have an hour or two of free time, and that’s because this post itself is quickly heading towards the one hour mark. I’m currently at about 50 minutes and just over 630 words in this post, as I write. When I start writing, I generally don’t write just a sentence or two, and I generally like to finish it instead of saving it, which is why this post will end up taking over an hour to write, all in one block. If I wasn’t writing this, though, I could have been causing chaos in Just Cause 2. Do you know how much stuff you can blow up in an hour in Just Cause 2? Quite a bit, in case you didn’t know.

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Looks like someone’s having a bad day.

Not only do I tend to write a bit, and want to get it all done at one, but then you have the time it takes to find or take, edit, and upload images, get the link codes, then correct mistakes, edit, and preview the post, find another mistake, and so forth, until the publish button is hit, and the post is complete.

Before I leave, I would like to mention a couple of things, which will probably receive time in future blog posts. First, I bought myself a rubber ESD mat for electronics work, and I’ve built up a 0-30V, current limited power supply…well, the part on the protoboard, that is. Second, I’ve bought my first high power LED flashlight, 600 lumens. Yeah, that’s bright. Third, I have not forgotten my quad, by any means. I plan to start the construction next week, when finals are over. Expect more blog posts at that time, as well.

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I told you it was bright, but you didn’t believe me now, did you?

Finally, It Has Arrived

When I woke up yesterday afternoon, I was pleasantly surprised to see two boxes sitting on the table, as I had only been expecting one. Around the start of October, I placed a second order for my dad and myself, for a couple more props, a LiPo back, an ESC for the airplane I plan to build, some XT60 connectors and some balance charge extensions. This order arrived in New York by the forth, much faster then my initial order had taken, and within a day had been processed and shipped on, so I expected it soon. However, my quad order, which was placed a week and a half before then end of September, was still listed as being in New York. Indeed, when I checked the tracking yesterday after it had arrived it was listed as delivered, with no updates between New York and Illinois. Either the USPS has invented teleportation, or their tracking sucks, and I’ll place a large bet it’s not the former.

Although pleasantly surprised that my quad parts had arrived, there was a second reaction bearing a certain foreboding, as one of the boxes was pretty crushed in shipment.
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Somehow I just knew the crushed box was my quad parts, the box that was three times as valuable as the other one, and indeed I was right. My biggest concern was the LiPo battery, and that it might have incurred shipping damage. The USPS does not allow international shipment of any sort of lithium batteries, so if I needed to return the battery it would have to go back via EMS or UPS and would probably have cost more then the battery was worth. Luckily, it was the best packed item in the shipment. It was wrapped in foam film, for lack of a better term, the type of packaging material usually used to wrap TV’s and computer monitors. Then it was placed in a small box, wrapped tightly in bubble wrap and taped securely.
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Not only that, but checking the cell voltages showed that all cells were at 3.85V, exactly matched, and a little research also told me that 3.85V is the voltage you want your pack at for the longest storage life. I haven’t tested the pack yet but it’s off to a good start just from the voltage check.
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In what initially seemed the opposite, everything else seemed to just have been chucked into a giant bag and thrown into the box. Further inspection told me I need not have worried, as the motors were wrapped in more of the foam-film, and honestly, nothing else was very fragile anyway.
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All in all, the contents of my $180 worth of parts from the order I posted about when I started this blog seemed slightly underwhelming. I expected…well, something else, I guess. I suppose it has to do with the fact that I have a lot of time ahead of me in testing, balancing, and building before I get to play with it.
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The second order which I did not mention on the blog in detail yet contained two fire resistant fiberglass LiPo charge sacks for my dad, which are referred to from here on as Lipo sacks, and one for myself. It also contained balance lead extensions for 3s batteries, so that the batteries would be able to sit inside the lipo sacks while charging, as the attached lead is fairly short. It also contained 4 servos and one ESC for upcoming my upcoming planned airplane(s), XT60 battery connectors, and a few more spare props. Although one third of the cost of the other order, it took up about the same table space.
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At this point I unwrapped and opened everything but the small items, and arranged them next to each other. I will cover details on the individual parts as I come to them in future blog posts, must likely as I test or attach them to each other and to the quad.
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Still much to do (well, everything, really), and I still have to move. I probably won’t be able to resist playing with it somewhat tomorrow, but I will need to sleep for a good period of the day as I am currently very short on sleep, and after that I will most likely do a little more packing and cleaning for my upcoming move. I’ll update later when I have something to update with.

