March 2008 Archives

Repairing the Citabria

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Purchased the gear box and prop today.

first_solder.JPGCarefully soldered the new motor in, taking care to match white to white and black (new) to red (old) motor to ensure correct polarity. Covered the joints with some ultra thin heat-shrink tubing I thought I'd never use.

ready_to_glue.JPGReady to have the prop attached. Notice (barely) the threaded shaft. It is right hand thread - I at first thought it might be left-handed, but I think I over analyzed that too much.

prop_attached.JPGAttached the prop.

When I tested the motor, to my horror it spun BACKWORDS!

Let that be a lesson to everyone - don't assume the wiring on these motors is correct, test the connection before making it permanent. I had to carefully cut the heat-shrink off, unsolder the wires and re-solder them back together.

correct_polarity.JPGThis time it spins the correct way.

glued.JPGA bit of white glue to hold the motor back in the mounting holes and we're ready to fly again.

taped_ready_to_fly.JPGWill see how it goes on Monday.

AMP D-SUB Crimping tool for sale

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amp_58074_tool_9pin.JPGI was going through my tools last night, and I came across this gem that some of the more serious builders might appreciate for wiring up a bunch of serial or parallel connectors. I even have a 25 pin male and female connetor to through in (I also had a male 9pin, but I crimped a wire in it to test the tool - works beautifully). Other then trying it out, I have never used it, and after seeing what they sell for new, I figure the few times I need to make a d-sub connector I'll just solder the wires manually. I could use the cash to buy plane parts.

Both Digikey and Jameco still stock these, so I'm thinking there are people out there who would appreciate one for less then full blown retail.

Total price from Digi-Key $266 plus taxes & shipping (Jameco was over $400! Yikes, who shops there???).

In the end, this tool is a time / money trade off. Those with money and little time will appreciate it, those like me with little money and (hopefully) more time can't justify the cost - hence the reason I'm looking to sell it.

As for the cost of the connectors, based on this page from Digi-Key,

The 9 pins seem comparable (male connectors are the same price), however, they do get quite expensive compared to the soldered connectors as the number of pins rise.

Any takers for $100 US plus shipping? Theres a good chance it will be put up for sale on eBay over the next few days.

Powerful Lady - still not able to beat a tree....

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Ok. I've been busy as beaver in the shop. I want to fly the sailplane, but for longer then a few seconds and with the ability to abort a landing should I be messing up. So, I have borrowed the motor, prop and speed controller from a Microwhiz plane I purchased last fall (it is way to acrobatic for my skill at the moment) and built an engine mount for the Sophisticated Lady. I bought a piece of 6 x 9" airplane birch plywood 1/16" thick and proceeded to replace the canopy with a frame to hold the engine.


The darker wood is a piece of Oak - not the sort of wood normally found in light airplanes, but it is strong, and available - which made it an excellent choice for me. Notice the wood dowel coming through the front, the fit is nice and snug. Along with the rubber band strapping the back down, the mount does not move. The plywood is quite flexible, so I added a 5/8" wide strip of plywood running crosswise to reinforce the bolts.


A close up of the engine mount. The prop has room to swing quite comfortably in front of the nose of the glider. (About 3/16" - Lots! :-)


Balancing is always important. The main thing is to ensure the center of gravity (C.G.) is as close to but NOT BEHIND the point mentioned on the plans. Typically this means adding weight to the nose to bring the CG forward. The Lady had about 2oz of lead and steal in the nose to keep it down. That was all removed. When the larger of my 2 batteries (3 cell 1500mAh Li-Po) is installed, the CG is just slightly ahead of the ideal spot. This will make the plane fly faster, but handle better (a good thing for a rookie like me).


And finally, all painted up and ready to go!


So, the next step is to fly it right? Well I did just that today. There was a gentle breeze from the South, so I loaded up and went out to the local school grounds to try it out. Rev'd up the motor and with a gentle toss into the wind away it went! Beautifully! It works quite well. Climbed to about 100' feet and eased back for some level flying. The landing wasn't graceful, but no damage. In fact, I actually tried to abort the landing and so tagged the ground with the motor running at about 1/2 throttle. No damage to the prop or mount.

The next flight started just as well. I was coming around to try and land but realized I was too high and too far back, so gave it full throttle to climb out, and flew right into a tree. Sigh. The prop and tail broke - but not the engine mount!

The damage wasn't too bad. The tail was glued back together in about 15 minutes once I got home. And I even managed to glue the prop back together, although I suspect its days are numbered.

Binary Clock project - Using an obscure MC838

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I'm trying to build a binary clock with some surplus digital logic chips I have laying around. The chip of choice it seems would be the 7490, of which I have 1 that works properly and 1 that seems to only work if I leave it in the default mode of counting from 0 to 9. I also have a number of chips stamped with MCC838, which turns out to be a decade counter like the 7490.

The main exception is the 838 has 4 inputs to explicitly set the bits with and a single reset line. I need to configure 3 counters to reset after reaching 5 (on 6 reset to 0). With the 7490, just tie the second bit to one reset and the third bit to the other reset and assuming the chip works, it counts 0, 1, 2, 3, 4, 5, 0, ....

