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Posted by devinvagt | Jul 19, 2017 @ 01:49 AM | 1,423 Views
I've been reading about the fancy carbon fiber filaments for 3d printing, and I just had to know if they were worth the money. So I bought a bunch of them, and made a 3 point bend test setup to see how they perform. I made a video, which you are of course invited to watch, and all the data is available on a google docs spreadsheet.

Vocab: specific ultimate strength is the force needed to break the material divided by its weight. Flexural modulus is how stiff a material is, independent of its geometry. Toughness is how much abuse the part can take before failing.

3d printing Fancy Filament Face-off! ( carbon filament bend test ) (7 min 31 sec)

In brief, the best all-around filament are the carbon filled nylons: the two I tested had similar performance so it's just personal preference. There is a graph below vs. regular PLA.

Runner up prize goes to the carbon filled PLA and HTPLA. I tested three types and they also performed similar to each other Not as strong or tough as the nylons, but significantly stiffer. Graph is below

Worst filament tested is the carbon filled ABS from Oo-kuma. it is not much better than regular PLA, and in many ways it is worse. Cannot recommend.

All the filaments tested are shown in the other three charts, sorted to show the winners and losers.

In general: adding carbon adds to a material's stiffness, takes away from its toughness, and leaves its strength unaffected.

I hope this helps you in your 3d printing endeavors!
Posted by devinvagt | Dec 05, 2016 @ 11:42 AM | 1,905 Views
The HMDVR either works perfectly, or not at all. When I put the micro SD card in my computer, I often find an empty directory, no files at all where videos are normally saved. During recording, the light blinks and all seems normal. I haven't been able to figure out what is wrong or how to fix it. My current theory is that the dvr is reading the micro SD as write-protected, but continuing to try to write to it anyway without throwing an error, or that the SD card is not rated for high enough data rate. I think I am done thinking about this dvr. I ordered a Eachine prodvr today; if I can throw another $20 at this problem and fix it, I can live with that.

EDIT: I think I found the problem, I was running it off a 7805 5v regulator, which needs at least 7 volts to run properly. I was running it on a 2s lipo, so yeah sometimes it was probably not getting enough power. I switched to a dc/dc converter that can handle down to 6v and so far so good!

EDIT: Finally gave out after working for a while. Not sure what happened but I think it's time has come. Can't recommend this dvr.
Posted by devinvagt | Jul 12, 2016 @ 11:55 PM | 2,558 Views
While working on our sub-250 gram fixed wing fpv racer, we got into a discussion of what combination of motor, prop, and battery would suit this plane the best. For a motor, we started with the Emax cf2805 1300kv and the Hurc 300 'blue wonder' ; two very similar motors. They're about 29 grams and can handle in the neighborhood of 10A continuous. A little overpowered for our purposes, probably, but a good place to start. Later, I added the power up 250 plus 1400 kv ( tested as 1290 kv), a slightly lighter motor with similar performance, but with a little lower amp capacity.

I wanted to gather some real-world numbers we could rely on, so I tested props with the type of batteries we would likely use in a small model, i.e. small 2 and 3 cell lipos in the 500-1000mah range, at ~80% capacity. I tested static thrust because it's the easiest to measure, and for maneuverability and hovering it's a good guide to what you can expect in flight.
What follows is the results of the testing, sorted by max thrust, thrust/watt ( what most people are interested in ), and thrust per gram. In general, the trend is simply: as thrust goes up, efficiency goes down. The trick is to find the right balance of power, weight, and efficiency. I also averaged out the score for thrust/gram, thrust/amp and thrust/watt and gave each combination a score. it's useful to get an idea which combinations are a good balance.

Some of the standouts that are worth checking out:
Best overall...Continue Reading
Posted by devinvagt | May 05, 2016 @ 01:29 AM | 6,357 Views
I have been testing a new lemonrx receiver+ stabilizer combo in my sub 250 gram plane and I've found it works well in close. BUT... I've been getting a loss of control out a farther, say, past 0.25 mile/ 0.4 km . In two cases, I still had pretty good servo control to land, but no motor response. So I did some range testing in my back yard and I was able to replicate this situation pretty reliably. It comes down to how the receiver failsafe handles signal loss.
When the lemonrx receiver loses the signal, it sets the throttle to zero. No surprise there. But when it reacquires the signal, it does not restore throttle to its previous value. Rather, you have to move the throttle stick up and down for a while, sometimes for as long as 10 seconds, before you are given back throttle control. During this time you have varying amounts of servo control, which is a big help when you're trying to pick a spot for an emergency landing. However, in the most recent case I was flying over a lake and had to land in the water, so there were no good spots to be had (I swam out and fetched the plane -- it's OK now. )
So what to do? A mini-shootout, of course. I ran a range test setup with the diversity lemon rx combo, a diversity lemon rx receiver, an orange rx r615x, an orange rx r620, an old spektrum ar600 with a couple of split-v dipole antennas( a la Ibcrazy) attached, and a brand new spektrum ar610. I should add that my transmitter for this test was a spektrum DX6i...Continue Reading
Posted by devinvagt | Apr 25, 2016 @ 12:36 AM | 3,862 Views
EDIT: added the 1200tvl

I've been trying out some different mini - cams for my sub 250 gram fpv race planes and quads. I've checked out seven cams so far, in ascending order of weight ( with cable attached, cam is no good without a cable! )

Diatone 4g
Tarot 7g
Eachine 10g
Aomway 600tvl 11g
Aomway 700tvl 11g
Aomway 1200tvl 25g

and price (as of mid-2016) :

Diatone 600TVL 120 Mini Camera Black $13
Eachine 700TVL 2.6mm Lens 1/3 CMOS 110 Degree $14
RMRC-Pico wide v2 520TVL $15
Aomway HD Mini 1/3'' CMOS 600TVL 2.8mm $15
Aomway 700TVL HD 1/3'' CMOS FPV Camera $30
Tarot 520TVL FPV 1/4 120 Degree Wide Angle Lens $31
Aomway 1200tvl 2.8mm lense $45

I strongly suggest going for the highest quality camera you can, it's your main source of information when flying and a good quality cam really adds to the enjoyment of the experience.
The Aomway 700tvl is probably the best camera overall: a very sharp picture, good color, not too expensive and not too heavy. I highly recommend this cam if weight is not your main consideration. If it is, the Tarot, RMRC, and Diatone are small and light enough to go on even a super micro plane or quad without screwing up the CG or aerodynamics.
SUPER IMPORTANT! If you are planning on using the Eachine, the included cable swapped the video and power wires, so yellow is power, red is video. Go figure. At least I didn't destroy the cam by plugging it in backwards. The connector is wired correctly, though, so if you have a...Continue Reading
Posted by devinvagt | Aug 06, 2015 @ 10:22 PM | 2,900 Views
Accidentally destroyed a surface mount component while changing the 5v regulator on my remzibi OSD to a recom r785.0-1.0. It's a drop in replacement for a standard 7805 with much better efficiency-no heatsink neeeded! I think later versions of this board incorporated a similar item. I tore off part of the trace along with an unidentified surface mount component. Bad bad bad.