We Interupt This Programming…

I must interrupt this non-regularly updated blog to move. My roommate decided to move out of the apartment, so I have decided to move too. Too expensive for me without a roommate. I found another place to live but even if the parts decide to ever finish the long trip from China and the postman rings my door, I’m going to be busy moving. I have until the end of October to move, and I have to do this around work and school so it’ll eat up most of my free time for some time.

However, on the other hand, once I’m finished moving I’ll have a roommate who is into RC cars (I also have one), has dabbled in airplanes (I’ve flown a few of those), is very interested in quads and does embedded programming, so I’ll have someone to work on it with.

Updates – 9/27/12

I now have the flight control board, the Naze32. It was surprisingly small, the picture on the website was bigger then this thing really is. For a size comparison, I set it on the keyboard of my laptop.
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That was nothing compared to the FrSky telemetry link that came with it.
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I have hooked the board up to my computer and with the MultiWii GUI interface I could see the sensor outputs changing as I moved the board around, so everything seems to be working.
I’m at school right now, but over the weekend I plan to do the following, including documentation here on my blog:

  • Pick up a cheap multimeter from Harbor Freight for testing components.
  • Finish my JR6201 72Mhz to 2.4GHz FrSky conversion.
  • Cut the sheet of plywood for my quad base, and glue on 1/2 inch square, 24″ long basswood arms (yes, another design change).
  • Update the firmware on the Naze32 and learn the interface so I know what to do when I have my quad built and I’m eager to fly.

I’ve got a whole lot of research left to do, mainly stuff that applies to FPV, when I’m ready to get that set up. But I’ll tackle that when it comes to that. I believe FPV will be really, really fun.

A Frame Design Change

The other day, I stopped at the hardware store to see if they had small pieces of wood, and their selection of aluminum caught my eye. I pulled out a hollow square tube and while it was extremely rigid, it was also too heavy. However, I’ve seen lots of stuff with holes drilled down the length to lighten it up, so at school on yesterday I stopped by to ask my Engineering Statics teacher how much holes reduced the strength of material and such. I never actually asked him, as I started telling him what I wanted it for, he asked some questions on weight and thrust, and then recommended I use some basswood about the dimensions of an average wood yardstick (1″ x 0.25″?), oriented vertically. Then, because it would want to vibrate left and right as it’s narrow, simply get some fishing line and run it from one arm to the next all the way around, making a square of the fishing line. A quick sketch is handy.
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I just used Paint, as I’m feeling too lazy to make a better one in Sketchup. The arms and plate will be made out of wood, no aluminum is planned now. The red line indicates the location of the fishing wire which stabilizes the arms from moving in the horizontal direction. Making it this way should make it pretty light.

My teacher also told me if I want it really light I use a simple truss instead of solid wood, and we start talking about simple truss’s in class tomorrow (now today, Friday). I said I would, but not until I know how to fly good, I don’t want to spend hours making a truss only to destroy within minutes it cause I crashed on my first flight.

My prop balancer arrived today. Looks pretty nice, although I haven’t used it yet. I’ll report back on how I like it once I have props to use it with.
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On Wednesday I ordered a 5kg digital kitchen scale, so that I can weight parts as I go along, measure motor thrust, and try different frames in the future to find the lightest ones that are still strong enough for use. Less weight equals less power needed for flight, and less power needed equals longer flight times. I also just recently found a post on RCG that said that for a given frame, the longest flight time will be with a battery that weights the same as the frame does. So lighter frame also equals smaller battery, which is cheaper, and cheaper is always good.

About three hours ago I got an email from HobbyKing, saying my package is packed and sent to shipping, and to allow 48 hours for tracking information to appear on the website. So as long as it doesn’t get stuck in customs, it shouldn’t be too much longer…