Studying the spec sheet I could find on the MC838 leads me to believe that by using a NAND gate on bits 2 & 3 the result should nicely drive the CD (reset) line from High-to-Low and hence reset the counter back to 0. However, that is not what is happening. Hear is the observed output:

1 2 4 8 NAND

0 0 0 0 1

1 0 0 0 1

0 1 0 0 1

1 1 0 0 1

0 0 1 0 1

1 0 1 0 1 - at this point, the next clock should create 0110 (6) and the NAND goes low (0) which should reset the 838 counter and start over. However, the counter just skips 6 & 7 and carries on with 8 as follows...

0 0 0 1 1

1 0 0 1 1

0 0 0 0 1

Any ideas?

Slowing down to speed up

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I'm stealing the phrase from a project manager - it sounds too cliche to be his original so, to whoever coined the phrase, thank you.

That said, after spending a couple Monday's in a local school gymnasium watching a variety of pilots flying various smaller electric planes and helicopters and even test driving a plane thanks to a generous member of the group, I have decided to actually invest in a small indoor RC plane to build some basic flying skills.

citabria_stand.jpgcitabria_box.jpgThe plane in question is a Parkzone Citabria. A very light (20 grams), 3 channel airplane. The plane comes complete with a 2.4Ghz transmitter and receiver, so there is no channel conflicts, just power it up and fly!

Tonight will be my first go at really learning to fly. The battery lasts at least 10 minutes per charge, and takes about 15 minutes to recharge, so I should get over 1/2 hour of good flight training / practise (compared to the 30 seconds or so per flight I have had to date). I am looking forward to it.

Over the weekend I put up a couple pages documenting my RC experience to date. The main reason for needing to get better at flying is evident by my attempts at flying a sailplane. I was given a Sophisticated Lady RC sailplane last fall and after getting it flight ready, proceeded to get more experience repairing it then flying it....

... later that evening....

Well, I just got back from almost 2 hours of flying and watching. Between charges I managed probably 30+ minutes of actual flying and was getting quit good at it. There was an initial scare as I tangled with a much larger bird - the sound of a prop tearing through styrofoam isbelly_wound.jpg unmistakable. The collision was mid-gym 15+' in the air and I thought I was done. However, I pulled out of the dive and managed to keep flying. After a couple more laps with no sign of problems or missing bits I brought it in for an inspection and notice a nasty but fortunately not fatal gash on the belly. I'm not sure when the chipped prop happened. That it is also lying on the belly is the next story.

broken_prop.jpgAgain, the big crash is always on the last flight - if I had packed it in a bit sooner, all would have been well. Wind up to a few weeks ago when I was test driving a Cessna, and flying full speed, full throtle straight into the wall. At least 2 or 3 times I crashed hard enough to tear the engine mount off the frame and it had to be reglued. Turns out the weak motor mount may have been saving it from a bigger disaster. Tonight I again got a bit close to the wall, however, this time it was not straight on, gearbox.jpgbut a glancing blow that caught the wing and torqued the plane into the wall. As it fell to the ground, I noticed the prop fell seperately. Alas, I actually managed to break the shaft. So RC-EHUD the Parkzone Citabria is grounded until I can purchase a new motor / gearbox / prop assembly. Apparently they are only $13.99, so I should be back in the air soon enough.

Total airtime on this frame is 30 minutes for sure - quite possibly more, I wasn't really counting. I went through 3 batteries and ran each battery for about 2x5+ minute flights.

Happy Pi Day!

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Today is none other then Albert Einstein's birthday (happy 129th birthday!), noted as 3/14 (or 3.14) and hence Pi Day. So, make sure tonight for dessert you have a big piece of pi[e]!

ATI Radeon 9600 for sale - sold!

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ati_9600.jpgI am currently selling an AIT Radeon 9600 All-in-Wonder video card complete with drivers, remote and cables. This is the one with the built in TV tuner and video capture hardware. I never did end up using the TV tuner part and when my computer received an unscheduled upgrade last month to PCI-X, the AGP card quickly had no useful value to me any more. The card is (was) for sale on eBay. Thanks to all who bid!

Start of a new day^h^h^hsite

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Well, here's something I've wanted to do for quite some time. Start using a real blogging tool. So this short and sweet post is just to get things started. I will leave all the pages, pics, etc. where they are for those deep linking in from other sites.

The original start page is still available - I'll leave it around for a while (I rarely delete anything).

For those that might have missed it, I'm asking for help in identifying an old airspeed indicator I purchased off eBay a few years ago. Here's some photos:


airspeed1.jpg  airspeed2.jpgairspeed3.jpg




UPDATE - March 7, 2008

Thanks to Ed (a member of the group), I have some more information regarding this instrument. A site call has a Lancaster ASI about 3/4 down the page dated 1943 that looks identical to mine (except theirs doesn't have a broken mount).

SpitfireSpares has theirs listed at 115 British pounds, or about $225CDN. I think I'll put mine in a safe place for now.